I will report back when it comes in-house. I was down at the friends today for something else and just had a quick look at it. There is 80VDC on the rails is and (I think) thats about right. There is 90VDC on the outputs of left channel. I'm wondering where has the additional 10v has come from (as well as the 80vdc itself).
The open ground is a definite possibility. Thank you everyone for all your input. I posted here before I even have it on the bench so that the replies can be mulled over before I start to work on it. The friend is afraid of the amp now and want to sell it after I get it going for him (and of course has lost a level of faith in me, but I dont think it is my original work, something else has probably failed but who knows.) I considered doing all the outputs the first time round but I was trying to keep costs down...and..they tested OK. Will keep you all posted. May be a week or longer before I get it on the bench. Thanks!!
BL
The open ground is a definite possibility. Thank you everyone for all your input. I posted here before I even have it on the bench so that the replies can be mulled over before I start to work on it. The friend is afraid of the amp now and want to sell it after I get it going for him (and of course has lost a level of faith in me, but I dont think it is my original work, something else has probably failed but who knows.) I considered doing all the outputs the first time round but I was trying to keep costs down...and..they tested OK. Will keep you all posted. May be a week or longer before I get it on the bench. Thanks!!
BL
All I had was a DVM (the friends) and connected to the left output binding posts. When on: 90VDC. Didnt note the polarity and wish I had. It was the negative rail fuse that was blown (and its replacement was "ready to blow" - the center of the filament was charred but it did conduct as we measured seprately to make sure) When off: Outputs not open or shorted. Essentially the same resistance as the good channel (didnt note it - the fact it was the same made me think the output x-istors are ok. The other channel does work. Sound came out of it.
BL
BL
Hi computeruser,
A power output transistor can be damaged and still measure open C-E or C-B. You need to be able to measure gain and leakage. Normal DVM's normally won't do here.
So a presort would be a diode test on a DVM to measure the B-E and B-C junctions. After the parts pass this test we want to see that the hFE (DC current gain) is within normal ranges. Anything too high or low gets binned. (garbage). A final test is to measure the C-B and C-E leakage. Any indication is a bad transistor. Heathkit made a great tester (IT-18, IT-121). A B&K 530 will give some info as will the Leader LTC-906. Of course a curve tracer will work but takes too long for service work. I use the Heathkit IT-18 most on the bench as it's perfect for this work. I have caught many transistors with the leakage tests. The odd new one too.
If you are going to do audio service, try to pick one of these up. If you can build one .... great, but check it first. The only other way to do reliable repairs is replace the outputs when you find bad drivers or a shorted output (generally a good idea in this case anyway).
-Chris
A power output transistor can be damaged and still measure open C-E or C-B. You need to be able to measure gain and leakage. Normal DVM's normally won't do here.
So a presort would be a diode test on a DVM to measure the B-E and B-C junctions. After the parts pass this test we want to see that the hFE (DC current gain) is within normal ranges. Anything too high or low gets binned. (garbage). A final test is to measure the C-B and C-E leakage. Any indication is a bad transistor. Heathkit made a great tester (IT-18, IT-121). A B&K 530 will give some info as will the Leader LTC-906. Of course a curve tracer will work but takes too long for service work. I use the Heathkit IT-18 most on the bench as it's perfect for this work. I have caught many transistors with the leakage tests. The odd new one too.
If you are going to do audio service, try to pick one of these up. If you can build one .... great, but check it first. The only other way to do reliable repairs is replace the outputs when you find bad drivers or a shorted output (generally a good idea in this case anyway).
-Chris
Hi computeruser,
You are going to love that piece of gear! I've got all those I listed and have had the IT-18 for about 20 yrs. That's the one that stays on the bench.
I have had to replace the leads (broke- worn out) and I made a plug in adapter for the Japanese transistors, this also works for TO-126 and 220 parts. I use a bigger socket for plastic TO-3 parts.
I use the gain test for a quick matching on power transistors and it's adequate for that. Just make sure you clean the battery contacts and use a fresh alkaline "D" cell. Some day I'll tear it apart and build an AC supply for it. I've been saying that for ten years at least.
The only thing I didn't get was the manual for this. Can't find it on the web in PDF either. Darn.
Take care, Chris
You are going to love that piece of gear! I've got all those I listed and have had the IT-18 for about 20 yrs. That's the one that stays on the bench.
I have had to replace the leads (broke- worn out) and I made a plug in adapter for the Japanese transistors, this also works for TO-126 and 220 parts. I use a bigger socket for plastic TO-3 parts.
I use the gain test for a quick matching on power transistors and it's adequate for that. Just make sure you clean the battery contacts and use a fresh alkaline "D" cell. Some day I'll tear it apart and build an AC supply for it. I've been saying that for ten years at least.
The only thing I didn't get was the manual for this. Can't find it on the web in PDF either. Darn.
Take care, Chris
I have the manual. One day ( no time...as always) I will scan
it and create a PDF. I , too, was looking for the PDF before I bought mine so I made sure the unit I got (from ebay) had one.
It is like new. I paid alot for it but that was the tester I wanted.
I also have a complete set of spares except for the meter movement. If there is a page or 2 that you need (schematic, calibration etc) let me know and I will scan that for you. The whole manual will take some time tho. The key to calibration is a resistor that comes with it. Mine fell out of the case when I got it and I thought it was a spare part that had been left inside when the person built it. It's needed for calibration, which is simple. The reason I wanted the IT-18 is that it can test in circuit. I have an IT-27 which works fine but the part tested must be out of circuit.
it and create a PDF. I , too, was looking for the PDF before I bought mine so I made sure the unit I got (from ebay) had one.
It is like new. I paid alot for it but that was the tester I wanted.
I also have a complete set of spares except for the meter movement. If there is a page or 2 that you need (schematic, calibration etc) let me know and I will scan that for you. The whole manual will take some time tho. The key to calibration is a resistor that comes with it. Mine fell out of the case when I got it and I thought it was a spare part that had been left inside when the person built it. It's needed for calibration, which is simple. The reason I wanted the IT-18 is that it can test in circuit. I have an IT-27 which works fine but the part tested must be out of circuit.
Hi computeruser,
I didn't get the calibration resistor. What value is it do you know? I can make up a none standard value easily, with precision, or use an RTD standard to "dial" it in.
If you could supply calibraton and schematic I'd be very grateful to you. Your offer is very kind indead.
I bought mine from the Heathkit store in Mississauga, Ontario when they were closing the store. It was built already and I didn't know about the cal resistor. I always wished I had the manual.
As for using the meter, I have always used it out of circuit. I don't trust in circuit readings from anything. I am not familiar with an IT-27. Guess I'm going to look it up on the web.
Thanks! -Chris
I didn't get the calibration resistor. What value is it do you know? I can make up a none standard value easily, with precision, or use an RTD standard to "dial" it in.
If you could supply calibraton and schematic I'd be very grateful to you. Your offer is very kind indead.
I bought mine from the Heathkit store in Mississauga, Ontario when they were closing the store. It was built already and I didn't know about the cal resistor. I always wished I had the manual.
As for using the meter, I have always used it out of circuit. I don't trust in circuit readings from anything. I am not familiar with an IT-27. Guess I'm going to look it up on the web.
Thanks! -Chris
Hi Barry,
Please email the info. The attachment may be too large to post. I do not have problems with file size.
Email is: bhome at sympatico dot ca . You should be able to find it in my profile as well.
Curious. How much did you get the IT-18 for? I think I paid $80.00 CDN for mine at the time (mid Seventies).
-Chris
Please email the info. The attachment may be too large to post. I do not have problems with file size.
Email is: bhome at sympatico dot ca . You should be able to find it in my profile as well.
Curious. How much did you get the IT-18 for? I think I paid $80.00 CDN for mine at the time (mid Seventies).
-Chris
Paid $73.00 USD for mine. I thought it was high compared to what others had recently sold for but "it was the one I wanted" so I just bid till I got it. It's like new, had the manual and had that resistor that fell out. It had been used but not much. The rubbers on the probe tips are still nice and not ripped. Nothing was corroded (posts, switches, battery holder). I'll scan the usefull stuff and e-mail it late tonight. You'll have the missing link.
My missing link is a schematic for a Sumo "The Power". The designer (James Bogniorno) will not give them out. He has helped me with everything else for it including lots of circuit updates. I did get it running but it must have taken me several hundred hours of work and was worth it.
Barry
My missing link is a schematic for a Sumo "The Power". The designer (James Bogniorno) will not give them out. He has helped me with everything else for it including lots of circuit updates. I did get it running but it must have taken me several hundred hours of work and was worth it.
Barry
Hi Barry,
Very kind of you and a big thanks!
I've repaired Sumo's before, got a schematic for one. All that stuff is with my old shop (sold). Most high end stuff I ended up tracing the schematic myself. Everything is a secret. Once you recognize the topology the rest falls into place, perhaps with a twist. Don't you wish these guys would just grow up? Anyway, you know know that amp pretty well. If I had it, I'd give it to you. I do have a few schematics and some Heatkit stuff if you need. No scanner so I take a picture with my camera. I do have some in electronic format as well.
As far as the price you paid, not too bad since it is complete. I think it's the best transistor tester ever made for service, and I know you'll get your money's worth out of it. So what is $80 marked up to today's dollars worth (oh, Canadian, so about $1.50 I guess
) All in all, a good deal I think.
-Chris
Very kind of you and a big thanks!
I've repaired Sumo's before, got a schematic for one. All that stuff is with my old shop (sold). Most high end stuff I ended up tracing the schematic myself. Everything is a secret. Once you recognize the topology the rest falls into place, perhaps with a twist. Don't you wish these guys would just grow up? Anyway, you know know that amp pretty well. If I had it, I'd give it to you. I do have a few schematics and some Heatkit stuff if you need. No scanner so I take a picture with my camera. I do have some in electronic format as well.
As far as the price you paid, not too bad since it is complete. I think it's the best transistor tester ever made for service, and I know you'll get your money's worth out of it. So what is $80 marked up to today's dollars worth (oh, Canadian, so about $1.50 I guess
) All in all, a good deal I think.-Chris
I've got schematics for pretty much everything else. I've acquired a whole bunch of test equipment in the last year and one criteria is I must have the full service manual so I can calibrate it. I even ended up with a Fluke 515A calibrator. Just to open some of the stuff up to see how it was built is worth the cost (example: HP 5245L Nixie tube counter) and you end up with (in every case - I've had no duds) stuff that is still so usefull, used to cost as much as a car, for often less than the cost of having it shipped.
Most of the time it just needs to be cleaned up.
Barry
Most of the time it just needs to be cleaned up.
Barry
Now thats interesting Barry. I used to work in a calibration lab. Also spent well over 20 yrs in audio service (and still am) and now work in telecommnications. It's unusual to find DIYers with a ton of test and measurement equipment.
I used a CD in the lab called DOD Midas. If you can find a copy, older is better for you, it has many calibration procedures and adjustment points for test insterments.
-Chris
I used a CD in the lab called DOD Midas. If you can find a copy, older is better for you, it has many calibration procedures and adjustment points for test insterments.
-Chris
I want one!!!! but thats going to be tough to find. I did a search and there is not much out there on it. I do have the cal procedures for everything I have. These often ended up costing more than the units themselves, especially the HP stuff, some of the manuals are the size of a telephone directory. I read your profile and one of your interests is "learning" which is one of mine. I have NO background in electronics and NO formal training. I learn as I go along. I havent lost many things so far to incompetance. This Adcom "may" be the first one. I still don't think it is simply because of how I work. When I first repaired it in January I ran it up to full power for a minute or longer as a stress test. Then ran it at 1/3 power (the old FTC conditions) for over an hour, then measured the distortion after the final bias adjustment. If something was waek that should have weeded it out. I really cant wait to find out what the heck happened.
Barry
Barry
Hi Barry,
I recall the lab manager saying these cost a lot via subscription. They destroyed the old ones as soon as a new one came out. Never could get a hold of one.
It sounds as though you tested it well. Unfortunately as leaky transistor can go after a while in service. Of course it may have been something else. Speaker wire being pulled out and shorting or not enough ventillation. These have a thermal shut off switch but running at high temperature isn't good for anything.
I have studied failures for years and I always want to know what went wrong. I feel for you in that respect. It's all a learning exercise.
-Chris
I recall the lab manager saying these cost a lot via subscription. They destroyed the old ones as soon as a new one came out. Never could get a hold of one.
It sounds as though you tested it well. Unfortunately as leaky transistor can go after a while in service. Of course it may have been something else. Speaker wire being pulled out and shorting or not enough ventillation. These have a thermal shut off switch but running at high temperature isn't good for anything.
I have studied failures for years and I always want to know what went wrong. I feel for you in that respect. It's all a learning exercise.
-Chris
Hi Barry,
Okay, so you are not drawing current. You have a DC offset (full negative minus a couple e-b drops). Since you found Q107 bad (good music - aaargh) have you checked Q106 and the resistors R112 & 113 for open? It looks like Q107 can't turn on. I would be surprised to see Q108 damaged as it's a ccs.
-Chris
Okay, so you are not drawing current. You have a DC offset (full negative minus a couple e-b drops). Since you found Q107 bad (good music - aaargh) have you checked Q106 and the resistors R112 & 113 for open? It looks like Q107 can't turn on. I would be surprised to see Q108 damaged as it's a ccs.
-Chris
Q105 was originally bad. Q107 - it took me a sec to get that joke.
I have been to Toronto. I started on the heatsinks. D301/C302
are good. Removed Q306 because I wanted to try the tester!!!
Beta is about 70. Iceo & Icbo dont even move the needle. I never even considered that it could be DC offset. Was approaching it as if the neg rail was leaking to ground (maybe the same thing?) Will now look in the area of Q105/6/7 - R112/3. May take a bit - have to remove the board.
I have been to Toronto. I started on the heatsinks. D301/C302
are good. Removed Q306 because I wanted to try the tester!!!
Beta is about 70. Iceo & Icbo dont even move the needle. I never even considered that it could be DC offset. Was approaching it as if the neg rail was leaking to ground (maybe the same thing?) Will now look in the area of Q105/6/7 - R112/3. May take a bit - have to remove the board.
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