Author Topic: This car stereo got a bit toasty...  (Read 905 times)

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Offline ELS122Topic starter

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This car stereo got a bit toasty...
« on: August 23, 2023, 09:43:31 pm »
Doesnt seem like the thermal protector worked, or maybe it started carbon tracking, although I doubt THAT much current would flow with just 12V trough carbon
Even the solder shows signs of melting... probably leaded solder. the radio probably is from the late 90s, the IC looks like it was first used around the mid 90s
It uses a LA4445 output amp, so I guess those are good for up to 200 degrees.

The amp still worked until the board crumbled when I bent the output IC a bit to read what it was.

I wonder if those capacitors are good  ;D
« Last Edit: August 23, 2023, 09:49:23 pm by ELS122 »
 

Offline tom66

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Re: This car stereo got a bit toasty...
« Reply #1 on: August 23, 2023, 09:53:06 pm »
I've seen a transistor amp IC similar to that (linear amplifier, class AB topology) fail in a similar manner.  In my case it was a Sanyo STK amplifier chip, the amplifier chip ran very hot indeed but still worked ok, but after about 10 minutes the left channel would go very distorted.  I suspect the high side transistor for the left channel had become leaky, such that as it got hotter and hotter it got leakier and leakier.  This led the output voltage to slowly climb, leading to more dissipation in the speaker and STK chip, though it still retained some modulation.  It didn't seem like that amp had any DC protection so presumably the speaker could easily be destroyed and/or cause a fire should the amp chip continue to fail in this manner.

 

Online Circlotron

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Re: This car stereo got a bit toasty...
« Reply #2 on: August 23, 2023, 10:04:17 pm »
That’s a LOT of electrolytic caps!
 

Offline ELS122Topic starter

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Re: This car stereo got a bit toasty...
« Reply #3 on: August 23, 2023, 10:54:52 pm »
That’s a LOT of electrolytic caps!

Quite typical for those "early" output IC's, caps for output coupling, caps for negative feedback loop, caps for bootstrapping, and caps for the input coupling, then also output coupling caps for the cassette preamp, caps for it's input coupling. etc. Since it's single supply.
 

Offline Bud

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Re: This car stereo got a bit toasty...
« Reply #4 on: August 26, 2023, 01:02:06 pm »
The IC may oscillate if capacitors dried out, and generate heat because of oscillation.
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Online DavidAlfa

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Re: This car stereo got a bit toasty...
« Reply #5 on: August 26, 2023, 03:51:22 pm »
Classic symptoms of a metalhead having a daily journey from work!  :-DD
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