Hello everyone,
Nothing is visually damaged on this board, I have measured the DC coming from the PSU and compared it to the right channel and it’s correct, even the LEDs light up, I have also noticed that they stay lit much longer than the ones on the right side after turning the Amp off.
I’m not a Pro, I got 2 of these amps because of what they represent and I was hoping I could fix them but with the very little information I could find about them it looks like I chose the wrong Amp to learn 🙂
Any suggestions from those that have seen something similar?
Any common issues that I should be tackling first?
Thanks in Advance!!
Nothing is visually damaged on this board, I have measured the DC coming from the PSU and compared it to the right channel and it’s correct, even the LEDs light up, I have also noticed that they stay lit much longer than the ones on the right side after turning the Amp off.
I’m not a Pro, I got 2 of these amps because of what they represent and I was hoping I could fix them but with the very little information I could find about them it looks like I chose the wrong Amp to learn 🙂
Any suggestions from those that have seen something similar?
Any common issues that I should be tackling first?
Thanks in Advance!!
I tested all components from this board today and I found that R32 10k ohm was open so I went ahead and replaced it, assembled the whole thing back which is a pain in the rear and connected everything, I turned the Amp On and left it on for a minute and the LEDs turned off as they should, exactly at the same speed as the ones on the right channel.
Ok all happiness so far...
Then I turned the Amp back on and left it warm up for about 5 minutes, then I was going to connect a speaker but Fortunately I remembered to check DC offset first, I’m glad I did, it was the whole 60-65 Volts.
So I got disappointed and turned the App off and again the LEDs stayed lit.
This time R32 is not open so who knows if it blew something else this time... Will test everything again when I get a chance and see.
Again, any ideas, suggestions, what should I have done after replacing R32?
Thanks!!!
Ok all happiness so far...
Then I turned the Amp back on and left it warm up for about 5 minutes, then I was going to connect a speaker but Fortunately I remembered to check DC offset first, I’m glad I did, it was the whole 60-65 Volts.
So I got disappointed and turned the App off and again the LEDs stayed lit.
This time R32 is not open so who knows if it blew something else this time... Will test everything again when I get a chance and see.
Again, any ideas, suggestions, what should I have done after replacing R32?
Thanks!!!
Go sign up at Hifiengine.com where you can download the service manual for free.
You're right about probably being the wrong amp to learn on. It has what many consider to be lethal Voltages (+/- 70 V ). More importantly it's mostly MOSFETs which is not a bad thing but they tend to be less forgiving of careless handling - namely static.
If it were mine I'd verify all the power supplies and fuses are intact. NOT blown fuses with a 60 Volt offset indicate to me the output devices are likely all good and they are being driven wrong because of a fault near the input area. This could be a failed transistor (bipolar or MOSFET) or an open resistor. Non electrolytic caps do fail but in my experience it's VERY VERY rare.
Over the years I've run into failed PC boards usually from acid leaking from 'lytic capacitors that eats away the copper traces. IOW, do not discount the actual board.
Once you get the service manual you can compare the Voltages of a good channel to a bad one. That should get you to the bad component.
BE VERY CAREFUL ABOUT 'FAT PROBING' COMPONENTS. With 140 Volts at 10 amps, BAD things can happen which can get expensive and scare the bejesus out of you.
Good luck
G²
Thanks!
I do have the manual from day 1 and have been checking continuity from point to point as you suggest and everything is OK.
The only voltage that I have tested is the one coming out of the Power Source and it does match the right channel, are you suggesting that I need to check voltage in every component of the board while its powered?
I do have the manual from day 1 and have been checking continuity from point to point as you suggest and everything is OK.
The only voltage that I have tested is the one coming out of the Power Source and it does match the right channel, are you suggesting that I need to check voltage in every component of the board while its powered?
I'd like to discard power supply problems, is it fair to assume that if the VDC coming out of it is the same as in the right channel then it is OK and I should focus on the Amp board instead?
What is a "power source" ? Do you mean the amplifier output connector? With no signal connected it should be 0 or very close to it (0-50 mV +/-) Values other than close to 0 means it needs repair on that channel. If both channels are far from 0 it means they a BOTH need repair. If they're "the same" that means very little except both channels need repair.
First are ALL power supplies present AND the correct value? All 7 fuses are good? The manual I have shows +/- 70 and +/- 85 going to the amplifier but the power supply section shows +/- 81 for the main power and +/- 91 regulated. The +/- 70/81 Volt supplies are not regulated and will vary with line Voltage. Adcom states this is nominally 115.
Each channel shows 2 "fuse fault" LEDs. All 4 should be lit. I believe the "error" and "thermal" LEDs for each channel should be off.
If ANY of this is the LEAST BIT unclear I think you should stop before you hurt yourself or the amplifier.
G²
Sorry I meant Power Supply.
No DC offset in the right channel.
Yes All 7 fuses are good, have tested continuity and resistance, all OK.
I have measured the voltages and they are higher than in the manual but both channels match the un regulated is around +/- 85 Volts and the Regulated is around +/- 95.
As you can see the values in the manual don’t match, the values coming out of the Power Supplies are different to what’s theoretically coming into the Amp Board, and believe me, there are many other mistakes in that manual, specially with capacitor values and types.
Yes, all 4 fault LEDs are lit and the error and thermal front panel LEDs are off.
You are correct if I didn’t understand these basic concepts I shouldn’t even have opened the Amplifiers.
Now, back to my question, with all this being OK should I focus on the Amp Board then??
I can source most of the parts from Mouser except for the IRF244 and IRF9240 but I’m really hoping those are OK.
What do you think?
Thanks!!!
No DC offset in the right channel.
Yes All 7 fuses are good, have tested continuity and resistance, all OK.
I have measured the voltages and they are higher than in the manual but both channels match the un regulated is around +/- 85 Volts and the Regulated is around +/- 95.
As you can see the values in the manual don’t match, the values coming out of the Power Supplies are different to what’s theoretically coming into the Amp Board, and believe me, there are many other mistakes in that manual, specially with capacitor values and types.
Yes, all 4 fault LEDs are lit and the error and thermal front panel LEDs are off.
You are correct if I didn’t understand these basic concepts I shouldn’t even have opened the Amplifiers.
Now, back to my question, with all this being OK should I focus on the Amp Board then??
I can source most of the parts from Mouser except for the IRF244 and IRF9240 but I’m really hoping those are OK.
What do you think?
Thanks!!!
I would pay LOTS of attention to the area of Q6. Q4 and Q6 are current sources for the differential and Voltage amp respectively. Notice the thermal breaker (TB101) disables power to Z4 which shuts off the entire input section and turns on Q14 and the "thermal" LED. The output and bias then goes to 0 (no current, high impedance) without any drive. Since your amp is going positive it appears Q4 is doing its job but Q6 is not. Open resistor R6 or R12 (failed resistor or bad solder) would do the same.
G²
G²
That's great help, Thanks!!!
I tested Q4 and Q6 and they both come up correctly in basic DMM diode test as well as in one of those Chinese component testers, in the past usually when a transistor is bad that Chinese tester would ID it as 2 resistors but I know transistors can be bad in different ways not only shorted, would you recommend a better testing method, perhaps a good affordable tool for this kind of tests?
I tested Q4 and Q6 and they both come up correctly in basic DMM diode test as well as in one of those Chinese component testers, in the past usually when a transistor is bad that Chinese tester would ID it as 2 resistors but I know transistors can be bad in different ways not only shorted, would you recommend a better testing method, perhaps a good affordable tool for this kind of tests?
I don't have a Variable Power Supply but I'd like to buy one if its worth it for this repair, does anybody know what's the Minimum DC I could use in order to troubleshoot this amplifier?
I'm trying to avoid using the whole 85 VDC.
Thanks!
I'm trying to avoid using the whole 85 VDC.
Thanks!
Oh well, just put this one back on the bench and still a mystery...
Its been almost 2 years and since then I have been reading and learning, In the meantime I have fixed other Adcoms GFAs including another 5800 and a 5500 which share a lot of its topology, but those have had faulty MOSFETs or resistors but this one everything seems OK and its behavior is really weird, sometimes the speaker output goes all 63 VDC positive and other times goes negative, one time even was fine but VDC started slowly increasing to 63 again, voltages from the power supply are correct, etc.
Any ideas???
Its been almost 2 years and since then I have been reading and learning, In the meantime I have fixed other Adcoms GFAs including another 5800 and a 5500 which share a lot of its topology, but those have had faulty MOSFETs or resistors but this one everything seems OK and its behavior is really weird, sometimes the speaker output goes all 63 VDC positive and other times goes negative, one time even was fine but VDC started slowly increasing to 63 again, voltages from the power supply are correct, etc.
Any ideas???
Additional troubleshooting Observations:
1. If I connect both of the +/- 70VDC all good, no DC voltage being leaked to speaker outputs nor to the preampfification area.
2. If I connect either of the +/- 85VDC separately everything seems to be fine.
3. If I connect both of the +/- 85 VDC that’s when it goes bananas, with or without the +/- 70VDC rails connected...
1. If I connect both of the +/- 70VDC all good, no DC voltage being leaked to speaker outputs nor to the preampfification area.
2. If I connect either of the +/- 85VDC separately everything seems to be fine.
3. If I connect both of the +/- 85 VDC that’s when it goes bananas, with or without the +/- 70VDC rails connected...
I've had issues with leaky protection zeners in the GFA-5802. Not the same amp, but it has similar protection zeners. They can get leaky if they take a static shock through the input cables, perhaps when plugging them in. In your amp that's Z1 and Z2.
Oh well, I de-soldered and checked every single component in the input area and re-soldered them back, now its -84VDC....
All right!!!
I de-soldered, tested, re-soldered and even changed some components that were a bit close to the tolerance limits, yeah, and that’s for the 1% tolerance resistors. After all that work I reconnected the channel assembly and same freaking thing...
Well then I decided to use 5 minutes of the KISS therapy and boom, turns out that the right channel has the exact same behavior when I connect it to the left side of the power supply and the left channel is perfectly fine when connected to the other side of the power supply, it has only 12 millivolts of DC Offset....
Jeeeezzzzz, will take a look at the PSU tomorrow, I bet it just a leaky capacitor or Zener diode.....!!!!!!
I de-soldered, tested, re-soldered and even changed some components that were a bit close to the tolerance limits, yeah, and that’s for the 1% tolerance resistors. After all that work I reconnected the channel assembly and same freaking thing...
Well then I decided to use 5 minutes of the KISS therapy and boom, turns out that the right channel has the exact same behavior when I connect it to the left side of the power supply and the left channel is perfectly fine when connected to the other side of the power supply, it has only 12 millivolts of DC Offset....
Jeeeezzzzz, will take a look at the PSU tomorrow, I bet it just a leaky capacitor or Zener diode.....!!!!!!
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oK!!
So last night I removed the power supply and again de-soldered every component from that left side and checked them, well only the ones on the regulated +/- 91VDC area, resistors, zener diodes, Transistors, voltage regulators, capacitors... all apparently good.... I have compared voltages with the other side and they all matched, nothing wrong there.
Well there was only 1 thing left to disassemble and analyze, yeah, the balanced input board I was really hesitant to do that because its a pain to remove but I said, I must because that thing has a couple of loops to ground so I did it, and YES, that was freaking it!!!!!
An open ground, see below.... JEeeeeezzzzzzz!!!!
So last night I removed the power supply and again de-soldered every component from that left side and checked them, well only the ones on the regulated +/- 91VDC area, resistors, zener diodes, Transistors, voltage regulators, capacitors... all apparently good.... I have compared voltages with the other side and they all matched, nothing wrong there.
Well there was only 1 thing left to disassemble and analyze, yeah, the balanced input board I was really hesitant to do that because its a pain to remove but I said, I must because that thing has a couple of loops to ground so I did it, and YES, that was freaking it!!!!!
An open ground, see below.... JEeeeeezzzzzzz!!!!
Congratulations ! That was a stubborn critter. I hope you clean off the flux after doing the work because I have
found it to be conductive and can cause faulty operation in high impedance nodes. It has happened to me.
Again Good Job !
G²
found it to be conductive and can cause faulty operation in high impedance nodes. It has happened to me.
Again Good Job !
G²
Thanks!!
Yes, once I re-solder everything I clean it with 99.9% Isopropyl Alcohol from MG Chemicals 😉