Replacing a Solid State Rectifier

[Enzo]

Only if you are feeding it AC. A short across a cap can't hurt it.

[Perkinsman]

Ok, on another related issue...When I reattached the 2 red wires to the new rectifier, I reattached each one to the sine~ markings. Was that correct? When I looked back at the pics I took, it wasn’t that clear.

[g1]

I checked the new resistor & it’s still good but I’m the power supply board again, I found what I believe was the bad parts, a 1000uf cap & the F2 fuse. I replaced them, then tested the transistors & diodes, all good.... powered up, held for 30 seconds but then it sounded like the relay clicked & then another pop & smoke bomb!

What made you suspect them? That supply is unrelated to anything else you have done.
It did not blow fuse F2, before, but now it does after you replaced something. So you must suspect your work. (or maybe F2 was blown before and you missed it?) That is a low voltage supply for some of the indicator lights. What voltage capacitor did you use? Is diode D702 now shorted?

Ok, on another related issue...When I reattached the 2 red wires to the new rectifier, I reattached each one to the sine~ markings. Was that correct? When I looked back at the pics I took, it wasn’t that clear.

It depends if the 2 red wires are coming from the transformer. The schematic does not show this.

[Perkinsman]

What made you suspect them? That supply is unrelated to anything else you have done.
It did not blow fuse F2, before, but now it does after you replaced something. So you must suspect your work. (or maybe F2 was blown before and you missed it?) That is a low voltage supply for some of the indicator lights. What voltage capacitor did you use? Is diode D702 now shorted?


It depends if the 2 red wires are coming from the transformer. The schematic does not show this.

The 2 red wires are directly from the transformer to the big rectifier. The reason I suspected the cap and fuse were the problems was because I saw smoke from the power supply board and found the cap open then tested the fuses and found F2 bad. I used a 1000/63v, to replace the original 16v cap..and it still gets hot.

[Enzo]

OK, remove or disconnect the cap that gets hot. Put your meter probes to the points in the circuit that the cap connects to. Either points on a board, or loose wires, whatever. DC volts. WHich point shows positive and which negative. Then verify the cap was indeed connected to them that way. DArn few things make caps hot.

A common error is to install the negative cap backwards, thinking "the negative side always goes to ground, right?" Nope.

[Perkinsman]

I suppose it's possible the silkscreen is wrong but I thought I remember reading a thread here that stated Concept's boards were 100% accurate... I'll check tomorrow and update.

[nevetslab]

Prior to this latest issue with the 1000uF/63V caps, it looks like that 16A Bridge Rectifier that failed is associated with the 15,000uF/63V Buss Caps that provide the bipolar HV for the power amp circuits. The two pairs of NPN/PNP output xstrs look to be external to the rest of each circuit board....chassis mounted heat sinks. Have you checked to see if all eight of those power xstrs are ok, or have shorted parts? Those are usually what fail. Interesting to see on the negative collector side of each channel's output power xstrs....their collectors go thru a 4.7 ohm resistor to get to the negative supply rail, while the positive side xstrs go directly to the positive supply rail. You'll want to look at that resistor on each channel. You may find one of more open circuit.

[Perkinsman]

Prior to this latest issue with the 1000uF/63V caps, it looks like that 16A Bridge Rectifier that failed is associated with the 15,000uF/63V Buss Caps that provide the bipolar HV for the power amp circuits. The two pairs of NPN/PNP output xstrs look to be external to the rest of each circuit board....chassis mounted heat sinks. Have you checked to see if all eight of those power xstrs are ok, or have shorted parts? Those are usually what fail. Interesting to see on the negative collector side of each channel's output power xstrs....their collectors go thru a 4.7 ohm resistor to get to the negative supply rail, while the positive side xstrs go directly to the positive supply rail. You'll want to look at that resistor on each channel. You may find one of more open circuit.

Where did you find that was a 16A rectifier? The rectifier replacement I used was 8A, not 16A. I haven't checked any of the 8 transistors yet, do they need to be pulled off the heatsink to test? Do I test them with my DMM the same way I would any other transistor? I got sidetracked today but I'll check the polarity of the cap leads & those resistors tomorrow and update. Thank you.

[g1]

Where did you find that was a 16A rectifier? The rectifier replacement I used was 8A, not 16A..

The part number you linked that you said you ordered from Mouser was a 15A rectifier like the original. If you then changed the order to something else, you should not have chose a lower current part.

You guys are so good at what you do, I appreciate you! I spoke to the Mouser tech and put the order in earlier today but after reading your message, I just checked the datasheet, it's 29mm square but I told the tech 26mm, so they sent the wrong part: Mouser #12-GBPC1506.

Later you talked about 8A fuses.
What is the part number of the bridge rectifier you installed?

[nevetslab]

Where did you find that was a 16A rectifier? The rectifier replacement I used was 8A, not 16A. I haven't checked any of the 8 transistors yet, do they need to be pulled off the heatsink to test? Do I test them with my DMM the same way I would any other transistor? I got sidetracked today but I'll check the polarity of the cap leads & those resistors tomorrow and update. Thank you.

OH...my mistake....it was 15A/600V. The power xstrs can be tested for shorts (C-E, C-B, B-E) while mounted, though if the rest of the power amp circuitry is on removable PCB's, unplug them, so you're not also looking at the drive circuitry. yup....same way as any other xstr...mind the polarity

[Perkinsman]

My mistake too, the rectifier was 15A, Mouser# 512-GBPC1506. So today I removed the 1000/63uf cap that keeps getting hot, powered on and measured 1.6vdc and 23vac across the cap pads and checked the polarity, which is correctly printed on the board. I'm gonna test the power transistors tomorrow.

[The Dude]

If you have 23VAC and only 1.6VDC where the cap solders in, I'd say you have a rectifier issue before the cap. The cap should just smooth DC, it doesn't "make" it. Check C702 and D702.

[Perkinsman]

C702, D702 both test good. Pulled and tested the rectifier, 3 transistors and most caps on the power supply and all tested good, however F2 was open again. I tested all 8 power transistors and they were good BUT one was different than the rest, apparently it had been replaced at some time. It was labeled MJ15025G BM1608 MEX and replaced one of the 2SB655's. Is this the correct substitution, and if not, could it be causing C719 (1000/16 cap) to overheat and F2 to blow? Also, when a power transistor blows, should they be replaced in matching pairs?

[g1]

I'd suggest you replace D702 anyway. It could be failing when voltage is applied. The voltages you measured at the pads of C719 indicate either D702 is failing or C702 is shorted. You might want to try it with C702 removed as well. It does not need C702 to function.

[The Dude]

^^^^^^ Yes that. Something failing after the cap or attached to the supply would not likely blow the cap. Almost certainly the problem is D702 or C702.