I had my Quadra 840AV (which I recapped and had working) plugged in for some time without using it and randomly decided to turn it on today. Unfortunately it did not turn on. After checking the PSU, I found out I was not getting anything from 12V, only from the 5V rail. After a few minutes, I removed the PSU and plugged it back in the electrical outlet and it suddenly started making a weird sound and soon after smoke started coming out. I quickly unplugged it. I opened it up but on first instance I didn't see anything out of the ordinary really. I later turned it back on and one of the MOVs blew up.
I had no experience with PSU repairs whatsoever so I was stupid enough to just replace the varistor that blew up and a couple of suspect capacitors and turn it on! Sparks again, a bang, and the mains tripped. The second varistor blew up as well as the fuse. I later learned that to work more safely with PSUs, I should have made a series bulb tester/current limiter. I then started learning more about PSU repairs and did some more troubleshooting on the PSU. I found at least one TRIAC that had shorted, and after removing both main caps so that I could get access to the blown varistor, I found out one of them, the one close to the blown varistor, was showing capacitance in the nF instead of the rated 1200uF.
After ordering some more components and waiting patiently, I replaced the TRIAC, replaced the main capacitors, replaced the MOVs, jumpered the fuse temporarily as I didn't have a replacement at hand, and I also created a light bulb current limiter. Note that I couldn't read the MOV markings anymore, so I ordered these https://nl.mouser.com/ProductDetail/...r983RJeg%3D%3D, but now I'm wondering if they are the correct ones. Unlike the usual case where they are placed before the bridge rectifier, these are placed next to each of the two main capacitors. I plugged the PSU in the current limiter and turned on the current limiter switch. Nothing blew! The light bulb was dim. I checked the voltage on the main capacitors and it read about 200V. Then I decided to attach the fan, and after turning on, I saw sparks and smoke somewhere in the area of the main capacitors (top left corner in the picture), but I couldn't tell which component got burned! After that, the light bulb was full on...I'm not sure if the fan caused the issue or it was just a coincidence. Also, I would expect some short, but measuring the resistance between the AC leads show something like 200k Ohm, so now I'm not sure what is wrong. I checked all diodes on the main side and they all seem to give correct values. The bridge rectifier also does not seem to be bad. Does anyone have any tips? The only thing I can think of now is to start removing components and measure them off circuit. As a last resort I'm thinking of buying one that is working and cross reference the circuits.
I uploaded an image of the PSU. I annotated the TRIAC with green, the bridge rectifier with red, the MOVs with blue. Also note: I found solder on windings of the component in yellow (is this a transformer?). Not sure if that came from me, but I was able to remove most of it with a solder wick. Not sure if this could be a potential issue.
I had no experience with PSU repairs whatsoever so I was stupid enough to just replace the varistor that blew up and a couple of suspect capacitors and turn it on! Sparks again, a bang, and the mains tripped. The second varistor blew up as well as the fuse. I later learned that to work more safely with PSUs, I should have made a series bulb tester/current limiter. I then started learning more about PSU repairs and did some more troubleshooting on the PSU. I found at least one TRIAC that had shorted, and after removing both main caps so that I could get access to the blown varistor, I found out one of them, the one close to the blown varistor, was showing capacitance in the nF instead of the rated 1200uF.
After ordering some more components and waiting patiently, I replaced the TRIAC, replaced the main capacitors, replaced the MOVs, jumpered the fuse temporarily as I didn't have a replacement at hand, and I also created a light bulb current limiter. Note that I couldn't read the MOV markings anymore, so I ordered these https://nl.mouser.com/ProductDetail/...r983RJeg%3D%3D, but now I'm wondering if they are the correct ones. Unlike the usual case where they are placed before the bridge rectifier, these are placed next to each of the two main capacitors. I plugged the PSU in the current limiter and turned on the current limiter switch. Nothing blew! The light bulb was dim. I checked the voltage on the main capacitors and it read about 200V. Then I decided to attach the fan, and after turning on, I saw sparks and smoke somewhere in the area of the main capacitors (top left corner in the picture), but I couldn't tell which component got burned! After that, the light bulb was full on...I'm not sure if the fan caused the issue or it was just a coincidence. Also, I would expect some short, but measuring the resistance between the AC leads show something like 200k Ohm, so now I'm not sure what is wrong. I checked all diodes on the main side and they all seem to give correct values. The bridge rectifier also does not seem to be bad. Does anyone have any tips? The only thing I can think of now is to start removing components and measure them off circuit. As a last resort I'm thinking of buying one that is working and cross reference the circuits.
I uploaded an image of the PSU. I annotated the TRIAC with green, the bridge rectifier with red, the MOVs with blue. Also note: I found solder on windings of the component in yellow (is this a transformer?). Not sure if that came from me, but I was able to remove most of it with a solder wick. Not sure if this could be a potential issue.
