Hey everyone, got a question about a Kenwood KR-4140. This was my dad's when he was in college in the 70's, and he gave it to me when I was in school about a decade ago. Put it to some good use, but accidentally killed it in 2010 and I'm trying to get it up and running again to surprise him.
The short version: It began blowing fuses and I think the main problem is a capacitor that needs to be replaced, but having a second opinion would make me feel a lot better before desoldering anything.
I think it's this capacitor, located on the underside of the KR-4140:
The black tube on the right (hard to see - the capacitor has a reflection) is the fuse.
The schematic from the service manual:
It's the capacitor that goes between the on/off switch and the fuse. As I understand it, at time=0, the capacitor acts as a "short", taking the full flow of current from the wall outlet. As time goes on, the capacitor transitions to looking like an "open", slowly sending current to the transformer, allowing it to power up gracefully. If the capacitor has begun to fail towards a short, this would be sending the full brunt of the current from the wall plug through the fuse for far too long, causing it to pop.
Without removing the capacitor out of the circuit, I have no way of testing it. Looks fairly rounded on the ends though, which is why it is suspect #1. I also can't see the other side to see what's marked (does it have a polarity? No markings and the schematic being two straight lines makes me think no but I have no idea). Don't have much currently in the way of testing gear, just a digital multimeter.
The service manual has it listed as C301 - Oil Impregnated, 0.01uF, +100%, -0%, part number CP052W103P. From what's printed on it I am assuming the AC800V means it can take up to an 800 volts of AC power. For other capacitors I have seen, the (M) printed normally means +-20% of the printed capacitance, but the specs listed in the manual seem to differ.
Looking online for parts, I couldn't find anyone selling this particular capacitor, and the closest I could find on Digi-Key was the Cornell Dubilier Electronics (CDE) 940C30S1K-F (.01uF +-10%, 3000VDC, -55°C ~ 105°C, ESR of 60 mOhm, Axial, film Polypropylene (PP), Metallized, High Pulse, DV/DT capacitor). Digi-Key (and other sellers) have it marked as 750VAC, but I found a datasheet that only has it listed at 500VAC. I ordered it (only $3, no big loss if it's wrong) to see what VAC was printed on the side - only has the 3kVDC listed.
Is this an ok swap, or am I about to cause major problems? I'm in the USA, so only expect 120VAC from the wall, and will probably have the KR4140 on a surge protector to try to keep major surges from getting to it. From what little other work I have done replacing capacitors in old equipment, the usual rule I follow if I can't find an exact replacement is to have a higher voltage rating, not lower. But I've only ever replaced electrolytic capacitors in logic circuits dealing with DC voltage - nothing in direct contact with house/plug-level voltages and currents.
I know this may not fix it and I may be barking up the wrong tree, but it was the first step. I just didn't want to swap it out and cause any more damage or have to clean up a capacitor that has exploded.
I have another receiver (Pioneer SX-737) that I opened to check out the capacitor it has in the same position. It has a disc capacitor (maybe ceramic? looks like a giant Spree candy - but is much larger than any other ceramic capacitor I've ever seen) marked MR .01 +100% -0% 125 VAC CM2 5D. I know it's a different receiver, but seeing it only has a 125 VAC capacitor in a similar position makes me feel better about the 750/500 VAC one I found.
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The longer version on how the problem started:
The problem started after a roommate blocked a good chuck of the top vents with a cable box and DVR. Not trying to make excuses - it was entirely my fault for not catching it and changing the layout. He said something about weird behavior on the speakers, but I couldn't replicate it. A few weeks later, after watching some football all Saturday with the stereo cranked fairly loud - I leave the room for a phone call and when I get back into the room (about 15 minutes) the roommates say the problem was happening again, but they left the stereo on so I could hear it. Room was silent, so I asked what was up. They said it was cutting in and out and just went silent right before I came into the room and stayed that way. When I was about 5-10 feet from the KR-4140, I could smell burning electronics. Can't remember if any lights were still on the front panel, but I quickly killed the power and began unhooking the speaker wire. Pulled the fuse out and it was broken.
A few days later I found a package of fuses from the local hardware joint. With the speakers still disconnected, no A nor B selected, no headphones, no input, put a fuse in - lasted about a second before it popped. Took off the outer wood case and opened up the top of the metal case. Put in another fuse, turned it on. Maybe a second goes by and it pops. I don't see anything spark, and I don't see any smoke. Went over the components I could see and visually everything looks fine. It was close to finals, so I put it to the side to look at later - where it has sat for years.
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Thanks a bunch for any help / thoughts you may have. I'm always nervous when doing something like this for the first time and even more so with this since it has sentimental value to someone else.
The short version: It began blowing fuses and I think the main problem is a capacitor that needs to be replaced, but having a second opinion would make me feel a lot better before desoldering anything.
I think it's this capacitor, located on the underside of the KR-4140:
The black tube on the right (hard to see - the capacitor has a reflection) is the fuse.
The schematic from the service manual:
It's the capacitor that goes between the on/off switch and the fuse. As I understand it, at time=0, the capacitor acts as a "short", taking the full flow of current from the wall outlet. As time goes on, the capacitor transitions to looking like an "open", slowly sending current to the transformer, allowing it to power up gracefully. If the capacitor has begun to fail towards a short, this would be sending the full brunt of the current from the wall plug through the fuse for far too long, causing it to pop.
Without removing the capacitor out of the circuit, I have no way of testing it. Looks fairly rounded on the ends though, which is why it is suspect #1. I also can't see the other side to see what's marked (does it have a polarity? No markings and the schematic being two straight lines makes me think no but I have no idea). Don't have much currently in the way of testing gear, just a digital multimeter.
The service manual has it listed as C301 - Oil Impregnated, 0.01uF, +100%, -0%, part number CP052W103P. From what's printed on it I am assuming the AC800V means it can take up to an 800 volts of AC power. For other capacitors I have seen, the (M) printed normally means +-20% of the printed capacitance, but the specs listed in the manual seem to differ.
Looking online for parts, I couldn't find anyone selling this particular capacitor, and the closest I could find on Digi-Key was the Cornell Dubilier Electronics (CDE) 940C30S1K-F (.01uF +-10%, 3000VDC, -55°C ~ 105°C, ESR of 60 mOhm, Axial, film Polypropylene (PP), Metallized, High Pulse, DV/DT capacitor). Digi-Key (and other sellers) have it marked as 750VAC, but I found a datasheet that only has it listed at 500VAC. I ordered it (only $3, no big loss if it's wrong) to see what VAC was printed on the side - only has the 3kVDC listed.
Is this an ok swap, or am I about to cause major problems? I'm in the USA, so only expect 120VAC from the wall, and will probably have the KR4140 on a surge protector to try to keep major surges from getting to it. From what little other work I have done replacing capacitors in old equipment, the usual rule I follow if I can't find an exact replacement is to have a higher voltage rating, not lower. But I've only ever replaced electrolytic capacitors in logic circuits dealing with DC voltage - nothing in direct contact with house/plug-level voltages and currents.
I know this may not fix it and I may be barking up the wrong tree, but it was the first step. I just didn't want to swap it out and cause any more damage or have to clean up a capacitor that has exploded.
I have another receiver (Pioneer SX-737) that I opened to check out the capacitor it has in the same position. It has a disc capacitor (maybe ceramic? looks like a giant Spree candy - but is much larger than any other ceramic capacitor I've ever seen) marked MR .01 +100% -0% 125 VAC CM2 5D. I know it's a different receiver, but seeing it only has a 125 VAC capacitor in a similar position makes me feel better about the 750/500 VAC one I found.
------------------------------------
The longer version on how the problem started:
The problem started after a roommate blocked a good chuck of the top vents with a cable box and DVR. Not trying to make excuses - it was entirely my fault for not catching it and changing the layout. He said something about weird behavior on the speakers, but I couldn't replicate it. A few weeks later, after watching some football all Saturday with the stereo cranked fairly loud - I leave the room for a phone call and when I get back into the room (about 15 minutes) the roommates say the problem was happening again, but they left the stereo on so I could hear it. Room was silent, so I asked what was up. They said it was cutting in and out and just went silent right before I came into the room and stayed that way. When I was about 5-10 feet from the KR-4140, I could smell burning electronics. Can't remember if any lights were still on the front panel, but I quickly killed the power and began unhooking the speaker wire. Pulled the fuse out and it was broken.
A few days later I found a package of fuses from the local hardware joint. With the speakers still disconnected, no A nor B selected, no headphones, no input, put a fuse in - lasted about a second before it popped. Took off the outer wood case and opened up the top of the metal case. Put in another fuse, turned it on. Maybe a second goes by and it pops. I don't see anything spark, and I don't see any smoke. Went over the components I could see and visually everything looks fine. It was close to finals, so I put it to the side to look at later - where it has sat for years.
------------------------------------
Thanks a bunch for any help / thoughts you may have. I'm always nervous when doing something like this for the first time and even more so with this since it has sentimental value to someone else.