I have a 70s model Biamp TC-225 professional power amp that needs to be repaired. This thing has two channels with 225 watts at 8 ohms on each channel and 600 watts bridged. One of the channels has quit working (no sound). I used this amp with my old Carvin PB-15 to drive a David Eden 410 cab. I recently changed my pre to a David Eden WTDI. Does anyone have any suggestions on where to start troubleshooting this amp?
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BiAmp TC-225 Repair
- Thread starter MikeBwiz
- Start date
- Feb 12, 2006
- 61,086
- 5
- 221,200
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Start with standard techniques, DMM, scope and signal generator.
Iirc, they are a bit tough to work on, but not impossible.
Iirc, they are a bit tough to work on, but not impossible.
- Feb 12, 2006
- 61,086
- 5
- 221,200
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
The part of the circuit responsible for the failure. (not being intentionally sarcastic here)
Do you understand how the circuit is supposed to work? What is your background? Do you have a variac, scope, signal generator and DMM?
The answer to your question is that even though I am somewhat familiar with the amp, I haven't seen one in a long time, I have no idea what may be wrong, or where it may be located in the circuit without going through proper troubleshooting. There's a lot going on in that amp, so you are going to know how to troubleshoot discrete global feedback circuits with some unusual current source biasing.
Have have a basic understanding of how electronics circuitry works. I did take several classes using an oscilloscope but that was well over two decades past. I am generally proficient in understanding most tech subjects as I am a research chemist by trade. I do have a DMM and a very cheap hand held oscilloscope from Amazon. I have already tried to have it serviced professionally but I have been able to find someone that is willing to work on a solid state amplifier. That being said I am not looming for an exact solution. Just a general idea of were to start my research on troubleshooting this guy. Thanks for the input.
Sorry. I have NOT been able to find anyone that is willing to work on it. I'm not a professional by any means but I am not your stereotypical stoner guitarist that doesn't know how his equipment works. I am the most dangerous type of person, one with a little bit of know how and an appetite to learn more. So I fully understand that I will probably break something and end up in the hospital...
- Feb 12, 2006
- 61,086
- 5
- 221,200
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Spend some time learning how the circuit works, then you will have a better idea what's involved with troubleshooting. It's a fairly involved amp with some tricky bits to it. Any pro audio guy worth his salt shouldn't have an issue with it though.
I definitely think this is good advice. I had planned on working on an old GK amp that uses Class G or H. I took vocational electronics in high school and also was a military electronic tech in the late 80s. But there is some circuitry in this topology that I have not studied. Overall Class G/H sort of reminds me of a clenched muscle, because there appears to be so much feedback throughout the circuit.
I spend quite a bit of time researching the topology and felt I had at a basic grasp over how it worked and how to troubleshoot it. But ultimately I put it aside as a lost cause because the output and driver devices are obsolete and very difficult to source. I did actually find sources, but minimum purchase quantity was 50 each.
Also I don't own an oscilloscope. With an oscilloscope and available parts I am sure I could eventually fix it, but the damage is pretty significant. I bought a component tester and found that almost all of the output devices were shorted and there were also several burned resistors and diodes in earlier sections of circuit. I am sure there was probably significant collateral damage surrounding the burned components. Given the way this topology works, I could see how a failure might be very catastrophic.
I wound up buying a beater amp to cannibalize. It was supposed to be fully functional, but only 1 of 2 output cards worked. The original amp I wanted to fix is older, but cosmetically very clean. I wound up doing a technical update to the good output module, so it would perform the same as the cannibalized module. Eventually I also cannibalized the preamp and I/O cards which also had been fully updated The original amp looked nice, but turned out to be quite the lemon. The only original parts left are essentially the chassis, transformer, and one updated output module.
This may be a fun project. IMHO, the fun part is the only reason to pursue it. I am very confident you could buy a used amp that would easily outperform the old Biamp for a very low price.
I have set up Guitar Center used to sort Used Live Power Amps from Lowest to Highest Price:
https://www.guitarcenter.com/Used/L...profileCountryCode=US&profileCurrencyCode=USD
Good luck!
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Thanks Wasnex. I agree the amp is quite outdated and the motivator to fix this thing is sentimental. It belonged to my late father. I would also like to learn enough to troubleshoot amps in the future as I am a self proclaimed technologist. I spend a boat load of time in my career learning how to troubleshoot and maintain lab equipment (GCMS, HPLC, FTNIR, etc.). I fully intend to replace the amp with an upgrade regardless of the outcome of this project. I am a tinkerer at heart.
