Integra DTR 50.5 Audio Output...Looks like a Sawtooth

Thread Starter

mohare

Joined Feb 11, 2019
2
Hello All,
I posted this on Audiokarma with no bites...hopefully someone here can help.
I have an Integra DTR 50.5 on the bench that was failing into protection mode immediately upon power-up. I found the problem (initial) with an open transistor Q5434 on the pre-amp surround-right channel (reference the attached schematic).
Problem is that particular 2SC2880-Y is no longer in production and I couldn't find an exact replacement in an SMD format. I wound up replacing it with a TH device just soldered to the board...#2SC3468.
The specs for the 2880 and the 3468 are attached.
Good news is, the receiver works and all channels are fine...except the SR.
Now the challenge:
Pushing 1Khz through the SR channel sounds like a saw-tooth signal (pic of waveform attached).
My question is: would the different parameters of the transistors cause this, or am I looking at another component issue. Problem is, with the configuration of the amp, I can't get to the devices to test without pulling the board so all testing has been passive.

Other notes: this preamp board is a bad design. Attached are some pics of broken solder connections and the back-sides of the SMD transistors are dark brown from heating...

Thoughts?

Thanks,
Matt
 

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abrsvc

Joined Jun 16, 2018
97
I see a lot of poor solder connections in the area too with one transistor (3 legged through-hole) part completely disconnected. Fix those as well. FWIW: My sub guide says that a 2SD1009 should work if you can find one of those.

Dan
 
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