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Car stereo output stage blown

Pyle PLRG23 I had the unit out, on the bench, troubleshooting no FM lock. AM was fine. I had power/ground connected to the plug, which also carries the speaker circuits. These are female connectors.The radio was on, at min volume. I did not have speakers connected. During initial testing with a logic probe in the tuner section, the radio shut off. I found high current draw in the power supply, and turned it off immediately. On checking, the radio would not power up, and drew 10A from the supply. I determined the monolithic stereo output chip (TDA-burn) was dead short to ground. The heatsink was quite hot. Q: Could the chip fry from no load connected? I'm certain I didn't short it at the plug, and wasn't even in the output stage with my tests. JR

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Reply to
JR North
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Under normal circumstances, I would have said absolutely not, but strangely, today, I was discussing exactly this with a colleague, who installs and repairs car entertainment kit for a living. I was picking up a large Sony AV amp from his shop for repair, and he said that it had symptoms of output failure, and he thought that this was most likely because the owner did not use the front channels on it, only the surround ones, so did not have any load connected to those fronts. I expressed doubt at this, telling him that the general rule of thumb was that semiconductor outputs didn't like shorts, and valve outputs didn't like opens. but then he told me that he sees car radios all the time, that have the sides blown out of the output ICs, caused by the speaker connections being left open, when the owners use external blaster amps, driven from low-level line outputs, rather than from the speakers.

So, based on that, and the fact that he is generally good at what he does, and knows what he's talking about, I would have to revise my opinion of your question, and say "yes, very possibly ... "

Arfa

Reply to
Arfa Daily

Getting my start in mobile audio some seeming centuries ago, I would say yes it is possible. I was taught to always load the outputs regardless. I feel for you. I've spent many hours righting accidental wrongs and wrongs that in your case appeared secondary to the cause for repair and weren't justified as billable.

Reply to
Meat Plow

Greetings..

Just a crazy question but, WHY were you in there with a "logic probe" in the first place?

Granted, after repairing HF, VHF and UHF radios for years in the amateur service I realize the computerization of radios these days, but I'm just curious.

Do you have electrical schematics for this unit? Ultimately a service manual for this type of situation?

No?

Simple solution, IF you want to pay for correcting the issue - back to the certified manufacturer repair depot. Otherwise, scrap or shotgun guesswork (and associated expense) without schematics, voltage levels, waveform diagrams and alignment procedures.

Cheers, Mr. Mentor

Reply to
dBc

I'm no car stereo expert, but- Common failures in car stereos (besides shorted outputs) are vibration induced opens in solder joints, particularly through boards connected at 90° . These are easy to find with simple tools. Thats what I was doing initially, hoping for a quicky. This isn't the sort of radio one invests too much time in. JR

Reply to
JR North

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