Hifonics VI Colossus amp half in protect
Started working on an old Zed Hifonics VI Colossus, which is essentially 2x Mono block amps I believe inside. Separate everything.
One of the amps powers up fine. Not sure if it will play though as I'm servicing the other amp which has the RCAs on it.
The bad amp, with RCAs, powers up for about 5 seconds or so and then falls into protect. My DVM is sensing +2~3vDC on speaker terminal which rises up to about +3vDC before the amp kicks into protect. Positive and negative rail voltage seems to be alright during that time. I found numerous bad solder joints which I cleaned up. Rail caps are testing good off the PCB.
There are no opamps on this board, only discrete components. Regulated voltage appears to be OK.
I've not seen very many VI amps.
Does anyone know what components I can remove to keep the amp powered up for testing, or any other thoughts as to why there would be +DC on speaker terminals?
Photos in a moment.
Thank you
Started working on an old Zed Hifonics VI Colossus, which is essentially 2x Mono block amps I believe inside. Separate everything.
One of the amps powers up fine. Not sure if it will play though as I'm servicing the other amp which has the RCAs on it.
The bad amp, with RCAs, powers up for about 5 seconds or so and then falls into protect. My DVM is sensing +2~3vDC on speaker terminal which rises up to about +3vDC before the amp kicks into protect. Positive and negative rail voltage seems to be alright during that time. I found numerous bad solder joints which I cleaned up. Rail caps are testing good off the PCB.
There are no opamps on this board, only discrete components. Regulated voltage appears to be OK.
I've not seen very many VI amps.
Does anyone know what components I can remove to keep the amp powered up for testing, or any other thoughts as to why there would be +DC on speaker terminals?
Photos in a moment.
Thank you
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That’s next. There are no noticeable shorts without removing the outputs and there’s low ohm resistors in circuit making testing the outputs tricky. I combed through all smaller transistors in the audio circuit and found none to be an issue though after de and re soldering them all; the amp will now stay powered with D9 in circuit. 1.8vDC on speaker terminals. Same bad wavelength at high input. So something changed.
Green wire should be fine. Secondary ground is just about everywhere in the amp from the toroid, rcas, green, etc. Large traces straight thru the middle of the pcb.
With no input, Putting a load on, does reduce the DC on the speaker terminals slightly, but the test speaker gets sucked in - no good. It also starts to draw much more current. I don't think there is an issue with the output side of this amp at all though.
I believe the problem is somewhere at the very beginning stages of the Pre-Amp at this point. With no input connected, there is -5.8vDC on this amp's RCA center connector. (This amp is using the RCA input that is CLOSEST to the actual PCB). When I attach my frequency generator that voltage goes down close to zero though, pulled down by the generator.
Q1 is a 2sC2389, which is measuring OK off the PCB.
I removed several components from this amp to test them. So far everything seems to be testing out OK. Pulling the driver board I believe totally disconnected the output side from the pre-amp, yet I'm still having pre-amp and sensing massively distorted high input signal on many components.
Focusing on Q1 and Q3 in the above photos, pads are measuring oddly especially Q1.
Q1 (REMOVED)
1. -34.4
2. -0.35
3. 0
Q3 (REMOVED)
1. -0.35
2. 0
3. 0
Q1 (INSTALLED)
1. -6.5
2. -6.48
3. -5.84
Q3 (INSTALLED)
1. -5.84
2. -5.28
3. -5.23
I believe the problem is somewhere at the very beginning stages of the Pre-Amp at this point. With no input connected, there is -5.8vDC on this amp's RCA center connector. (This amp is using the RCA input that is CLOSEST to the actual PCB). When I attach my frequency generator that voltage goes down close to zero though, pulled down by the generator.
Q1 is a 2sC2389, which is measuring OK off the PCB.
I removed several components from this amp to test them. So far everything seems to be testing out OK. Pulling the driver board I believe totally disconnected the output side from the pre-amp, yet I'm still having pre-amp and sensing massively distorted high input signal on many components.
Focusing on Q1 and Q3 in the above photos, pads are measuring oddly especially Q1.
Q1 (REMOVED)
1. -34.4
2. -0.35
3. 0
Q3 (REMOVED)
1. -0.35
2. 0
3. 0
Q1 (INSTALLED)
1. -6.5
2. -6.48
3. -5.84
Q3 (INSTALLED)
1. -5.84
2. -5.28
3. -5.23
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So the manual actually states that this amp is bridgeable by connection RED and BLACK between the two amps; to the speakers. That seems a little strange to me to be honest but I'm not so sure thats actually the case here.
Was this amp really bridgeable?
Asking really because I don't see any commonality/connection between these two amps except through amplifier's general power connections. I would have thought that a bridgeable amp would at least have some sort of common secondary ground. These amps are wired independently except for just the RCA signals.
The second amp in this case is also having a very similar problem, and is completely missing negative signal as driven, at the speaker terminal. So I cant really use this amp to compare to the first amp exactly.
Also I've noticed that the first amp will fall into protect with all components installed with RCAs disconnected. If I connect RCAs, the amp will stay powered up.
Was this amp really bridgeable?
Asking really because I don't see any commonality/connection between these two amps except through amplifier's general power connections. I would have thought that a bridgeable amp would at least have some sort of common secondary ground. These amps are wired independently except for just the RCA signals.
The second amp in this case is also having a very similar problem, and is completely missing negative signal as driven, at the speaker terminal. So I cant really use this amp to compare to the first amp exactly.
Also I've noticed that the first amp will fall into protect with all components installed with RCAs disconnected. If I connect RCAs, the amp will stay powered up.
I re-installed all components and put everything back into the amp.
I also might be on to something but I'm not really sure. That is the gain control isn't doing hardly anything at all in amp1, and absolutely nothing for amp2. I have a hunch that whatever the gain control is trying to control has failed, but I cant get much read on what exactly that is.
I also might be on to something but I'm not really sure. That is the gain control isn't doing hardly anything at all in amp1, and absolutely nothing for amp2. I have a hunch that whatever the gain control is trying to control has failed, but I cant get much read on what exactly that is.
I should have known better, but then again this amp doesn't have opamps nor regulators so I overlooked one HUGE thing, that is; regulated voltage. It was mentioned to me by someone on FB that I could check that and so I did.
This amp is using large 2.7k 2w resistors to drop +-76v rail down to about +-34vdc for regulated voltage. Those resistors are R16 and R17 located somewhat near the RCAs and both amps have them.
On both amps, R16 and R17 look a little cracked and overworked.
Amp1 had R16 blown open
Amp2 had R17 blown open.
I replaced R16 in Amp1, and the amp has clean output, drive, signal, gain control works etc; out to clipping under no load. I have not tested under load yet but I'm sure that was a major issue/factor here.
Unless there are suggestions or otherwise modifications needed to make these amps stable, I'm going to replace R16/R17 in BOTH amps with 2.7k 5w units and go from there. I bet Zed Tech does some nice reliability upgrades; but I have no idea.
This amp is using large 2.7k 2w resistors to drop +-76v rail down to about +-34vdc for regulated voltage. Those resistors are R16 and R17 located somewhat near the RCAs and both amps have them.
On both amps, R16 and R17 look a little cracked and overworked.
Amp1 had R16 blown open
Amp2 had R17 blown open.
I replaced R16 in Amp1, and the amp has clean output, drive, signal, gain control works etc; out to clipping under no load. I have not tested under load yet but I'm sure that was a major issue/factor here.
Unless there are suggestions or otherwise modifications needed to make these amps stable, I'm going to replace R16/R17 in BOTH amps with 2.7k 5w units and go from there. I bet Zed Tech does some nice reliability upgrades; but I have no idea.
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