Have an old Klipsch 4.1 speaker system? Did it die? I bet you can fix it!

titan97

Gawd
Joined
Sep 27, 2004
Messages
542
I replaced my rubber foam surrounds for the subwoofer using some I purchased from eBay for about $10. This was a few years ago and they are still working. Thanks for the original post!

Hey everyone! I made this thread back in the day to try to help folks out. I haven't been back to this site in a while - good to see people are still using this!!!!


Wanted to update everyone. I am still using my speakers. I use them connected to a laptop docking station in my home study. Last night, while listening to some bass heavy music, one of the woofers failed. The foam surround literally crumbled.

I just got off the phone with Klipsch. Although they don't make the 4.1 system anymore - they apparently make the 2.1 system, and the woofer drivers used in the 2.1 are the same as those used in the 4.1. So I ordered two of them! They should be in my hands Thursday. I'll replace both drivers in the subwoofer.

The total cost, shipped was $49. Not bad for a 17 year old system driver replacement. The guy told me they have upgraded/changed the driver surround material so the new ones should give more use. If I get another 17 years, I'll be happy.

I'll try to post here more.... HardOCP was the shit back in the day.
 
Joined
Dec 6, 2017
Messages
4
So my 4.1s have had a variety of problems, starting with the big 680uf 200v cap. I replaced that. So far so good. I then later discover one of the IRF740 mosfets on the DC to DC converter board was sheered off where it was soldered into its joints.

It done broke.

So zipties worked for a little while to hold an electrical connection but now those don't. So I have to replace it--got a NTE 2397 mosfet, apparently it is equivalent...

But I'm stuck.

The mosfet not only solders into the PCB, it is also stuck to a thick metal L-bracket plate by some sort of white substance. I assume it is using this plate as a heatsink. What do I use to stick the new one to the plate? Glue? Thermal compound? Thermal glue? Will regular CPU heatsink grease do by someone like Coolermaster?
 

Tawnos

2[H]4U
Joined
Sep 9, 2001
Messages
3,807
So my 4.1s have had a variety of problems, starting with the big 680uf 200v cap. I replaced that. So far so good. I then later discover one of the IRF740 mosfets on the DC to DC converter board was sheered off where it was soldered into its joints.

It done broke.

So zipties worked for a little while to hold an electrical connection but now those don't. So I have to replace it--got a NTE 2397 mosfet, apparently it is equivalent...

But I'm stuck.

The mosfet not only solders into the PCB, it is also stuck to a thick metal L-bracket plate by some sort of white substance. I assume it is using this plate as a heatsink. What do I use to stick the new one to the plate? Glue? Thermal compound? Thermal glue? Will regular CPU heatsink grease do by someone like Coolermaster?
It's just thermal grease on most boards, with a screw or plate holding the MOSFET to the heatsink.
 
Joined
Jan 13, 2018
Messages
1
First of all, thank you to everyone who has participated in this thread over the years. I learned a lot of extremely helpful information that has saved me immeasurable effort in getting as far as I have troubleshooting my v2.400 and special thanks to Dale Thompson (I hope I got the name right) for the extremely helpful effort and work assembling the schematics and details for these systems.



The story is long but quickly up front here are my questions:

What is the nominal voltage expected on the AMP-OC line when there is no over current condition?

What is the voltage on that line measured in reference to? Ground on the ribbon cable between IO card and Amp cards?

What voltage would be expected on that line in the event of an overvoltage?

If overvoltage is signaled, what voltage would be expected to be seen on the 0-60VDC rail from the convert card to the amp card?




The full story for those interested and in case it helps anyone else out in the future:

I have gotten pretty far in troubleshooting the problem with my system. The original problem was that suddenly one day after 15 years, the audio was extremely muted, so much that it was hard to even tell the speakers were generating any sound. This was 5 months ago and last week I finally got around to taking a look at things. I really enjoyed this system and would like it working again.

All voltage/ohm/farad measurements given below were taken with a Fluke 289 multimeter and should be reliable.

I went through all the docs and then started testing components. The first problem I found was the big cap (680uF 200v on the DC-DC converter). It measured in the Nano farads rather than 680uF, so I replaced it.

During the course of the troubleshooting, I replaced the following components so far:

-R26 on DC-DC board though it read within tolerance, it looked like it wasn’t going to last much longer
-The same with R12 on the converter board. Replaced.
-C22 and C23 (47uF) on the DC-DC board both read 50% under spec when measured out of circuit, so those were replaced.
-R27 on the DC-DC board were originally ok, but went open circuit after not isolating the Q3 and Q6 from the heat sink on one reassembly. My board only had a single 10ohm ½ watt resister and I replaced it with same.

Despite this, the same symptom remains. I have gone so far as to observe the audio signal path on an oscilloscope.

I connected a signal generator to the 1/8” input plug for the front speakers. I set it to generate an 800 Hz sine wave at 3v peak to peak.

The image below the scope screen taking signals from the signal generator output (yellow), the DIN output from the control pod (magenta), and the ribbon cable from the IO board to amplifier boards (cyan/blue). As can be seen, the signal propagates cleanly without issue through these components.



The following image shows the scope output with the same yellow and magenta probes, but this time the cyan/blue probe is reading the signal coming out of the speaker cable. As can be seen, the signal is influencing the output but it is very very low voltage (the scale can be seen at lower right on the scope screen) and it also shows what looks to be a dive voltage issue for the FETs on the amp cards.



I measured voltage at the primary interconnects:

-DC input to DC-DC card: 162 vdc
-J1 out on DC-DC card: 60.3v
-IO/Amp card ribbon cables, +15v/-15v/+20v, all at specified voltage.
-Converter board to amp boards: 53 vdc.

The voltage to the amp cards looked strong enough to be driving them so I started to think maybe an amp card issue, but just to check, I disconnected to converter 0-60vdc cable from the amp card chain and connected a bench power supply instead. I power the rest of the system and suddenly the speakers were producing normal audio again.

So the problem certainly seems to be the 0-60vdc rail supplying the amp cards, but I am not sure why the measured 53vdc output by the converter card generated only barely audible audio.

I am working to understand the function of the converter card and BASH module. One possibility that comes to mind is the AMP-OC line becoming raised and inhibiting current generation but I don’t know how to interpret the voltage on that line. I have measured it and it reads -52vdc with respect to ground on the ribbon cable. I do not know it this is normal, indicates an over current on an amp card, or is some other problem.

So if anyone happens to have any insight or ideas, please let me know.

I will continue to troubleshoot and will post back any new findings and (hopefully) the ultimate solution.
 
Joined
Dec 6, 2017
Messages
4
So I'm still nursing my Klipsch 4.1's along, and in the past year have replaced many parts since the 680uf 200v capacitor. I've replaced a MUR1620 rectifier on the DC to DC converter--which was snapped in half(probably from me kicking the sub), the two 470uf 63v capacitors on the DC to DC converter, and today the 1000uf 63v capacitor on the buck converter.

Still, the system is not perfect.

I have a strange problem that none of these have seemed to fix.

When I plug the speakers in for the first time every day, on average I must let them sit for thirty minutes to an hour before I start using them. After about 20 - 40 minutes, I will hear a hiss that may slowly develop into a quiet buzz from one or two of the speakers. The hiss is very soft and I have to put my ear close to the speaker to hear it. Once this happens, if I press the power button on the control pod and the light changes from red to green, I can then hear sound and music from the speakers.

They'll work for a while.

Sometimes many hours, sometimes a day or two, sometimes only an hour, and then... they'll go silent. But not fully silent. If I put my ear up to the speakers I can hear a very faint sound, almost like a hissing whisper from a ghost a thousand miles away. To fix... I either must unplug and let them sit for a while, or I can hit the back of the sub with my fist or heel and sometimes that will cause the hiss and buzz to return and music will start playing.

I don't know what else might be causing this, as I don't have any other caps with visible leaking to replace.

Mayhap anyone else have any ideas?
 

titan97

Gawd
Joined
Sep 27, 2004
Messages
542
Since

Since you can faintly hear sound, it sounds like the amplifier board is not doing its job. Signal is getting through, but not being amplified to its normal volume. So I would start looking there. And since your issue appears to be time or heat sensitive, I would start by checking all connectors and re-soldering as many components as I could. It might be a good time to also pull the components and test them outside of the board.
 

Nygil

n00b
Joined
May 6, 2019
Messages
1
Brand new to this great forum....still going....

I have the Pro Media 4.1 with barking subwoofer. I have had this system for many many years and love the quality of the sound.

I have seen some prior requests for a "shopping list" of resistors to replace R12 and R26, but the pics have long since been stripped from the host. If anyone has ordered and replaced these parts, I would greatly appreciate a scan or list of what and where you ordered.

Thank you so much for all the great info in this thread...

Nygil
 

TOOL1075

Gawd
Joined
Aug 29, 2002
Messages
690
Well, I started this thread 11 years ago. That's crazy.

Last night, I was getting some work done in my home office, and I heard a "pop" - now there is noise from my speakers. Sounds like a "whooshing" - loud static.

This sucks hahaha. After replacing the resistors (and why I started this thread in the first place), the only other thing I did to the speaker system was replace the subwoofer drivers because the surround material rotted away.

Now, I guess I have to go back into troubleshooting mode.

I'm glad to see this thread is still here, and so is this web forum. So that's cool.

Hope everyone is doing well :)
 

Morphes

Supreme [H]ardness
Joined
Jul 16, 2001
Messages
4,240
Man I remember my set of these, I still had the subs and the box, with plans on just replacing the amp. I looked at it the other day and the subwoofers also rotted on mine as well.
 
Joined
Dec 6, 2017
Messages
4
Finally, I think I have figured out my problem. Last night I had enough, so I got out a pair of plastic salad tongs and started poking at internal bits while the subwoofer board was plugged into the wall.

Very dangerous

And I discovered that my problem lies with the HC 1011 board. When I apply pressure to the board in just the right way, the sound starts working again! If I release pressure, the sound stops.

So...

I can't order these parts anymore. Apparently they are not sold. So I have an idea...

What if I were to use a heat gun on the part where it is soldered into the PCB to heat up the board and hopefully let the solder resettle?

The HC 1011 is plastic of some sort, so I'm not sure if that would be really bad or not, but it looks darned near impossible a job to remove, and the heatsink plate behind it that goes over it is darned near impossible to remove, too.
 

titan97

Gawd
Joined
Sep 27, 2004
Messages
542
What if I were to use a heat gun on the part where it is soldered into the PCB to heat up the board and hopefully let the solder resettle?

Give it a try. From what I remember about these boards, the soldering job from the factory was not the greatest. I seem to recall seeing several cold solder joints. Give the heat gun a try.
 
Joined
Dec 6, 2017
Messages
4
Give it a try. From what I remember about these boards, the soldering job from the factory was not the greatest. I seem to recall seeing several cold solder joints. Give the heat gun a try.

Do you have any idea if the part is plastic or ceramic or silicon?
 
Joined
Aug 29, 2013
Messages
3
First of all, thank you to everyone who has participated in this thread over the years. I learned a lot of extremely helpful information that has saved me immeasurable effort in getting as far as I have troubleshooting my v2.400 and special thanks to Dale Thompson (I hope I got the name right) for the extremely helpful effort and work assembling the schematics and details for these systems.



The story is long but quickly up front here are my questions:

What is the nominal voltage expected on the AMP-OC line when there is no over current condition?

What is the voltage on that line measured in reference to? Ground on the ribbon cable between IO card and Amp cards?

What voltage would be expected on that line in the event of an overvoltage?

If overvoltage is signaled, what voltage would be expected to be seen on the 0-60VDC rail from the convert card to the amp card?


I will continue to troubleshoot and will post back any new findings and (hopefully) the ultimate solution.


Hey Patrick,

My issues sound very similar to what you were experiencing. Did you ever figure yours out?

I have done much of the same troubleshooting as you(minus the oscilloscope) so far but still having the low volume, distorted, echo'y sound from the satellites. I have replaced the common trouble parts, R12 on the digital converter and R26 on the DC-DC board as both were crispy but still reading ok, I initially thought R12 was definitely the problem as when I touched it the solder pad basically disintegrated(on the diode side, closest to the corner of the board). Unfortunately there must be other issues as replacing it and soldering the one leg to the diode next to it didn't solve the issue. I seem to have no output on CD +/- from the digital converter. Is this supposed to be just DC voltage or is it a digital signal that I would need to check with a scope? Leads me to believe something is amiss with the digital converter board. I am getting the 60VDC coming in to the digital converter so I think everything before the digital converter seems to be working as intended. I checked the other DC voltages(30, 15 etc) and those seemed to be in check as well. I am going to try replacing the 1000uf cap on the converter board as it looks like it may have leaked out the bottom, I don't have a capacitance meter to check but have a replacement so may as well try replacing it, I guess. Anyways, hopefully you still check this site and can chime in. Thanks!
 

Arcygenical

Fully [H]
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Jun 10, 2005
Messages
25,059
I know we all love these computer speakers, as they were an icon of years passed, but 5 channel class D amps are super cheap now... Even A/B if you don't mind the power draw. The speakers are clearly still great, why just not swap out the board entirely, load up a new pot for volume, and re-run a few cables? Might cost <50$ from ebay/aliexpress parts - and use lots of these without issue all over my house.
 

Burticus

Supreme [H]ardness
Joined
Nov 7, 2005
Messages
4,414
Wow this thread is old enough to have a full beard I think.

My Klipsch Promedia's are still kicking, tripped across this thread. I bought the 4.1 set back in 2000. Had a bad power surge at my house around 2008-2009 that blew up a ton of stuff in my house, including the sub amp and fried the 2 front speakers. I swapped the rears to the front, and had the amp repaired/replaced by the infamous Elliot dude from the other Promedia thread. That was not a hassle free experience, but he eventually produced a working sub amp. Now, in 2020, the amp kinda comes and goes sometimes... I kick the sub a little and it comes back on. Also the volume pot is awful, so I leave it turned up to like 50% all the time (only way to get stable left/right, and I did try deoxit spray) and then use computer volume controls. This mostly works except sometimes after reboot the windows volume resets to 100% and it will be super loud until I bring it back down, I have given my cats heart attacks a couple times :) .

If/when it fails outright I think I'll either try to replace the sub amp with something from parts express (or maybe just get a new powered sub)... I have an older Yamaha amp collecting dust I could use for power for the mains, but not really desk room for it.

edit - wow Klipsch still sells these things, 2.1 $149 directly from their site. Bestbuy used to carry it, but no longer. All the other etailers (amz etc) are over $200.
 

XRaVeNX

n00b
Joined
Jan 9, 2021
Messages
6
Can't believe this thread is still going! I have the v.2-400. So, recently (within the last few months), the speakers started emitting distortion whenever sound is played on them. I read through this thread discovered I have a blown R26 (was reading 48K Ohm), and possibly R12 (was reading 620 Ohm). So I ordered myself replacements (with higher wattages):

https://www.digikey.ca/en/products/detail/te-connectivity-passive-product/RR03J47KTB/8603785
and
https://www.digikey.ca/en/products/detail/te-connectivity-passive-product/ROX3SJ680R/8603714

Replaced them. I'm not the best with the soldering iron and almost screwed up with R12. In the process of trying to remove the old resistor, I pulled off the pad on the board. I managed to still solder it on after many attempts and frustrations.

After reassembling the subwoofer, I reconnected everything and at first, everything seemed fine. Fixed! There was no more distortion. However, there is still very low volume whining/buzzing (the pitch changes a bit when I adjust the volume knob). And over time, the pitch also changes on its own (without any intervention). After about 4-5 minutes, it suddenly made a loud boom and everything turned off (control pod LED is off).

I opened it up again and it appears the fuse has blown (checked for continuity of the fuse and it is dead). There was also a black scorch mark on the aluminum support brackets on the DC-DC converter beside big black 600u 200V capacitor. When I initially opened the sub, a lot of the components were very hot still.

So my question is, before I replace this fuse, what was causing the whine/buzzing? I have a feeling it is related to why the fuse blew.
 

titan97

Gawd
Joined
Sep 27, 2004
Messages
542
Can't believe this thread is still going! I have the v.2-400. So, recently (within the last few months), the speakers started emitting distortion whenever sound is played on them. I read through this thread discovered I have a blown R26 (was reading 48K Ohm), and possibly R12 (was reading 620 Ohm). So I ordered myself replacements (with higher wattages):

https://www.digikey.ca/en/products/detail/te-connectivity-passive-product/RR03J47KTB/8603785
and
https://www.digikey.ca/en/products/detail/te-connectivity-passive-product/ROX3SJ680R/8603714

Replaced them. I'm not the best with the soldering iron and almost screwed up with R12. In the process of trying to remove the old resistor, I pulled off the pad on the board. I managed to still solder it on after many attempts and frustrations.

After reassembling the subwoofer, I reconnected everything and at first, everything seemed fine. Fixed! There was no more distortion. However, there is still very low volume whining/buzzing (the pitch changes a bit when I adjust the volume knob). And over time, the pitch also changes on its own (without any intervention). After about 4-5 minutes, it suddenly made a loud boom and everything turned off (control pod LED is off).

I opened it up again and it appears the fuse has blown (checked for continuity of the fuse and it is dead). There was also a black scorch mark on the aluminum support brackets on the DC-DC converter beside big black 600u 200V capacitor. When I initially opened the sub, a lot of the components were very hot still.

So my question is, before I replace this fuse, what was causing the whine/buzzing? I have a feeling it is related to why the fuse blew.
Whine or buzz is usually related to unfiltered AC coming through the DC signal. I would unplug the various boards before I started troubleshooting this. I would check the rectifier (mine looked like a tall black square with one corner cut off and a hole in the middle. It has 5 pins.) Mine died and needed to be replaced. The rectifier converts the AC power to DC power, and if it isn't working, it can pass AC power through to the downstream circuits. You should also check all of the other components on the AC-to-DC converter board. Bad capacitors can fail to do whatever filtering they should be doing, and bad resistors can cause an filtering circuit to stop altogether.

You also need to check all of the other devices for a short to ground. The fact that you see scorch marks indicates that a ton of power was going through the converter. Since the DC-to-DC converter ramps up the voltage (if I recall correctly), any AC going through this system may also be ramped up. I'd have to relearn the schematics and system to confirm this, but it's something that I would check out if I were you.
 

XRaVeNX

n00b
Joined
Jan 9, 2021
Messages
6
Whine or buzz is usually related to unfiltered AC coming through the DC signal. I would unplug the various boards before I started troubleshooting this. I would check the rectifier (mine looked like a tall black square with one corner cut off and a hole in the middle. It has 5 pins.) Mine died and needed to be replaced. The rectifier converts the AC power to DC power, and if it isn't working, it can pass AC power through to the downstream circuits. You should also check all of the other components on the AC-to-DC converter board. Bad capacitors can fail to do whatever filtering they should be doing, and bad resistors can cause an filtering circuit to stop altogether.

You also need to check all of the other devices for a short to ground. The fact that you see scorch marks indicates that a ton of power was going through the converter. Since the DC-to-DC converter ramps up the voltage (if I recall correctly), any AC going through this system may also be ramped up. I'd have to relearn the schematics and system to confirm this, but it's something that I would check out if I were you.
So I've removed the entire I/O board and disconnected all connections to other boards.

Using this diagram as reference: http://www.thompdale.com/bash_amplifier/4-1/4-1_i-o_board_986x709.gif

I have located the rectifier (D4, GBU606), bottom left of the diagram. Using the diode function on my multimeter, I got:
Forward bias voltage of 0.5V between pins 4 and 2, pins 2 and 1, pins 4 and 3, pins 3 and 1.
Forward bias voltage of 0.95V between pins 4 and 1.
Reverse voltage on 0V on all combinations of pins listed above.

So what I think the rectifier is working fine???

Note: R25 and C16 doesn't actually exist on the board??? Is this normal?

How do I go about checking capacitors? Do I have to desolder them off the board?

I am going to pick up some more fuses tomorrow and see what happens when I only power the I/O board up (disconnected from all other boards). In the mean time, I'll appreciate any suggestions and also I'm gonna go test any resistors I see.
 
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titan97

Gawd
Joined
Sep 27, 2004
Messages
542
So I've removed the entire I/O board and disconnected all connections to other boards.

Using this diagram as reference: http://www.thompdale.com/bash_amplifier/4-1/4-1_i-o_board_986x709.gif

I have located the rectifier (D4, GBU606), bottom left of the diagram. Using the diode function on my multimeter, I got:
Forward bias voltage of 0.5V between pins 4 and 2, pins 2 and 1, pins 4 and 3, pins 3 and 1.
Forward bias voltage of 0.95V between pins 4 and 1.
Reverse voltage on 0V on all combinations of pins listed above.

So what I think the rectifier is working fine???

Note: R25 and C16 doesn't actually exist on the board??? Is this normal?

How do I go about checking capacitors? Do I have to desolder them off the board?

I am going to pick up some more fuses tomorrow and see what happens when I only power the I/O board up (disconnected from all other boards). In the mean time, I'll appreciate any suggestions and also I'm gonna go test any resistors I see.
The R25 and C16 are marked on the schematic as DNI (do not insert or do not include), so they should be absent.

To check capacitors, you have to desolder at least one lead and make sure that it does not contact the mounting hole. I normally just desolder both legs and remove the whole cap. Go ahead and check all of the caps and resistors that you can.

With the I/O board completely disconnected from the other boards (and the fuse replaced), power it on with AC and see what the DC+ and DC- readings are. If that looks good (I think the voltage is like 80-100VDC, but I don't recall exactly), then we need to check the next downstream circuit. First, we need to see if that board has a short to ground, so use your multimeter and follow the schematic, checking each component for a short. If that looks good, then connect the next board and follow the voltage.
 

XRaVeNX

n00b
Joined
Jan 9, 2021
Messages
6
The R25 and C16 are marked on the schematic as DNI (do not insert or do not include), so they should be absent.

To check capacitors, you have to desolder at least one lead and make sure that it does not contact the mounting hole. I normally just desolder both legs and remove the whole cap. Go ahead and check all of the caps and resistors that you can.

With the I/O board completely disconnected from the other boards (and the fuse replaced), power it on with AC and see what the DC+ and DC- readings are. If that looks good (I think the voltage is like 80-100VDC, but I don't recall exactly), then we need to check the next downstream circuit. First, we need to see if that board has a short to ground, so use your multimeter and follow the schematic, checking each component for a short. If that looks good, then connect the next board and follow the voltage.
So, isolated the I/O board and powered it up. No major issues. Two things of note:
  • DC+ (F03) and DC- (F04) reads 111V. Although the block diagram here indicates it should be 156V??
  • The 5-pin Power Supply ribbon cable that goes to the DC-DC Inverter Board is reading:
    • Between J1:1 to J1:3 = 0.24V
    • Between J1:3 to J1:5 = 90mV
    • Between J1:1 to J1:5 = 0.33V

Anyway, I then proceeded to isolate the DC-DC Inverter Board. I disconnected the F03 and F04 output to the Digital Converter Board. So, the I/O Board is connected to the DC-DC Inverter Board via the F03/w2-F04/w1 to F01/w3-F02/w4.

I connected power and immediately, sparks from I believe to be the transformer coil area (T1 per this diagram). The big yellow thing that says "Danger High Voltage". See attached picture. You can see that scorch mark there. There's also this brown gooey substance over all four corners of that thing where the metal clips are. Not sure if that's normal.

Mind you, the only thing I've replaced on this board is the infamous R26 with a 47K Ohm 5W Resistor.

So I'm at a loss at what is broken. Is the I/O board not supplying the proper voltages to the DC-DC Converter, thus causing the sparks? Or is there also something wrong with the DC-DC Converter?

How do I go about checking the windings on the transformer? Perhaps it's shorting on itself? Is it safe to touch it when the entire system is powered off (the "Danger High Voltage", is giving me pause) ?
 

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titan97

Gawd
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542
I believe that the 156V is incorrect. If you rectify 120VAC, without any sort of step-up transformer, then 110VDC sounds about normal. That 110VDC then goes through two wires to the DC/DC converter board, where it is transformed into 30VDC and 60VDC. The 30V goes back to the I/O board. The 60V goes to the digital converter board. If you are getting sparks from the transformer then it probably has a short. Can you remove it and check the resistance across various legs.
 

XRaVeNX

n00b
Joined
Jan 9, 2021
Messages
6
I believe that the 156V is incorrect. If you rectify 120VAC, without any sort of step-up transformer, then 110VDC sounds about normal. That 110VDC then goes through two wires to the DC/DC converter board, where it is transformed into 30VDC and 60VDC. The 30V goes back to the I/O board. The 60V goes to the digital converter board. If you are getting sparks from the transformer then it probably has a short. Can you remove it and check the resistance across various legs.
I can. But is it safe to do so? I don't wanna get hurt trying to desolder it off the board.
 

XRaVeNX

n00b
Joined
Jan 9, 2021
Messages
6
Okay. So I've taken the entire DC-DC Inverter Board out and removed the transformer off the board.

On the board itself, I've tested all the resistors. The only two that are out of spec:
  • R15 which is supposed to be 475 Ohms, but I'm reading 32 Ohms
  • R7 which is supposed to be 250K Ohms, but the reading kept changing. It ranged anywhere from 3 Mega Ohms, to 15 K Ohms. And it would slowly decrease or increase. I have a feeling a charged capacitor somewhere is messing with the readings.
The transformer itself doesn't appears to be shorting to ground. I did a continuity test of each of the legs of the transformer. If you look at the attached photos, each pair of legs forms a loop (i.e. positive continuity). So example, if we numbered each leg in the photo starting from the top left 1, 2, 3, etc. 1 and 2 are connected. 3 and 4 are connected, 5 and 6 are connected, etc. So I'm guessing this is normal?

I've also taken some photos of some of my capacitors that appear to be leaking or that just glue? Is that what leaking looks like? If so I can try and replace them.


Also, thanks for your help so far. Any way we can chat on Discord or something?
 

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titan97

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Sep 27, 2004
Messages
542
What are the ohms for each coil of the transformer? Test the primary and secondary windings. This part of the schematic begins to look Greek to me, since the various transistors and such are not something that I'm familiar with, so I'd rely on the internet on how to test the transformer and the circuit. I do note that most of the resistors in the schematic are listed at 475 Ohms. What does the color code bands of R15 indicate, 32 Ohms (probably the more common 33 Ohms) or 475 Ohms? Are the color bands on R15 the same as the other listed 475 Ohm resistors? The leads on R7 are common with the two capacitors in the schematic (C7 and one unlabeled @ 680uF), so I would expect the readings to change as you measure it. You will need to remove at least 1 leg from the circuit in order to test it accurately. When I look at the other pieces of the first circuit for the primary on the transformer, I'd pull off and test these items: R2, R5, R7, R14, R15, R25, R28, Z1, Z2, D4, D7, C9, C20, the big black cap.

That large black cap doesn't look healthy. It just might be the image, but it appears to be bulging on the top. Short the leads with a plastic-handled screwdriver and then remove the cap, then test the capacitance. If you look at some of the photos on the thompdale site, his caps have the ring of dark stuff along the board, too.

Let me check my schedule this weekend, and I may be able to chat for a bit on Sunday.
 

B00nie

[H]F Junkie
Joined
Nov 1, 2012
Messages
8,642
Finally, I think I have figured out my problem. Last night I had enough, so I got out a pair of plastic salad tongs and started poking at internal bits while the subwoofer board was plugged into the wall.

Very dangerous
I remember my late father using his finger when analyzing tv or amplifier boards. He would put a little saliva to his fingertip and then probe different connections on the board and observe what happens. By listening and looking, he could pinpoint usually the problem within a few seconds and then fix it. There were all kinds of legsnds of his repair ability, one time he was called to a womans home to see the tv and he used the ladys hairpin to fix the tv :)

Another time there was a radio that had been dropped to the sea. Two other repairmen worked for days without managing to fix it, my father got it working in 10 minutes. :) I certainly wouldn't recommend doing _any_ repairwork when the device is powered on though. One wrong move of the finger can lead to a fatal accident or serious burn. Especially with things like an analog tv where there are very high voltages present. Gosh, now I remembered the coil whine typical to those old those old analog tvs... hurt my ears.
 

XRaVeNX

n00b
Joined
Jan 9, 2021
Messages
6
What are the ohms for each coil of the transformer?
I'm not sure what you mean by that. Pin 1 to Pin 2 on the transformer is connected to each other, so 0 Ohms resistance. Same goes for Pin 3 to Pin 4, Pin 5 to Pin 6, etc.

I'm not entirely sure how to test the transformer or its windings. I can't find any specifications for this transformer anywhere, so I have no idea?


Regarding R15, the colours are Yellow, Purple, Green, Black, Gold = 475 Ohms 5%. It's the same as R2. But as you can see in the picture attached, there appears to be a blemish on R15. It doesn't surprise me because it is near where the sparks emanated from. This may have also damaged Q4 in the picture as well (see below). May be damaged hence why it is reading 32 Ohms. I can easily get a 470 Ohm replacement resistor, do you think that's good enough? Or do I have to get an exact 475 Ohm resistor?

20210115_202745-r.jpg



I unsoldered one leg of R7 and got a reading of 210K Ohm. Diagram indicates it should be 205K Ohm... so within tolerance?

I removed C8 (the big 680u 200V black capacitor) and tested it. I don't have a capacitance meter so I couldn't verify its capacitance. But I tested with a multimeter for resistance and it was slowly increasing in resistance as expected. I also charged the capacitor up with 9V battery and did a voltage test and read 10V (with a very slow decline). So I think C8 is fine. It isn't bulging and I can tell the black stuff around the cap is not leaking.
20210115_214206-r.jpg


Finally, I removed the aluminum shrould/heatsink and discovered I may have a bad IC. Q4 appears to have suffered some damage:
20210115_213932-r.jpg


In comparison to Q5 which seems to be fine:
20210115_214006-r.jpg


How do I go about testing Q4?
 
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