HH Scott R75S : what type are these small square black polarized caps ?

Bert 1100

Super Member
Hi all,
I am starting on a restoration of an HH Scott R75S receiver.
In a few places like here in the tone board I see these small value (1uf and 2.2 uf) caps.
They are black, square and polarized. Are they electrolytics ? or more likely tantalums ?
I guess they are not films since they are polarized ?

IMG_2658.jpg

And an other question, there are quite a few green film caps, mostly 0.22 uf. Their casing is cracking around the top edge, see photo. Is it something to worry about, will it impact longevity ?
I guess as long as I'm doing the whole thing they will have to go. What do you think ?

IMG_2659.jpg
 
I'm restoring the exact same receiver (Scott R75s) and have the same questions. Did you ever find answers to them?

Is there anything else you learned from the restore?

Also, any ideas about the small diode shaped capacitors?
 
I'm restoring the exact same receiver (Scott R75s) and have the same questions. Did you ever find answers to them?

Is there anything else you learned from the restore?

Also, any ideas about the small diode shaped capacitors?
How are the weird caps represented on the schematic? The green film caps are probably fine, but no harm in replacing.
 
As far I see in the service manual, those black caps are most likely electrolytics and they are in signal path on that tone/preamp board and I'd replace them with some good quality electrolytics, Nichicon FG, Panasonic FC or similar audio coupling caps. You may even try to squeeze a film cap in there, but I really don't see a good reason to do that. To sum up, on that board you have C8, C108 (1uF 25V) and C3, C103 (2.2uF 25V) that can be replaced with same value caps and you can use higher voltage rating on them.
As for those cracked green caps, I would replace them as a precaution because the innards are exposed to air and contaminants and that could change their properties and it's really not worth the risk to leave them in there.

Good luck with the restoration!
Cheers!
 
if you are new to the recap business, then mark each, on the board, where the caps are with a
mark (white, color) for where the polarity is. follow the markings on the cap , not the stenciling
on the board. verify with schematic and understanding of the cap's role.

and buy non-polarized caps as a guarantee against wiring backwards. or films.
 
The black caps are probably stacked plastic film, the green chicklets metallized mylar. Both are reliable and stable.
 
Thanks everyone for your replies. I've searched images for old tantalums and found the diode looking ones. So I'll leave all of those little ones alone.

-I've seen reference in various discussions here to types of transistors and diodes known to be likely failures. Is there some compiled list of component #s or styles to check?
-Also, If I replace that green metalized mylar cap in the picture above on the driver boards, I assume that I can just switch the one with the gap in the coating rather than replace them all. That is, from my limited knowledge, I don't see anything in the schematic that requires them to be precisely matched.

Thanks again!
 
Another odd cap in this receiver. .22/12v. Looks like a ceramic, but black. Not polarized. Are there 12v ceramics?
Located between B and E on a transistor that provides a regulated 13v output.

IMG_0461.JPG
 
check whether it's .22 or 22. pull and measure if you're going to replace. verify
through schematic, parts list, or cheapy mega328 tester.
 
Ok, as part of a recap I pulled those square box polarized caps and subjected them to destructive testing. My best read of their contents is that they are some kind of tantalum capacitor. Two metal plates, and some crumbly metallic contents. Very small. Definitely not a micro sized electrolytic of some sort--no foil layer that I could see.

The caps were still dead on for capacitance, but I don't have the ability to test other things. So I just replaced them while I was there.

Here's a close up pic for those who might know better:
IMG_0617.jpg
 
Great info guys, thanks ! I now have two R77S I need to restore for the same person that gave me the R75S to do...
 
Great info guys, thanks ! I now have two R77S I need to restore for the same person that gave me the R75S to do...

Great! I'd love to see some pictures of the inside of an R77s. I'm also interested in how the switch handles the 10000uf filter caps. (As near as I can tell, everything is the same as R75s except higher secondary on transformer and double the size on the supply filter caps. I was sorely tempted to bump mine to 10000uf.)

I'm finishing up a thread on recapping an R75s here. It's my first time at this so my decisions are fwiw, but there are comments by folks more knowledgable and most importantly, some links concerning errors/likely misinterpretations in the service manual.
 
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Ok, as part of a recap I pulled those square box polarized caps and subjected them to destructive testing. My best read of their contents is that they are some kind of tantalum capacitor. Two metal plates, and some crumbly metallic contents. Very small. Definitely not a micro sized electrolytic of some sort--no foil layer that I could see.

The caps were still dead on for capacitance, but I don't have the ability to test other things. So I just replaced them while I was there.

Here's a close up pic for those who might know better:
View attachment 1201102

What did you replace them with? I hope film, and if not, then UKL series from Nichicon. Tants are known for low-leakage characteristics.
 
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