I have a DMM. I also have a "pocket" style digital O scope. Haven't started using it though.
I'm not sure about "sharing electronics".
The tape head wires from each transport go to different parts of the circuit board, as can be seen in the photos.
I just connected a source to the L/R inputs and pressed record without a tape inserted. Both LED meters moved and I got audio from both L/R outputs, if that means anything.
I'm not sure about "sharing electronics".
The tape head wires from each transport go to different parts of the circuit board, as can be seen in the photos.
I just connected a source to the L/R inputs and pressed record without a tape inserted. Both LED meters moved and I got audio from both L/R outputs, if that means anything.
Well, every double cassette deck has only one set of inputs and one set of outputs, so the playback signals from each deck has to at one point become one
Cables from the heads go first to separate amplification and equalization stages to become line level signal
Do not waste your time looking for problem there
Signal then goes to big chips for dolby, if those are still separate, likelyhood that both right channel are wrong is low
At one point, there must be electronic, like output buffer, or output muting circuit, which is only one set for both mechanics, that's what i meant by 'sharing electronics'...problem is likely there
Maybe one channel is muted constantly
How about headphones output? Is there signal in right channel? If it has headphones jack, check that, that is certainly shared electronics
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If you have small scope, it can handle any voltages the decs present, I would walk backwards from the line out jacks and compare signals, ac and dc, side by side, the same components in left and right channel, while you play cassette. At one point you need to find spot that right channel has music signal, after than not. Good luck. It would be easier if you had schematics.
Unfortunately this does not help much, since dual deck typically do not have 'monitor' function, being two head type. In single deck with three heads that would be help. In dual deck playback part is unused during record.
Thanks. Yes it would be easier with a schematic. I'm working on this for a friend. I've fixed some electronics in the past that had obvious problems, but this one has me stumped. He doesn't want to spend any money on it and I can't find the schematics for free anywhere.
I saw a video recently where a guy was troubleshooting an audio circuit and his "tester" made a tone. It was like he was playing a tone on the deck and his tester was like a speaker and as he touched various points along the circuit path with his probe, he'd hear (or not hear in the case of a putting the probe on a faulty component) the tone. It seemed like a brilliant diagnostic tool for tracing audio circuits!
I saw a video recently where a guy was troubleshooting an audio circuit and his "tester" made a tone. It was like he was playing a tone on the deck and his tester was like a speaker and as he touched various points along the circuit path with his probe, he'd hear (or not hear in the case of a putting the probe on a faulty component) the tone. It seemed like a brilliant diagnostic tool for tracing audio circuits!
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Even without the schematics, its doable.
When you play cassette, audio ac signal can be detected with the scope. You put ground of the scope on ground of output jack and just touching the live to the component leg you will see if audio signal is present. You will see dancing ac line in the rhythm of music. That's the same as video you mentioned.
Well, the problem is likely where deck A right signal is merging with deck B right signal. Its located in the upper left part of the board.
You already tested line input and record, that is far right side of the board.
You can verify if both heads provide both left and right signal by testing ac in the middle left for deck A, nicely labeled there, just touch wiper of play level trimmer, left and right channel, repeat for deck B, all well labeled. Do not move the trimmer at this point, just check for music signal.
Once verified all is good there, what remains is small part of the board upper left. There may be some transistor which is not switched on or off and is not merging right signals. It could be just cold solder.
Good luck.
When you play cassette, audio ac signal can be detected with the scope. You put ground of the scope on ground of output jack and just touching the live to the component leg you will see if audio signal is present. You will see dancing ac line in the rhythm of music. That's the same as video you mentioned.
Well, the problem is likely where deck A right signal is merging with deck B right signal. Its located in the upper left part of the board.
You already tested line input and record, that is far right side of the board.
You can verify if both heads provide both left and right signal by testing ac in the middle left for deck A, nicely labeled there, just touch wiper of play level trimmer, left and right channel, repeat for deck B, all well labeled. Do not move the trimmer at this point, just check for music signal.
Once verified all is good there, what remains is small part of the board upper left. There may be some transistor which is not switched on or off and is not merging right signals. It could be just cold solder.
Good luck.
When you play cassette in the deck A, you can check signal on the playback level trimpots, PB level L, schould have music signal, as left channel is working, compare PB (playback) level R and see if signal is there, my bet it will be
You can do the same for deck B.
You can check the level on EQ trimpots, these adjust high frequencies, I would not move them, just check the level on wiper. If both channels have signal, your are ready to move to 'shared electronics'.
You can do the same for deck B.
You can check the level on EQ trimpots, these adjust high frequencies, I would not move them, just check the level on wiper. If both channels have signal, your are ready to move to 'shared electronics'.
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My bet the problem will likely be where both deck signals merge. But I am not certain what those chips are, likely some dual operational amplifiers. So I may be wrong here, but as I mentioned before, you can start from the back, from the line level out jacks and keep comparing left and right signal, till you find the problem.
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