QUAD FM4 odd behaviour - UK Vintage Radio Repair and Restoration Discussion Forum

chartz2 · 1st Feb 2020, 11:09 am

Hi all,

On this example, the yellow buttons wouldn't trigger the TMS1000 at all, or erratically so. Sometimes one button would work, just like that, and one moment later it would do nothing.

I realized that when I touched pins 2 and 3 with my finger, looking for bad solder joints, everything worked as it should. New joints did nothing, unfortunately.

Then I tried to spray a little contact cleaner over those pins and it worked fine until the liquid had evaporated (repeatedly).

I therefore connected two small caps (330 pF) between pin two and GND and pin 3 and GND.

Now, stations can be selected and memorized fine as they should.

Explanation please?

Thanks!

chartz2 · 1st Feb 2020, 4:05 pm

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barrymagrec · 1st Feb 2020, 6:06 pm

I`d be looking at the power rail for the chip and local chip decoupling.

chartz2 · 1st Feb 2020, 6:24 pm

Quote:

Originally Posted by barrymagrec

I`d be looking at the power rail for the chip and local chip decoupling.

Thanks.
However I can’t see any PSU decoupling cap locally. Where should I look?

1st Feb 2020, 11:09 am	#1
chartz2 Pentode Join Date: Jan 2010 Location: Burgundy, France. Posts: 125	QUAD FM4 odd behaviour Hi all, On this example, the yellow buttons wouldn't trigger the TMS1000 at all, or erratically so. Sometimes one button would work, just like that, and one moment later it would do nothing. I realized that when I touched pins 2 and 3 with my finger, looking for bad solder joints, everything worked as it should. New joints did nothing, unfortunately. Then I tried to spray a little contact cleaner over those pins and it worked fine until the liquid had evaporated (repeatedly). I therefore connected two small caps (330 pF) between pin two and GND and pin 3 and GND. Now, stations can be selected and memorized fine as they should. Explanation please? Thanks! Last edited by chartz2; 1st Feb 2020 at 11:16 am.

1st Feb 2020, 4:05 pm	#2
chartz2 Pentode Join Date: Jan 2010 Location: Burgundy, France. Posts: 125	Re: QUAD FM4 odd behaviour

1st Feb 2020, 6:06 pm	#3
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,561	Re: QUAD FM4 odd behaviour I`d be looking at the power rail for the chip and local chip decoupling.