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My KR-6200 is a hummer (sort of)

Lol, typically, yes, capacitance matters! However I don't usually see huge changes in capacitance, just pretty large increases in ESR and leakage.

I suspect with those little computerized low voltage testers that capacitance numbers are not all that accurate on old caps, Slow charging due to dry electrolyte and high leakage during charge could show up as increased capacitance when in fact the capacitance is low and the leakage is high.

Obviously vented caps will occasionally test near normal specs, but there is no way they are actually working correctly.
 
HPMguy said:
Lol, typically, yes, capacitance matters! However I don't usually see huge changes in capacitance, just pretty large increases in ESR and leakage.

I suspect with those little computerized low voltage testers that capacitance numbers are not all that accurate on old caps, Slow charging due to dry electrolyte and high leakage during charge could show up as increased capacitance when in fact the capacitance is low and the leakage is high.

Obviously vented caps will occasionally test near normal specs, but there is no way they are actually working correctly.
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Interesting discussion guys. Now that I've got the proper multimeter, I hooked up the caps I pulled and tested for capacitance. This is what I got, let me know if I did it right:
DSC00479.JPG DSC00480.JPG DSC00481.JPG
 

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I've never used a DMM for a capacitor tester other than to watch the resistance change as they charge. I like my little cheapo meter since I can also test transistors with it. Out of circuit, of course.
 
HPMguy said:
I've never used a DMM for a capacitor tester other than to watch the resistance change as they charge. I like my little cheapo meter since I can also test transistors with it. Out of circuit, of course.
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So, Based on your post #46, the reading in the second photo above of 1.096 for the cap rated at 1000 meanssssss anything?​
 
The little crappy testers offer convenience. They are not accurate, but they are certainly close enough.

I test parts before it goes in...because Rod Elliott says its a good practice, and it's saved from mistakes on several occasions. Wrong values, bad components, wrong alignment, bad markings. Most my fault, some were not.

I test most components after they come out. I find it fascinating to see what happens to a cap after 40 years and I look for patterns so I know why I’m doing things.

a good capacitance meter is at top of my wish for my bench.
 
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Okay, I'm throwing this open for anyone to respond - should I proceed with freeze spraying those 4 transistors shown in post #59. This will be my first attempt at freeze spraying!
 
Turned on receiver this morning, Humming began 5 minutes later. Got the Freeze It and shot this transistor. Humming stopped immediately:Trans531.png

I know enough to refrain from concluding this is the culprit and should be tested/replaced, so any knowledgeable opinions welcome!
 
Well that one could certainly do it. But like you, i'd be cautious.

Screenshot_20210531-100045~2.png

Wait for the hum to come back and shoot another to see what happens. Or refreeze this one and be very careful to control the spray to avoid hitting other parts.

Another option could be to buy all the suspect semiconductors. It will be cheaper than a second round of shipping.

How are your soldering skills? You can pull and test that one pretty easily.
 
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Looks like a KSD526 is where I would start as a substitution for the 2SC1060. Other thoughts on better selections?

When you order, don't forget the thermal grease and mica insulator.
 
Well, receiver's been on now for 3 hours, and hum hasn't returned. I'd like to pull and test this one. I got good soldering/unsoldering practice recapping power supply board. Looks like unscrew the bracket and desolder two prongs - what will I be testing it for?
 
There will be three leads.

Here is another sticky for you to read:

https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/

Echo Wars posted it and it is a great resource. Yours is intermittent, so might test good when cold.

Personally, I'd just replace it. You said it was hot, and that kills a device over 50 years. The replacement is under $1. But still test it, 'cuz knowing how to test transistors is the next step in vintage geek evolution.
 
One of those cheap little computerized testers would be good here, as it can give you more information than a DMM.
 
Ran receiver over 7 hours yesterday, 30 minutes, then 20 minutes today and no hum. Meanwhile, checked out the foil side of the 2sc1060 transistor and it only has two legs soldered to the board. The middle leg is just a stub. Mouser has a KSD526Y for less than a buck - its middle leg is the same as the other two. If I were to install it would I leave the middle leg alone or maybe trim it?
 
That's not right. All three legs are supposed to be connected. Is there a solder pad that's no longer connected?
Screenshot_20210531-100045~2.png
 
OK. The collector is the metal flange. See something new every day.

upload_2021-6-1_21-23-59.png

The replacement KSD526 should have the flange as the collector, too, and should be connected to the center pin. I'd verify it with your meter before clipping off the center leg. You should not use a mica insulator. I suggest checking to be sure that, on the existing unit, the center pin has continuity with the heat sink.
 
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It is interesting. The KR-6200 schematic at HFE has a different power supply board than the service manual at HFE. X00-1240-10 vs X00-1150-10.
 
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Some folks 'round these parts use NTE only when there is no other option. There is an opinion that the NTE component sourcing and spec matching is inconsistent and you never quite know. Probably ok for a voltage regulator but one never knows.
 
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