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

 

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

 

Thanks this was useful info, I had a similar issue with my DTR50.5 going into current protect, but a different SMD transistor (a 2SA1200-Y) blew on the class A board (Q5046) and on the SBR channel rather than SR. I also replaced with a non-SMD transistor (a 2SA2140) that I stole from the preamp stage of a parts Onkyo amp. The amp works fine after replacement, I don't have the sawtooth wave issue. It looks like the Q5434 transistor could be a matched pair with the Q5444 in the case posted here which would mean possible issues if just replacing the one.

Something I found useful was a compatible cable with the sockets for the class A board which lets you easily test each channel one at a time.

I found the +/-15v regulators were out of spec on my amp (and had no visible thermal grease from the factory), replacing these appears to have fixed an issue with the 4k HDMI inputs not connecting (not sure what else could have fixed it) and that part of the amp is not putting out quite as much heat. Be mindful if replacing that both share the same heatsink and so need to be electrically insulated from it (the stock regulators are in fully insulated package)

It seems like with this amp the voltage regulators cook the SR and SBR channels, that combined with cooling fan that turns on only in response to output heatsink temp (on an amp that runs pretty cool in that regard) causes a lot of thermal stress, especially as the amp can heat cycle even if left turned on all the time due to switching between L and H amp states based on usage/volume. Am currently considering mods to improve the cooling/temp management.