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Marantz 2275 Power Amp Board Need Help Troubleshooting

Have you already adjusted the P800 output to 35V? Are your P700 left and right outputs, both set at 10mV?

I had a weird left channel in my 2275 too, until those three voltages were set correctly.
 
Thanks for sharing your info. I have not made any adjustments or measured voltages yet. Are you adjusting those voltages for biasing? I should have done some voltage checks before removing the power amplifier circuit board. I will check for voltage at the connector to the power amplifier circuit board right now.

All I have done to the receiver so far is replace the volume potentiometer that was broken when I bought the receiver, clean the other potentiometers along with switches and recapped the power supply board which solved the issue with the relay taking a long time to engage on powering up. I also began yesterday testing the transistors on the power amplifier.
 
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After recapping the power supply, you should adjust the supply voltage per the service manual - after powering up on dim bulb tester to make sure you have no shorts. If it passes, remove the DBT, plug into wall, and adjust power supply voltage to 35V. But don’t power up if you have any wires or boards loose that could short to something. If you have one amp completely out, you can adjust bias (idle current) and DC offset on the good amp - again, per the service manual. But if the relay is clicking, and you have zero sound in one channel, bias and offset aren’t the problem. If they were, you would either get no relay click or distorted sound - but not zero sound. I’m not sure what you have so far, but you need a Dim Bulb Tester (you build it yourself) to test for shorts every time you power it up after making changes. And, of course, you need a service manual - available in the AK database.
 
I found this video helpful. If you skip to about 37:30 - he talks about the power,bias, and offset, though he measures the bias at a more difficult spot than necessary.
 
In an attempt to do the easy things first, I just pulled the connectors to the power amp circuit board, turned the amplifier on and measured DC voltages from each pin on the connector to ground. One of the pins measured about 35 DC Volts. The voltage measurements on the working power amp connector were similar. I was thinking they would be AC Volts but measuring for AC Volts the results were small fluctuating values so I assume the power supply is rectifying the voltage and power amplifier circuit boards receive DC voltage.

I think this is more evidence that the issue is either a bad component or connection on the power amp circuit board or a knob or switch not working properly. What do y'all think?

I wish I had a variac but honestly I haven't left the house much lately and just feel lucky I had the thermal compound being thankful for what I do have.
 
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I’ve still never quite gotten straight the symptoms. You know the left amp is good, I think. So, if you run the left Pre into the left amp (normal), I assume left channel works. If you jump from right Pre to left Main, do you get good sound through the left amp? If yes, then it’s likely the right amp, and you are on the right track checking transistors on that side. Also, if yes, you can eliminate the preamp and controls from the suspects. So that is very important information to have straight. While a variac is nice to have in certain circumstances, it’s not necessary here. But you do need a dim bulb tester. — and somewhere along the way, go back and follow the service manual instruction to measure the power supply DC volts. It’s probably OK, but it needs to be right and it’s simple to check. So be sure you have it right. Page 9 in the service manual under Audio Adjustments.
 
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Steven Tate said:
I’ve still never quite gotten straight the symptoms. You know the left amp is good, I think. So, if you run the left Pre into the left amp (normal), I assume left channel works. If you jump from right Pre to left Main, do you get good sound through the left amp? If yes, then it’s likely the right amp, and you are on the right track checking transistors on that side. Also, if yes, you can eliminate the preamp and controls from the suspects. So that is very important information to have straight. While a variac is nice to have in certain circumstances, it’s not necessary here. But you do need a dim bulb tester. — and somewhere along the way, go back and follow the service manual instruction to measure the power supply DC volts. It’s probably OK, but it needs to be right and it’s simple to check. So be sure you have it right. Page 9 in the service manual under Audio Adjustments.
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That's correct. The left amp is good and I have been listening to the left amp through the left speaker all day today with no problems. If I jump from right Pre to left Main using RCA cables, I get good sound through the left amp but it is the right stereo track I hear through the left speaker. Connected normally and with the mono buttons engaged I can hear both stereo tracks through the left speaker. I can get no sound through the right speaker output. Just to test, I plugged the left side power amp connector into the right side power amp circuit board and heard some low distorted music through the left speaker.
 
All of that is as it should be. Your problem is the right amp, so it needs to be traced down. Have you diode tested those outputs yet?
 
Steven Tate said:
All of that is as it should be. Your problem is the right amp, so it needs to be traced down. Have you diode tested those outputs yet?
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It just turned nighttime here and I am about to start testing the output transistors now since I have been trying to enjoy the outdoors as much as possible during daylight hours. What is the best way to clean up the old heatsink compound? 90% Isopropyl alcohol and a nylon brush?
 
I completed testing the 2SB554 PNP transistor and the results met requirements. I am going to reinstall it and then remove and test the other transistor. Is the other transistor NPN or PNP?
 
I now have completed testing on the other SMT D424 95ES NPN transistor and it also met requirements. I am going to reinstall the transistor trying not to get thermal compound on the transistor pins so there is still a good electrical connection.
 
You have checked the most likely culprits, and they seem to be OK. At this point, if I'm sure the amp is the problem, I start pulling the other transistors and checking them one at a time. But being long distance, I can't be sure I haven't missed something. Have you checked right speaker to make sure it is good? I also would hook up the right amp and do a few voltage measurements and compare to the left just to make sure the board is getting full power through the connectors. Also need to know for sure that the input to the amp is working. On the 2275, one way to do that is move the left amp board to the right position. The possibility that the signal isn't getting past the protection relay is also in the mix. Did you replace the relay? It's work, and compared to the real experts, it's probably not the best way to diagnose, but those are the things I would be trying at this point.
 
[QUOTE="Steven Tate, post: 13936865, member: 240223"The possibility that the signal isn't getting past the protection relay is also in the mix. Did you replace the relay? It's work, and compared to the real experts, it's probably not the best way to diagnose, but those are the things I would be trying at this point.[/QUOTE]

Tapping on the protection relay with a wooden spoon or other insulated tool will usually reveal poor relay contacts.

Tom
 
Steven Tate said:
You have checked the most likely culprits, and they seem to be OK. At this point, if I'm sure the amp is the problem, I start pulling the other transistors and checking them one at a time. But being long distance, I can't be sure I haven't missed something. Have you checked right speaker to make sure it is good? I also would hook up the right amp and do a few voltage measurements and compare to the left just to make sure the board is getting full power through the connectors. Also need to know for sure that the input to the amp is working. On the 2275, one way to do that is move the left amp board to the right position. The possibility that the signal isn't getting past the protection relay is also in the mix. Did you replace the relay? It's work, and compared to the real experts, it's probably not the best way to diagnose, but those are the things I would be trying at this point.
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I did not replace the relay, just the electrolytic caps on the power supply board. The current issue was happening before I recapped the power supply board.

This morning swapped left and right speakers to check for a speaker issue and both speakers work, thankfully. I was planning to record Voltage measurements on the Power amp board comparing them to measurements from the working amp board side and finish cleaning push switches.

That plan has changed because now when I plug in the amp board I worked on last night, the relay on the power supply circuit board will not engage. When I unplug the amp board the relay engages and I can listen to music through the working amp side. What did I do??? I put a very thin layer of thermal compound, do I need to use more?
 
The thickness of the compound would not be a factor. This is when you need a DBT to instantly see if you have a short. If you do, you have to go back and check your work looking for shorts, pinched wires, etc. of course, the amp wasn’t working in the first place. I’m surprised it came out of protection with the amp plugged in anyway.
 
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