Sony TA-FB920R no left channel

[diif]

Hello, I am looking at a Sony amp for my neighbour.

After reading this thread https://www.badcaps.net/forum/showth...highlight=sony I removed the boards and resoldered the relays. The crackling has now gone, but i am still left with sound only out of the right channel.

With headphones plugged into the amp i get sound in both channels so i am guessing its something to do with the main board ?

The big heatsink on the right gets warm but not the one on the left which stays cold.

Could anyone offer me some assistance please ?

[budm]

Re: Sony TA-FB920R no left channel

Service manual:

[diif]

Re: Sony TA-FB920R no left channel

Excellent, cheers budm.

[diif]

Re: Sony TA-FB920R no left channel

I located the problem, it was the two big MOSFETS fitted to the heatsink. I replaced both on both sides.

However i also noticed a damaged resistor R520.

In the Sony service manual it lists this part as critical for safety and only to be replaced with the part number specified.

It's part number is 124940511. 100 5% 1/W small carbon resistor.

Any idea why it states it has to be the exact part ? I can find them delivered for about £10 !!! for one resistor. If it has to be then i will pay it, but it seems very excessive for a tiny resistor.

thanks.

[Tube_Dude]

Re: Sony TA-FB920R no left channel

I located the problem, it was the two big MOSFETS fitted to the heatsink. I replaced both on both sides.

However i also noticed a damaged resistor R520.

In the Sony service manual it lists this part as critical for safety and only to be replaced with the part number specified.

It's part number is 124940511. 100 5% 1/W small carbon resistor.

Any idea why it states it has to be the exact part ? I can find them delivered for about £10 !!! for one resistor. If it has to be then i will pay it, but it seems very excessive for a tiny resistor.

thanks.

Use any 100 Ohm 5% 1/4 W fuse resistor... It's there only to avoid parasitic oscillation of the output Mosfets.

[diif]

Re: Sony TA-FB920R no left channel

Cheers Tube Dude, I'll stick one in tomorrow.

[diif]

Re: Sony TA-FB920R no left channel

Thank you budb and Tube Dude, one happy neighbour, and i've learnt some stuff in the process.

[Tube_Dude]

Re: Sony TA-FB920R no left channel

Cheers Tube Dude, I'll stick one in tomorrow.

So the SONY is already running?

[Longbow]

Re: Sony TA-FB920R no left channel

After reading this thread https://www.badcaps.net/forum/showth...highlight=sony I removed the boards and resoldered the relays. The crackling has now gone, but i am still left with sound only out of the right channel. With headphones plugged into the amp i get sound in both channels so i am guessing its something to do with the main board ?

Good photos and problem description. I'm just wondering why you skipped the step of taking some preliminary voltage and resistance measurements around the output stage? Maybe you just forgot to mention it.

[diif]

Re: Sony TA-FB920R no left channel

Thanks Longbow

This has been the first amplifier i have looked at for repair. I didn't do any of the checks you mention as was unsure of what i would be looking for.

I tested for voltages after i had the manual i was kindly provided as i felt a bit more confident in what i was looking at. They went all the way up the middle of the main board and i had tested the diodes and rectangular white resistors ? i figured it must be the mosfets.

I think the burnt resistor was due to me as the mosfets are held on with bent legs and big blobs of solder. I took Tube Dude's advice on the resistor and now i get lovely sound in both channels.