Kr-2300 suddenly only buzzing

[Gertjan90]

I'm having a stroke of bad luck, I fear.

I turn on my little kr-2300 and nothing but buzzing comes out.
It was working fine just yesterday.

I've only had this receiver for a couple of days and apart from some cleaning, didn't do anything to it.
The sound is great and much more powerfull than 14WPC would suggest.

But now, there is no sound coming through the speakers at all, and with my headphones on I can only hear a monotone buzz coming through both channels. The buzzing doesn't change with volume, tone, inputs..
All fuses are intact.

So far, I've checked the output transistors and they are fine, as well replaced the 1000µF caps, but no change.
Solder joints all look good.

Any thoughts on what might be causing this?

It's a damn shame because I really like the look of this receiver.

 

[Gertjan90]

It worked fine after cleaning for days, I only scrubbed the face plate and dusted it with some air.

No sound with or without the case, although the humming got quieter when I swapped out the big caps for new ones. Might be coincidence, though.

I'll go hunting for some loose wires.

 

[mbz]

Measure the dc Voltage (mV/) between the left (red&lack) speaker posts. Repeat for right channel.
I'd disconnect the spkrs not wanting to risk damage. Use cheap headphones if needed. Both channels
does point to power supply. Are you comfortable taking measurements on a live unit?

 

[Gertjan90]

Today I had a bit of time to do some quick tests.
I tested the diodes in the power supply in circuit and most check out with a reading of 0.78 forward and OL 'reverse'.
But D11 got 0.78 forward and 1.64 reverse. Could this be the culprit?
I have some time tomorrow, I'll take D11 out to test it propperly.

I can do simple tests on a live unit, but my hands arent that steady..

Vdc on outputs was as following:
Left : 1.5V(!)
Right : 0.78V

 

[mbz]

There is an alternate path (Re85) when measuring De11, so incircuit measurement
will be misleding.

Prefer to use clips rather than probes when doing incircuit measurements

Yeah the L&R dc voltages are way too high, however I just noticed that it
is a cap coupled design so the voltages need to be read with a load attached
to the speakers. You need to make up two 7-8 ohm resistor, at least 1Watt, prefer
5W, 10W ok. Connect the resistors acoss each speaker outlet/red&black left, red&black
right channel. Set volume to minimum. Measure voltage across left then right outlets.

 

[Gertjan90]

I frankensteined some decent 8ohm resistors and tested again for Vdc, but I couldn't get a reading..
Looked like AC going through the resistors, fluctuating between 0.01 and 30mV.

Diodes D4, 7, 8 and 11 are all ok, I checked them out of the board.

C45 has been replaced with a 6800 cap I had lying around, but still no sound. The noise went way quiter, though.

Also no losse or touching wires to be found.

Anyone any more ideas?

All help appreciated.

 

[Gertjan90]

Hi, thanks for the suggestions! I'll take those out and test them as well over the weekend. Hopefully I find something, I have those transistors lying around.

 

[Gertjan90]

oops double post

 

[Gertjan90]

Hi guys,

I'm glad to say that that my little KR-2300 is back up and running.
QE22 ended up being bad. It looked pretty burned when I took it out, but still passed the diode test.
Replacing it fixed it. Or it might have been C56, I replaced that one for good measure since I don't have a reliable way to test caps. Wasn't shorted though.

I have a mixed bunch of caps and transistors in there now that I used for testing, will be replacing them with proper ones soon.

I do wonder if the 14WPC it's rated at is accurate, it sound way more powerfull. My Yamaha CR-200 is 16wpc but sounds quite a bit weaker.. (still very nice, though)

Anyway, big thanks to you guys, you were a great help.
If you ever end up in Belgium, I'll buy you one of our famous beers!