"Entertainment page #1"
January/February 2006 (10,006PH)
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Question :                                  How many true continents are there on our planet?                                      (answer at bottom of page)

Articles from "Rick's Workbench"

Tale of interest no.1

The SHARP entertainment unit from hell:

A good friend recently inherited a SHARP, entertainment unit and rang me about fixing it for him.

The only fault (apart from the quality of the equipment) was that the lamps illuminating the tuner display had expired.

My friend tried using a torch to see the display but got sick of that pretty quickly. I agreed to have a look at it for him.


The unit appeared one bright day, along with a smaller AKAI that wouldn’t play CD’s.
My friend had bribed me with a bag of spuds and some beetroot to repair these units.
The next day I decided to tackle the beasts. The small unit was relatively easy, a clean with alcohol and cotton buds to
the laser lens and interlock sensor, got it up and running.


Suitably enthused, I then tackled the big beast.
After removing a million screws and various parts of the horror, I finally got to the display board and the offending lamps.
Both were in series and blown, and I had to do a bit of juggling with the meter probes to measure the voltage applied to
the lamps.
Whilst I was doing this I heard a sickening “pop”, followed by a familiar smell that comes from IC’s bursting.
I had a good look around all the boards in this thing but didn’t see anything obvious.

"Oh well!" I thought "I might as well get the lamps replaced and the see what works and what doesn’t".
After a lot of mucking around, I settled on two 12v lamps, under run, to give a suitable display colour.
Now to test the beast…     I hooked up some headphones and was greeted with a loud hum in one channel and nothing
in the other.

Well, now I knew where to look….     The output stage was the likeliest place to start.
That’s when I spotted a tiny sliver of solder, that had deposited itself on and between some wire links on the power amp
I determined later that the short was between the left channel output and the negative supply rail. “Oh bother” (or some
other polite term) I said, and rang up my parts supplier with a request for an
STK4132II output chip.
This was on a Friday morning in between a series of intense thunder storms….                     They didn’t get back to me.


A sudden wave of dread came over me..  "That chip is probably obsolete and oh darn," (or again some other polite term),
"what am I going to do now?"
I got onto the 'net and searched for the part number of the chip.                A circuit appeared with some data on the chip.
It turned out to be a 20w per channel amp, nothing all that special.
I then worried about it all weekend and planned a possible option involving LM1875 amplifiers which I knew were easy
to get, and went about designing a circuit board for them.
I was that desperate to solve my little mishap!

I rang the parts supplier on Monday morning and they confirmed my worst fears…     The chip was no longer available!
In the back of my mind I knew I had seen something with a similar chip.  Then I remembered…     My Sony amplifier had  
After removing it from the tangle of cables that connected it to my audio and video equipment, the lid was removed     
YES.....    It had a similar looking chip but with a different number on it!                My heart sank…      So near yet so far.
It was an

I guessed the amp was about 40w per channel so I got onto the 'net and looked up the part number.
I got the complete data sheet for it and as it turned out, it was rated at 55W per channel.         
What really caught my eye on the data sheet was that this entire series from 6 to 60W were pin compatible.

I then checked the circuits for both chips and yes, apart from minor differences in the feedback circuits (involving tone    
controls being added in one circuit), they were the same.

I wondered what would happen if I replaced the blown one with the STK4192II ?   Would it work?   I thought it might  

but was worried about the much reduced supply voltages stuffing up the chip's internal biasing and causing distortion.  
Give it a try?    Why not.   I had got nothing to lose!

The big test!    Yes it did work!     No distortion was evident to my ears (which I judge as pretty good at hearing
distortion of audio signals).    I breathed a sigh of relief.           My friends entertainment unit was up and running again,,  
thanks to an old Sony amp (that ironically, was given to me a few years previously by the same friend), and,
the internet!

The moral of this story is to be VERY careful with older equipment using these STK type chips.
It was just sheer luck that I had a compatible part available, and at no cost (so far).
The SONY amplifier is now waiting to be resurrected and put back into use.

Has anyone got a spare
STK4192II ?


Till next time.

All rights for this article belong to "Rick's Workbench" in Tasmania


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Answer to above question :  North America, South America, Antarctica, Australia, Africa and finally Eurasia (incorporating Europe, Russia & Asia).
                                            (Europe is strictly a peninsula).                                                                                                                                       
                                            India can be classified as a sub-continent as it is only part of Eurasia because it has crashed into it.                                  


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