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Post by prime on Aug 19, 2023 21:42:17 GMT
I replaced both Q11and Q12 with brand new transistors TIP41C-1 and TIP42c-1 ,connected board, set multimeter on DC voltage i get -34 on base, i get -34 on emitter and +34 on collector on Q11, i dont thing think the new transistors are bad, they are all reading the same. From what i read i should be getting only 1volt coming to the base but im getting -34 I also tested Q12 I get -34 b -34 c -34 e
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Post by prime on Aug 19, 2023 22:14:36 GMT
FYI, both boards are identical readings except for a few volts, both channels give the same readings with the boards.
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Post by jukenorman on Aug 20, 2023 9:50:00 GMT
Oh, so you're getting negative voltages there and not positive voltages which makes a world of difference! But it's still quite hard to see how the negative voltage might be getting there. As for it being the same on both channels, all that is required is for the same mistake to be repeated on both boards.
I think we've reached the end of the line here, you're going to have to seek help from somebody competent, send it out somewhere maybe?
Norman.
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jski
New Member
Posts: 18
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Post by jski on Oct 4, 2023 3:05:40 GMT
I had the same problem but my fix was easy, i cleaned the prongs on the volume control plug in and worked like new,,,,,,  |
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Post by prime on Oct 24, 2023 17:41:53 GMT
Hi Norman and gang, I know the last answer was to get an expert, I sent out amp but to no avail, I picked up another used amp, I realize there is no guarantee it was working , but i tried it in the box and got the same response as the amp i was working on, a very loud high pitched hum . Im thinking it may be a power supply issue or speaker related problem. I tested the power coming from the amp power supply and found going from the top of the 12 pins, top row all VAC left connector 23.6 v center 8 right 23.6 next row 0 next row 0 last row left 0 center 0 right 26v . also i checked resistance at speaker plug left side .6 ohm right side .6 ohm. Just wondering if all seems normal. pete
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Post by jukenorman on Oct 25, 2023 13:41:26 GMT
What exactly was the verdict on the amp that you sent out? Off the top of my head, isn't it only centre tapped AC that goes into the amp from the power supply - your 23.6 - 0 - 23.6 that you measured maybe? Aren't the rectifiers etc for the amp DC within the amplifier? While not totally ruling it out, I think it's less likely that it would be a power supply issue. I think though that the audio distribution assy, which comes between amplifier and speakers could well be an issue. I haven't read back through the thread but there's one thing that definitely bears repeating - you really need the schematics!
Norman.
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Post by prime on Oct 26, 2023 14:00:34 GMT
Hi Norman , i think i have narrowed down the problem, just not sure of the solution, on both amps i cannot get the right channel board to adjust properly, R25 calls for 0 to plus or minus .001 volts. On right board i can get it no lower than 2.1 no matter what i do , on the left board i can get it to 0 volts ,then i can set R33 to .003. It plays fine. Because i cant get the right R25 down to 0, i cannot adjust R33 so i get a loud hum if i try to use it. It happens on both amps so its either an issue with the connector or power supply. Any thoughts on this pete PS left channel stopped working again and will not adjust, just shows over limit on millivolt. Im starting to think transformer. I looked at the power supply and i see i get the power from the transformer, with no components in between. Ive looked at all of the schematics in the manual but it does not show from power supply to amp so i cant follow the feeds.
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Post by prime on Oct 26, 2023 21:29:23 GMT
OK i was able to get the left going but then the right wouldnt adjust, i left it for a while and the right adjusted but now the left stopped working and caused a loud hum, i removed both boards and again found all readings similar. I reinstalled both boards and adjusted the right ,then left, they both adjusted, tried sound and both channels work. Going to try again in the morning but i will not be surprised if it doesnt work. Its strange that i have had almost identical issues with two seperate amps. Unfortunately this amp has not been fully recapped. I may just leave it if it still works in the morning.
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Post by jukenorman on Oct 27, 2023 9:50:11 GMT
Pete, there is one thing that I have said many times (probably even in this thread) about these particular amplifiers - the inter-connects are extremely iffy! Rather than fiddling with the bias on your replacement amp (which there should have no need to do!), you would have been better looking at the circuit board connectors - suck off the solder and re-do it especially the male connectors. These intermittent type problems just scream bad connectors!
Norman.
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Post by prime on Oct 27, 2023 11:45:11 GMT
I agree i should not have needed to re adjust the bias, unfortunately i could not even turn on the amp until they were re adjusted. As far as solder goes, earlier in the post on my first amp i stated i had reflowed all of the solder on all boards, it was recommended by Ron in one of my correspondence to him. It has been made quite clear in the posts that the Rock-ola boards have this issue. The second amp i tried had been listed as working , i do realize that could be misleading info but the amp acted exactly as my first amp. I will definitely redo all of the solder joint on this amp . But if this issue returns not sure what i will do if anything. Thankyou as always for your time and help, it is greatly appreciated. pete
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Post by jukenorman on Oct 27, 2023 14:15:59 GMT
To be clear, I'm not talking about reflowing solder on the boards but the connectors, particularly the ones the driver boards plug into (referred to in the parts list as post connectors). I can't remember the exact construction of the amp, are they on some sort of motherboard?
Norman.
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Post by prime on Oct 27, 2023 18:51:28 GMT
Yes Norman i know which ones i think, i did all of the ones with posts sticking out for connectors and while i was at it all components to assure it was not a contact issue. The amp i bought for replacement is working so i will leave it, just for curiosity i reinstalled the original amp but still could not get R25 below 2.0. After which it would climb up again either way of turning the trimmer.
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