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

Discussion in 'Computer Audio' started by TOOL1075, Aug 8, 2008.

  1. titan97

    titan97 Limp Gawd

    Sep 27, 2004
    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!

  2. TOOL1075

    TOOL1075 Gawd

    Aug 29, 2002
  3. Mr_Blastman

    Mr_Blastman n00bie

    Dec 6, 2017
    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?
  4. Tawnos

    Tawnos 2[H]4U

    Sep 9, 2001
    It's just thermal grease on most boards, with a screw or plate holding the MOSFET to the heatsink.
  5. Patrick Oneill

    Patrick Oneill n00bie

    Jan 13, 2018
    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.