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Kenwood KRC-478R no audio

G.E.C

New Member
I have a Kenwood cd changer car tape there is no audio, i have changed the audio ic but there is stil no audio, i have also sent it to kenwood agents and they failed to repair it any suggestion.:confused: GUYS CAN ANYONE HELP WITH SCHEMATICS
 
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btcg

New Member
I have a Kenwood cd changer car tape there is no audio, i have changed the audio ic but there is stil no audio, i have also sent it to kenwood agents and they failed to repair it any suggestion.:confused: GUYS CAN ANYONE HELP WITH SCHEMATICS
You say you've already replaced the audio output ic?

Then, you sent it to an authorized Kenwood service and they failed to repair it?

What did they say? If they could not find a problem, check your speaker/wiring.

If your audio output ic was shorted, it's possible that the line that provides the vcc for the ic has an open resistor, and no voltage is getting to the new ic.

What I've done in the past when I had trouble finding a schematic was to cross the audio output ic to a ECG or NTE equivilent, and find out what pin provides the vcc of that device, as it will be the same as the original. From there, you can trace it back by following the foil pattern. If that's the issue, it'll be a low value resistor, most likely, that's open.

The pin out info from the cross is quite useful. If it is getting voltage, you can check to ensure that it's getting input, etc.

This at least, gives you something to try.
 

G.E.C

New Member
Kenwood Krc-478r

CHECKED THE Vcc THE VOLTAGE IS THERE, I DID NOT CHECK THE INPUT TO THE IC
 
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mister_e

New Member
Most of these unit use TDA7386 (or variant of). If any speaker, speaker wire, have a leak or short to ground, this will send the unit to protect mode (kind of.... just no sound on ALL speaker to protect the output IC). Check speaker wiring with an Ohmeter to GND first.

It's a fairly old unit though.. possible that the problem is elsewhere...

Are you testing it in your car or on a bench?
 
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G.E.C

New Member
I am testing on the bench, i have found that the TDA 7400D advanced car signal processor has got input from fm, am, cd, tape i have feed the input from this chip to another amp there is audio, but on the output pin of the chip i have no audio and cannot get this chip in SA, any sugestion where i can get it.
 

btcg

New Member
GEC,Sounds like you're on to the problem. But don't get tunnel vision.

Example:In the early 1990's, I was repairing a Zenith TV with a 9-147 vertical module. The symptom was a shrunk picture. We normally stocked several 9-147 modules (the replacement for the 9-92 module). But we were out. So we got a rebuilt from a company named PTS. We didn't repair the modules in those days, they were about 10 dollars, so it wasn't worth our time. So I put the PTS module in: same symptom. So I spent the next several hours looking elsewhere. On a hunch, I opened a repaired set and took the 9-92 module out of it, and put it in the other set. The result? I had full deflection. PTS had taken in a module for rebuilding with the exact same problem we had, and had failed to repair it (it turned out to be the transistor before the oscillator, the vertical gain transistor, I believe).

The lesson? You may have replaced the output, but if you replaced it with a bad chip, you're no better off.

Keep that in mind.
 
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