Sanyo DS20425

[Zenith26kc20]

Had a good fight this morning with this Sanyo. It came in with intermittent audio and the board under the LA4525 audio IC was darkened. This IC is an 8 pin DIP and uses the pc board for heat sinking. I changed the IC and found out that it was roasting in seconds.
After checking for oscillation and open electrolytics, nothing showed. I checked DC offset at the input, no problem. When I checked the output to the speakers (both) the offset on each was around 3 volts. BOTH output electrolytics were shorted! I removed one and then noticed the trouble! The electrolytics are installed backwards at the factory! Checking with a meter for proper voltage revealed they truly were backwards! Replacing them and installing them correctly makes the IC run cool to the touch!
And another note... the ESR meter was tricked by them being shorted. They weren't "puffed" either!

[freakaftr8]

Wow! From the factory! Thats insane

[soundman2]

That could have been nasty! Electrolytics being installed reverse polarity are bad news

[Zenith26kc20]

After doing this set I think I figured it out. On these Sanyo sets, the ones that failed (now three of them!) they are played loud by the customers. It seems the electrolytics are tolerant up to a certain voltage even if backward. Once played loud, the voltage goes up and breaks them down.
At least I know what's up now with this problem!

[ctc17]

Shouldn't those be non polarized? Not that Sanyo would want to spend the extra penny per set or anything

[Zenith26kc20]

The output caps block the DC from the output IC from getting thru to the speakers (about 1/2 the B+).
They are polarized and should have about 6 volts on their positive teminals.
They are 16 volt caps so they eventually break down then kill the output IC.