Ya got the rest of my transistors the other day and then realized DigiKey missed 2 of the MJ15004, so they are coming today. Keep my fingers crossed. So far all has very close hfe.
Well good news..got the right channel completed with +50 and -50v supply connected and input shorted I have about 20mv. Hopefully when connected to the input board that will lower more. Must of had some transistors leaking under full power even though no shorts were indicated.
We will see how left channel goes. Yes very hard amp to work on.
We will see how left channel goes. Yes very hard amp to work on.
What kind of meter were you using to test those old transistors?
I use an old Fluke, I think a 77 with diode test, has never failed me, I find them 99.9% of the time.
I use an old Fluke, I think a 77 with diode test, has never failed me, I find them 99.9% of the time.
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I'm using an old Heathkit IT-3120 but I cross-check with a Peak Atlas DCA-75...I actually like the Heathkit more for this particular testing/matching.
I would throw that out and learn to use the fluke, diode test.
I have one of those and they are slow and unreliable for in circuit tests.
Use the Heathkit to match new parts only
I have one of those and they are slow and unreliable for in circuit tests.
Use the Heathkit to match new parts only
Oh, I have a fluke but I'm not doing in-circuit testing, plus the fluke is more of a go/no-go test, right? BTW, I do use a Hy-Tronix Model 900 for go/no-go in-circuit testing but it's similar to the diode check method using the fluke....
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Update...I finished replacing transistors in left channel powered it up and 28mv offset. Must of had some leaky ones in there also.
Now the bad news....I remounted the preamp board and resoldered all power and input connections. I only fired up left channel. As soon as I applied power the new AM2 board had 2 resistors and one or 2 of the MJ340/350 caught fire and burned up!!! I had put power to these a few weeks back when I noticed I still had high DC offsets. I haven't had a chance to see what made it burn up. I may check voltages first to make sure 15 volts is still ok before power up the right side. Bit of a bummer as I felt I was finally getting there and many hours working on this thing.
Now the bad news....I remounted the preamp board and resoldered all power and input connections. I only fired up left channel. As soon as I applied power the new AM2 board had 2 resistors and one or 2 of the MJ340/350 caught fire and burned up!!! I had put power to these a few weeks back when I noticed I still had high DC offsets. I haven't had a chance to see what made it burn up. I may check voltages first to make sure 15 volts is still ok before power up the right side. Bit of a bummer as I felt I was finally getting there and many hours working on this thing.
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I had 50 volt fuses out and checked the +75 and -75 supply..all ok. The +55 and -55 and +15 and -15 are also ok.
So put in fuses on the right channel 50v supply and brought it up slowly on variac, no issues up to 50 volts the AM2 board is ok, but at full voltage now with the preamp board connected I am getting 6 volts on the right channel speaker output. I had about 25mv with the power section only and input shorted.
So put in fuses on the right channel 50v supply and brought it up slowly on variac, no issues up to 50 volts the AM2 board is ok, but at full voltage now with the preamp board connected I am getting 6 volts on the right channel speaker output. I had about 25mv with the power section only and input shorted.
They were both mounted correctly. The 350 to tab side and the 340 not to the tab side. The right channel board did not blow up and was built the same. I haven't tried a signal on the right channel from my sig generator as I now have 6 volts dc offset as I stated above. My AM1 and AM2 original board were ok, I built these new ones as I was told they were causing my offset, but in fact it was transistors in both outputs causing this.
Thanks, Ya the 340 transistors have to go the other way as per the designer. Something on the board went shorted...weird other channel ok.
I have to figure out what happened to the 2 burnt resistors in the left channel AM-2 module. In the mean time, right channel is ok, but as I mentioned from 25mv offset to 4 volts when I connect the preamp module. I think I will unsolder the orange wire going to pos terminal from preamp board, looks like a feedback going al the way to U2 U1, and a few diodes etc, maybe so DC getting through, Going to see if the 4 volts is coming from there.
I removed the orange feedback wire and it made no difference. With the blue input wire going to the power module disconnected now , I have almost no DC on the output on the right channel. On the new AM2 module I built we have 27vdc on U1 and 17v on U2 which feeds the output to the power module.
Something now in the predriver section is causing the 6v on the output. I still have to deal with the burnt out AM2 on the left channel.
Deafbykhorns any idea what is causing them. Voltages to modules all ok. With input shorted not sure I should be seeing 27 volts going into the AM2 module.
Something now in the predriver section is causing the 6v on the output. I still have to deal with the burnt out AM2 on the left channel.
Deafbykhorns any idea what is causing them. Voltages to modules all ok. With input shorted not sure I should be seeing 27 volts going into the AM2 module.
I told you earlier in the thread you had these installed wrong but you ignored it.
To be honest, you would of been better off letting someone with more experience do the troubleshooting.
Its really not that difficult to troubleshoot and repair these amps. I would start a new thread if you want help from others as this thread is getting a bit derailed. Stick with tubes...
To be honest, you would of been better off letting someone with more experience do the troubleshooting.
Its really not that difficult to troubleshoot and repair these amps. I would start a new thread if you want help from others as this thread is getting a bit derailed. Stick with tubes...
What was installed wrong the 340 and 350 transistors? The 350 were on the trace side and the 340 were flipped the other way. The right side board was built the same and did not blow up. Ya I have had enough of this thing and throwing $$$ at it. Should of never bought something that had over 130VAC hit it.
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Can you provide a couple of pics of the AM1/2 boards you built? The top down view you previously posted makes it very hard to judge the 340/350 transistor orientations.
I know this is kinda late advice, but it's a good practice to always use a dim bulb setup to prevent massive current surges if there's a short, and also to bring the equipment power up slowly on a variac for initial start ups...That said, you're almost there, just test the AM1/2 board components and replace the ones that are bad/questionable...
Here have a look. The left channel that took the AM2 board out, I also found a bad 6.2v zener CR11, I think there maybe other issues as in circuit some of the diodes touching that zener are measuring bad but, removing one it's ok, therefore something else is not right, again, probably why AM2 burned up.
Also Deafby I appreciate sending the files and bom to build the 4 modules, but I have over 40 years experience in this stuff, I actually have a college degree in electronics, but never went in the field as back in 1976, fixing tv's didn't pay very well and I got into a similar field making 3x the money. So I do have experience, but never worked on a 100 watt amp like this other than a few Haflers. So it wasn't very polite to say should of found someone with more experienced to fix this. I hope this isn't getting like facebook where everybody back stabs everyone. This should be a hobby where we enjoy what we are doing and people with more experience give comments and things to try. I won't bother you any more.
Also Deafby I appreciate sending the files and bom to build the 4 modules, but I have over 40 years experience in this stuff, I actually have a college degree in electronics, but never went in the field as back in 1976, fixing tv's didn't pay very well and I got into a similar field making 3x the money. So I do have experience, but never worked on a 100 watt amp like this other than a few Haflers. So it wasn't very polite to say should of found someone with more experienced to fix this. I hope this isn't getting like facebook where everybody back stabs everyone. This should be a hobby where we enjoy what we are doing and people with more experience give comments and things to try. I won't bother you any more.
