Radio cleaning and pre-emptive cap. repair?

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Mattax

Mattax

Just the facts, ma'am
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I removed the top cover of the radio to do some light cleaning. So far just lightly brushing the dirt and vacuuming it up. And maybe that will be it.
There looks to be a hairline crack on the 50 microF capacitor.
Any idea what that is made of?
I'd like to weld or epoxy that up - assuming its just plastic aging and not a sign of internal failure.
Not seeing any leaking or bulging.
upload_2020-5-5_18-29-42.png


upload_2020-5-5_18-30-39.png


Model 236
upload_2020-5-5_18-31-54.png
 
67Dart273 said:
I would just replace it. That would be an electrolytic, capacity is not that critical, you want at least but not less in capacitance, and at least the rated operating voltage, Last I knew, Mouser Electronics would fill small orders, and has always been helpful.
Click to expand...
Yes they still accept small orders - just ordered some terminals from them yesterday.
If a replacement can be put in, that sounds like the better route to go.
It looks like there may be good access to the board with the bottom removed.
 
FWIW Turns out its not a capacitor. It's two stacked together. Other side has 500UF on it.
 
That's the AVC filter and Amplifier feedback capacitor. I replace with two single electrolytic caps. Yes, that crack is common and the AVC capacitor is bad.
 
Somewhat related is if your volume control isn’t as variable anymore? I might take the cover off mine to poke around but the minimum volume on it is quite loud on mine. Im assuming it must be something with the volume rheostat/potentiometer that isn’t working well anymore?
 
H22A4 said:
Somewhat related is if your volume control isn’t as variable anymore? I might take the cover off mine to poke around but the minimum volume on it is quite loud on mine. Im assuming it must be something with the volume rheostat/potentiometer that isn’t working well anymore?
Click to expand...
That seems likely but not my area of knowledge. Maybe vacuum and a little DeOxit 5 worked around in.

This radio was working pretty well. I just happened to have it out because it made it easier to get to other stuff. When I saw how dirty it was inside, I opened it up to clean. If I hadn't taken the top off I'd never known there was a crack on that stacked cap. That's not to say it was working perfect - but it certainly recieved the stations audibly.
 
billccm said:
I never remove the PCB for repair or capacitor replacement. The radio in that video had an open transistor buried deep down and I replaced with the PCB mounted.
Click to expand...
Thanks. If you're willing to walk a beginner through this, I'd give it a try. Do I just identify the connections by physical location? And will I need to wick or suck the excess solder off the leads?
 
Newer caps are much smaller, you could likely place the old body over them to be stealth.

47 uF, 470 uF are standard values. Electrolyic caps have a high +/- 10 to 20% tolerance, those will work fine. I can see 3v, on one, ? on other side. Replacement should be same or higher. Typical replacement voltages might be 6.3V, 10, 25 ... I would look for automotive rated with temp rating of at least 105C or better, for long life.
 
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I use solder wick and add some rosin flux while desoldering. The large CAN CAP takes some finesse and a soldering gun. If you can wait a few days I might have the schematic and printed circuit board drawing of component connections I can send you.
 
Yes. No rush. This was a detour. I'm fixing and slightly modifying the wire harness right now.
I'm OK with leaving the can cap by the power supply. if it fails later, replace it then. That should be be pretty obvious when it goes!
That one is Bendix 2092983 0708
Also might be stacked?
900 MFD 16 V DC
700 MFD 16 V DC
CAN CM NEG
108166417 85*C

The black one with the crack on the top (AVC filter) is labeled
iei
500 UF-3V +
209224[64 ?]
6642
50 UF -3V +
911
[There's also a vertical yellow stripe facing forward]
 
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halifaxhops said:
Yes take the excess off. Solder wick will be the cheapest for you Matt
Click to expand...
Have a small roll of 1/16 or 1/8.
For small irons a 40 Watt electric Weller and a butane powered portable with a selection of tips.
 
Back to working on this.
Since I don't have the knowledge or info on which lead was for which capacitor I was poking around the internet for more manual with the info. SAMS Technical publishing has their old "Photofact" manuals available as downloads. That had the connections identified on the schematic so the locations could be figured.

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We'll give desoldering and removal a shot later this morning.
 
Mattax said:
Back to working on this.
Since I don't have the knowledge or info on which lead was for which capacitor I was poking around the internet for more manual with the info. SAMS Technical publishing has their old "Photofact" manuals available as downloads. That had the connections identified on the schematic so the locations could be figured.

View attachment 1715577918

We'll give desoldering and removal a shot later this morning.
Click to expand...

That went pretty well.
As I had thought, only one ground for the stacked capacitor.
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Here's the work station including an almost never used solder gun.
Not in the photo is a combo magnifying glass and desktop lamp.
upload_2020-8-14_11-45-55.png


Followed the procedure here
How to Use a Desoldering Wick

Bent the leads up as I went along. Bending up the last one, the other two moved and the cap practically fell out.
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Melted a little bit of the conformal coating.
Any suggestions on resealing after the new caps are installed? Nail polish? or something more specifically for the job?

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One more observation.
The + symbols line up with the lead for their respective capacitors, and the stripe with the ground lead.
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Don't worry about the coatings. I have recapped hundreds of car radios and never recoated.
 
One thing that helps (me at least) with any rework is the ABILITY TO ADD MORE FLUX. There are lots of fluxes available, you want one meant for electronics, and Kester is / was the "go to" people. Unfortunately many big suppliers, such as Kester, only offer such things as flux pens--which are OK as far as they go, and then gallon or 5 gallon production sized.

Another thing to keep in mind is that there is a VAST difference in PC boards. Years ago when I worked for the Motorola shop, we built a large repeated system..........using multiple receivers on one freq at different locations, then the audio outputs are sent to a device called a "voter" which decides which receiver audio to send to the transmitter for repeat

ANYway, some of the receiver strips needed repair and modifications. They were TERRIBLE quality cheap grade PC boards, and attempting to remove components resulted in the LIFTING OF A PAD.

You want a large enough/ hot enough iron to heat the work up quickly without sitting there for a long period, and transferring heat through the work area, causing damage.
 
Should I twist the ground leads together or solder individually?
I'm leaning toward the latter.
 
Not sure it matters whatever is convenient. Don't twist them until you stress them
 
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