Sherwood Newcastle R965 Amp Board Repair Help Needed.

Thread Starter

Banthors

Joined May 19, 2022
31
I am working on repairing my uncles R965 Sherwood receiver which let out the smoke on the front left amp board rail after he spilled a small amount of coffee on it. The resistors on the front left track burned up along with 2 capacitors and a Ceramic Dual Emitter Resistor and all the transistors blew out as well. I ordered replacement parts for everything and tested and it produced very bad audio but it was working. Wanting to check if my replacement parts were bad I used the original transistors from another rail as they are all the same across the amp board. I left all the replaced resistors and the 1 electrolytic cap as the replacements but swapped a orange cap from the other rail. This made a huge improvement on the audio but at higher volume it still produces static/distortion. Im looking for help at what to look into next as i have tested all the resistors ohm values and they are all very close to the other rails. I will include the schematic and the pictures of the board/transistor heatsink array. The main problem I need to fix is the bad audio. I still will need to source replacements for the rail I borrowed from.

List of parts replaced
2SC2922 - Turned out to be a fake clone. Need to source a good one
2SA1216 - Turned out to be a fake clone. Need to source a good one
C3423x2
A1360x2
A1859A
C4883A
Resistors Various Ohms
Dual Emitter Resistor
2 Caps 1 Electrolytic 1 Polypropylene
 

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Dodgydave

Joined Jun 22, 2012
10,361
From the diagram , can you measure the voltages around the transistors Q211 to Q216 and compare them to the working channel when you have it assembled.

I would remove any debris from the pcb first and give it a good cleaning with isopropanol.
 

Thread Starter

Banthors

Joined May 19, 2022
31
Forgive me as this is a learning experience for me. Is it best to check base emitter collector legs or just checking voltage going into any places around the board making sure they match? I am assembling the amp board and mounting it back to the heatsink and i will post back with readings.
 
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Thread Starter

Banthors

Joined May 19, 2022
31
Power rail B+ and B- is stable 54.5 Volts DC. I will check the transitors on the outside now. How do you check voltages on the inside transistors? there is no way to safely probe them while live? @Dodgydave
 
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Thread Starter

Banthors

Joined May 19, 2022
31
Could only check the bottom transistors safely. All the transistors on the bottom row match up to the values of the other tracks.
While i was checking the B+ and B- On the plug itself. I accidently crossed the B+ and B-. It let out a very loud pop and arc but after checking it again it is still reading 54.9V DC stable.
Edit: I just realized am i supposed to be checking while the unit is on or off. I think you meant to test with unit on standby right or on?
 
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Thread Starter

Banthors

Joined May 19, 2022
31
Standby
B -3.3V DC
Q211 0 0 0
Q212 0 -3.3V DC 0
Q213 0 0 0
Q214 -3.3V DC 0 - 3.3V DC
Q215 0 0 0
Q216 0 -3.2V DC 0
Matches up with all the other tracks
 
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