Soundstream lilwonder 4.480 filter problems

[nemiers]

Hi all, first post but cant figure this out on my own.

Amp is quite old Soundstream lilwonder 4.480, I was using it as first 2 channels driving speakers and 3;4 channels small pioneer shallow mount sub.
Problems started as sub was loosing signal, checked wiring and filter switch and could not find any problems, after cycling filter switch many times sub seemed to work in LPF. But after a while sub burned and amp was in protect mode.

So I replaced small power transistors and two D988 transistors, amp is out of protect I was happy, but before putting it back in car decided to test it. First two channels are ok. But the 3. and 4. channels seem not to work in LPF, HPF, FULL modes, it works only in BPF, but is crazy loud, gain to minimum, same settings as channel 1,2 except 1,2 running at FULL. 3. and 4. channels are too loud and distorted.

Where to look for problems? I have tested all diodes marked with Z. And small transistors 2sd667 and 2sb647 at channel 3,4 side.
What else to test?

Thanks a lot for any help.
Adding pics of amp:

[Perry Babin]

Do you have a scope or any way to trace the signal through the amp?

Try to get a schematic diagram from Soundstream.

[nemiers]

Originally Posted by Perry Babin

Do you have a scope or any way to trace the signal through the amp?

Try to get a schematic diagram from Soundstream.

Unfortunately all I have is multimeter.
When amp is running with input audio signal, normally channels 1 and 2 by measuring at output speaker side with multimeter set to AC it is around few volts. But channels 3,4 Set to BPF are around 20V with gain set to minimum.

Emailed soundstream and asked for schematics, lets see what they say.

Thanks.

[ian33]

Base on the pics i see lots of cold solder joints

[ppia600]

/\ Would be a good idea to check for cold solder joints, start with the devices clamped to the sink then move on to larger devices on the board then work your way down. That appears to be an asian built soundstream, I didn't realize the lil wonder wasn't built in the US.

[nemiers]

Bad soldering could be all my job
Resoldered all fets, to get amplifier out of protect mode. Replaced shorted ones.

Got an answer from soundstream:
''The schematics are only available to authorized dealers. ''

[Perry Babin]

Measure the DC voltage on the output pins of each of the 8 pin op-amps. Does any op-amp have more than 0.1v on the output pins (1 and 7)?

Place the black meter probe on one of the non-bridging speaker terminals. Place the red meter probe on the point where you need to measure the voltage.

[nemiers]

Originally Posted by Perry Babin

Measure the DC voltage on the output pins of each of the 8 pin op-amps. Does any op-amp have more than 0.1v on the output pins (1 and 7)?

Place the black meter probe on one of the non-bridging speaker terminals. Place the red meter probe on the point where you need to measure the voltage.

Took measurement from both sides, in case I understood it wrong:

[Perry Babin]

That's not an op-amp. See attached. Check all similar.

[nemiers]

Originally Posted by Perry Babin

That's not an op-amp. See attached. Check all similar.

Sorry for that!

Most of them have no voltage on pins 1 and 7,
but 3 of them had:

One had 0,38V on pin 1
Two 0,12V and 0,18V on pin 7

Thanks!