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SC815 HU repair questions - dead front channels

bgpzfm142

crossmember
Joined
Dec 25, 2013
Location
Launceston, Tasmana
I hope to resurrect the dead front channels of a SC815 tape/CD/radio unit.

Here's the audio driver board from it.

XA7ibpBl.jpg


IC391 (top left of board) and IC591 (top right) appear to be the two audio power ICs for
this unit. IC391 appears to cover the front tweeters, while IC591 looks like it powers up
the front and rear speakers for both left and right channels. The PCB is helpfully marked
on the trace side with letters indicating what goes where on the two big main cable
connectors.

That's actually helpful, since I've been unable to locate a circuit diagram for this unit after
exercising much google-fu.

However, neither the two ICs don't have any type numbers visible. Well, not without
removing the heat sink shrouds, which are soldered to the PCB.

What much googling did discover was how there are two possible manufacturers of these
units - Alpine or Mitsubishi - and these ICs are either a pair of TDA1558Q units, or a pair
of TA8221L ICs.

Does somebody reading this have a circuit diagram for one of these beasts?

Who else has repaired one of these things?
 
Okay, so the polishing of this um yeah right continues.

I got an SC813 unit (the model without the inbuilt CD player) pillaged it for its audio driver board, and plugged it into the SC815.

The dead front channels returned to life. Yay.

But the CD wouldn't load. Hmmm.

t9uadwXl.jpg


Whooops! There's a few missing components. The ones which perform the in-unit CD function are missing from the SC-813's board.

SC813 board is top of pic; darker coloured board is the original SC815.

KxW7JQAl.jpg


So at least the problem has been isolated to the audio driver board.

Without a circuit diagram, I going to take a punt and replace both of the TDA1558Q audio ICs on the SC815's board, and then we'll see if it's fully restored.
 
Fixed!

Replaced both of the TDA1558Q audio ICs,and all the channels now work.

Getting the heatsinks off of the PCB was a bit of a challenge, since whoever assembled the thing decided to give the little tangs an extra twist before soldering 'em on. I discovered the quickest way to extract each dead TDA1558Q was to remove the heatsink first, then desolder the IC.

YMMV, but I prefer these old units to the wizz-bang modern units which have only one potentiometer to do a multitude of functions. Having separate bass / treble / fader controls is better for me.
 
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