2270 Sudden Distortion Issue

[grunge]

First of all, I did a full recap/restore of my 2270 a little over three years ago, and it's been my main unit ever since -- I have probably used it nearly every day for the last three years and it has worked beautifully. No issues to report... until now!

It's worth mentioning I am getting ready for a big move, and was just listening to music through my 2270 via a bluetooth receiver hooked up to the aux input while I was packing up the rest of my stereo components. I had just unhooked my turntable maybe an hour prior to this issue, although I'm not sure that had anything to do with it. I left the room for a moment, and just as I did, the music cut out and I heard some of the loudest, bassy distortion/humming I have ever heard. I ran back into the room, turned off the unit and disconnected all power as quickly as I could. Then I unhooked the rest of my components and opened the top cover to check it out. Without disassembling any further, there was no visible damage, but the right heat sink was incredibly hot -- far hotter than the left. I'm also not completely certain I heard the relay click off when I cut the power, but I can't be sure.

I have not tried turning anything back on yet -- I wanted to come straight here to see if anyone had any immediate ideas as to what could have caused this, what the problem might be and what kind of fixes this might need. As it's been a few years since I last had to work on this receiver, I'm just a bit rusty.

Thanks in advance!

 

[grunge]

Update: with the cover still removed, I reconnected power to the 2270 (no components or speakers) and briefly switched it on -- the relay took much longer to click in, and as soon as I switched on the power, there was a crackling sound coming from the board attached to the right heat sink, as well as a faint plastic-y odor. I turned it off pretty much immediately after hearing the relay click.

Does anything come to mind as to what the culprit might be here?

Thanks again!

 

[JD Harvey]

Wow! Man, that sucks! I'm not very knowledgeable, but don't turn it back on and unplug. If it were me, I'd remove the heatsink from the right channel and inspect the parts for discoloration (brown or burnt looking). I bet it won't take 2 minutes before you find the issue. Blown resistor, cap, diode, transistor? Post pictures when you see the blown part. Just my .02

 

[dankik]

...there was a crackling sound coming from the board attached to the right heat sink, as well as a faint plastic-y odor.

Here is the board on the right heatsink, it's the P750 Power Amp board (R-channel).


Here are the components on that board. Which, if any look toasted? There are also two transistors mounted to the heat sink, be sure to check those also.

 

[grunge]

Thanks all for the replies -- unfortunately (or perhaps, luckily), nothing looks fried on P750. I was remembering however an error I made during the restoration those years ago where I damaged the original output transistors attached to the heat sink -- after replacement with the proper parts, it worked like a charm. I was able to test for this issue by first removing the blown output transistors (which, to my memory, showed no physical damage), and then powering up the unit to listen for a relay click.

Just now, I removed the output transistors, which, again, showed no physical damage, and reluctantly plugged in the 2270 and fired it up -- no crackling, and a relay click almost immediately! I'm not holding my breath, but I'm going to order a replacement set of output transistors and see if that does the trick. Would be such an easy fix if so.

Hopefully I'm able to make the repair before moving -- will post an update when I get the replacement parts!

Thanks again.

 

[dankik]

You might need to order some new mica insulators and thermal compound for the new transistors also. If you have made a dim bulb tester (DBT), now would be a good time to use it to test the new transistors.

If you have a multimeter or DMM, here's a quick way to test the transistors:

 

[JJCalvillo]

What @dankik said.

Thing is output transistors going bad only a couple of years after replacement usually means something up the line on the amp board is causing a problem.