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Harris Vintage console issues

S

SFM-Ptgal

Yesterday, without my intervention, my Harris Stereo 80 console started to have strange movements on the left VU meter with no audio feeded onto it. I swapped the left and right audio output card and the strange movements went to the right VU meter.
Then I swapped the "faulty" output card with the Monition one what I got was steady VU meters but a very noisy pot when I turn it.

Hints are welcomed...

Thanks!

Pedro
 
frankberry said:
There is probably a bad (leaky) coupling capacitor in the defective module.
Click to expand...

Thanks Frank! Is leaking typical on elect. capacitors or also on others? I'm asking this because there 're just three elect. capacitor on the module.
After a search on the internet pictures from what I saw I don't have apparent leakage on the caps :-\

Now I noticed that I don't have that card schematics. I must search for it on the internet or ask for support here :(
 
Electrically leaking, as in, there's DC current on the wiper of that potentiometer, because the capacitor is leaking.
Hard to go wrong changing all of them, but if the board's not too complex you should be able trace out which one is in the signal path.

ALL electrolytic capacitors have leakage. It is true and unavoidable. It is their chemical nature.
We have accepted this flaw for the past 75-80 years since they give such high capacity in a small space.
Oh, and they're cheap.
 
Tom Wells said:
Electrically leaking, as in, there's DC current on the wiper of that potentiometer, because the capacitor is leaking.
Hard to go wrong changing all of them, but if the board's not too complex you should be able trace out which one is in the signal path.

ALL electrolytic capacitors have leakage. It is true and unavoidable. It is their chemical nature.
We have accepted this flaw for the past 75-80 years since they give such high capacity in a small space.
Oh, and they're cheap.
Click to expand...

I'll give it a try. Since they're only 3 it'll be easy.
I didn't describe the noise affecting the VU meter/PGM output. It sounds like a rumble where sometimes the meter reaches peaks @ 0db but most of the times the needle swings between -20 and -10. It's almost inaudible. It's the same rumble I hear when I use the faulty module on the monitor output and turn the pot.
 
Sounds like something is oscillating--sure sign of dried up capacitors. Especially if the board has been in storage for a while, it may work OK when first powered up, but then the coupling and power supply caps dry out a little more, values change, and nothing seems to work quite right. Just "shotgun" all the electrolytics and you will solve multiple small problems. You don't need a schematic, though it would be nice, just some pre-planning.

1. Buy a "Sharpie,"--that is, an indelible ink marking pen, and mark the + ends of the capacitors on the circuit boards;

2. If at all possible find some solder wick*(Trade marked name) or similar type de-soldering braid. I like Radio Shack's braid over the real solder wick, but I would imagine that's hard to find near you.

3. Accumulate the capacitors you need. If you can't find the exact value, go up slightly. For example, older equipment often used 200 MFD caps--a hard value to find now, but 220 MFD will work just as well. You can also substitute higher voltage for lower voltage caps--and may have to. Some of those older axial caps were physically much bigger than what you will find from the parts suppliers now.

4. A 25 watt pencil soldering iron should work just fine.

Go slow and have fun.
 
With gear of that vintage it would just be a better bet to shotgun the entire unit and replace ALL the electrolytics at once. Be careful though, just because something is "new" doesn't mean it's "good".

I picked up a couple of Belar FM monitors (FMM-1/FMS-1) that I'm going to be using for a school radio station. I replaced nearly every cap in the main unit and I started to burn up the power supply. Come to find out one of the brand new caps were leaky.

I now test every one BEFORE I solder it in place.
 
That model is notorius for losing caps. If the sound on the air or in the monitors is lacking low end, that's another sign that it's time for a re-cap. Caps not only leak voltage, they also lose their capacity and depending on their location in the circuit, their ability to pass low frequency audio. One of the first symptoms is trying to keep the VU meters balanced. Songs with a lot of low end will often show different left & right indications whille a higher pitched female voice may show better balance...or vice versa depending on where those master gain trim pots are set. If you're keeping that console, invest in a supply of caps...you'll use 'em.
 
100 Uf at 50 v are common

25 Uf can be replaced with the more common 22 UF

640 UF can be replaced with the more common 680 uf.

Wouldn't hurt to use 35 volt or even 50 volt caps instead of 25 v. Suspect you will have plenty of room.

But go ahead and get all the caps you'll need for the board. Probably shouldn't cost all that much, and it is very likely that there are other caps waiting to fail. Otherwise you will be doing what my one cat likes to do--chase your tail!
 
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