Sony str-k502p Amp quiet channel.

[Toasty]

Re: Sony str-k502p Amp quiet channel.

Price checks:

STK350-230 < $8 - Buy from reputable distributor. Wary of fakes!
uPC2581V < $18 - Same " " " "

MN2488* ** < $6 Sony #: 8-749-010-25
MP1620* ** < $6 Sony #: 8-749-010-26

* make sure these are the original Sanken transistors. ASK!
If they continue to fail, you probably will have to go with *real* Sony parts @ $15 a pop.

** replace as a pair per channel, not individually


http://www.bdent.com/

http://audiolabga.com/ - Has the real Sony MN & MP listed. No stock.



Toast

[Toasty]

Re: Sony str-k502p Amp quiet channel.

[NxB]

Re: Sony str-k502p Amp quiet channel.

Ok, finally had time to work on this. Replaced an MN2488 and MP1620 pair. Doesn't seem to have done it. The STK gets hot, and the NECs get hot too after the relay click.

Rather than replacing those, I looked around and found a small PNP transistor that gets hot immediately. It is Q692 and it is on the -B SW along with Q691. I have to pull both of them out of the circuit and test them.

[NxB]

Re: Sony str-k502p Amp quiet channel.

Q691 the 2SC1815 is shorted on, ordering some and we'll see if it does the trick.

[NxB]

Re: Sony str-k502p Amp quiet channel.

Nope, still nothing. Now it goes into protect.

[bcstedt]

Re: Sony str-k502p Amp quiet channel.

Any update? I'm working on a similar Sony receiver with a similar problem.

[bcstedt]

Re: Sony str-k502p Amp quiet channel.

OK, looks like the caps close to the upc2581v get cooked by the heat. Three are giving an open reading on the ESR meter (10v, 100u, 85c) and those were almost in direct contact with the backside of the upc2581v.

You might also see the board turning brown under the chips where it has been baked by the heat. How much would it cost Sony for a couple tiny heatsinks or at least some 105c rated caps?

[Longbow]

Re: Sony str-k502p Amp quiet channel.

Here is a hint that might help out. When output devices fail (usually they short) many other semis in that circuit can also smoke because everything is direct coupled. So, the other transistors in that channel are the first suspects. Resistors should also be checked in that amplifier channel. But specifically it is good practice to replace the current sensing resistors in the failed channel-the ones that are in the source or emitter leg of the device. These parts will be in the area of .1 ohms, very low resistance. Replace them, because they usually increase in value. They might not be open or burned, but the value goes up, causing the circuit to go into current limiting. That's it.