Replaced Q12 with a resistor of same value. Now have 42v and 40v across each channels plate resistors. But of course the transport has decided to not read, LOL. So now I need to install the new transport to test the output.
Is it not reading an CD, or the test CD? I once cleaned the top loader CD player from my mother in law with a bit of ethanol. I knew the trick from tapes, and thought, why not, if it breaks it is just a bose anyway. It played everything, also CDrs, again 🙂
I know its not to be done but wonder if pulling all the tubes on the right side of the Plate the voltage will show 150vdc or a little more. If not then go back to the power supply where both 150 V comes from.
Also since both of the Plate voltages come off of Q1 if the voltages at R15 and R17 before and after the 160 ohm resistors read the same. Also wonder if those filter caps are still good from C30-C33.
Also since both of the Plate voltages come off of Q1 if the voltages at R15 and R17 before and after the 160 ohm resistors read the same. Also wonder if those filter caps are still good from C30-C33.
Tried cleaning it good. This was and is the primary issue with these units. I have a spare transport just need to install it
Well . . . New transport is in. With a resistor in place of Q12, still have low output on the left channel (which was thought to be good). I think this unit had multiple issues. The low channel could be not even related to the plate voltage problem, or maybe it is. But now with the resistors I have about the same voltage across the plate resistors but now low output on that left channel.
How much is low, in comparison to the right channel? Like half?
I am looking forward to your measurements of AC at the grids and plates of the triode. If the signal is coming in well on both channels, we will find out what the problem is. If there is a weaker signal coming in (at the grid) of the left channel, then it is in the DAC (no schematic for that)?.
Just saw that there is a relay RL2 in the left channel. I do not know what the function is, but if one channel has this closed, and the other not, it will probably give a different signal level at the grids.
I am looking forward to your measurements of AC at the grids and plates of the triode. If the signal is coming in well on both channels, we will find out what the problem is. If there is a weaker signal coming in (at the grid) of the left channel, then it is in the DAC (no schematic for that)?.
Just saw that there is a relay RL2 in the left channel. I do not know what the function is, but if one channel has this closed, and the other not, it will probably give a different signal level at the grids.
If you notice that RL2 is actually the same relay on both channels, its an internal gain switch. There is a jumper on the board labeled gain. I'll try moving it just to see. So in looking for the signal voltage, I'm after AC on the grid pins or AC on grids and plates?
Thanks regarding RL2. It could be that one contact is still working, the other not.
Please measure at both grid pins and plates. If we get weird measurements (probably we will) you can also take out all the tubes and measure again at the grids, to make sure the signal is present well at the grids. But first please with the tubes in place.
Please measure at both grid pins and plates. If we get weird measurements (probably we will) you can also take out all the tubes and measure again at the grids, to make sure the signal is present well at the grids. But first please with the tubes in place.
When measuring the grid on AC, what pins am I doing? Since its AC I dont want one probe on grid and one on ground or do I? Sorry if this is a stupid question. just trying to get it right.
You do indeed put the black probe on the audio ground (let's say the RCA shell), or any other easily available audio gnd (not to confound with the chassis ground). Leave it there, now with the red probe you poke around the pins for the grid and the plate. When playing the test CD, the sine will be amplified throughout the circuit, and you can measure with AC setting.
Of course it won't read the cdr. But even just a music cd is enough to get an idea. This makes no sense. On grid 1 the low output (left) side has about a volt higher ac than the normal (right) output side. Also the output on the rca is higher on the low output side than the normal side. This makes no sense to me.
With an audio CD it is indeed hard to take any good information regarding output levels. Do you have the option to get a non CDR test CD?
Yeah I'll have to order something factory. I had that cool digital domain test cd somewhere. Although even with music if wasn't varying too much. Easy to see that left side actually had more voltage than the right. It may be time to call it quits ans list on the audio sites. Get my transport and tube money back and be done. The DC side seemed easier to track down. Not sure I have it in me to track down the AC side.
But again, thank you very much for all your time. I really do appreciate the help on the DC side of things.
But again, thank you very much for all your time. I really do appreciate the help on the DC side of things.
Now that DC is stable, AC is probably even easier, as you do not have to run to shut down the player, but can let it run as long as you want, but without a decent signal it is indeed hard, or impossible (in audio testing one uses a signal generator, in your case it would be the disc). Did you measure with two DVMs to define that one output is higher than the other? You may just have measured a plucking string on one channel, and 2s later some silence on the other channel.
@Jimmp11, with everything you have done you may be very close to solving this. It would be nice to see on a copy of the schematics all the voltages at all point of that circuit and we could see exactly what is going on and what is not jiving on the circuit. You have one good channel and should use that as a reference. The Plates share the same PS line so going from there forward in the circuit should help and narrow it down, it will just take time but will be worth it once its found.
Background on this unit, was it ever serviced or messed with before you got it? If so, what had been done to it that you may know of. I have to go back and read all these pages of what you have done to it or if you can list everything you have changed out so far would be a great help. I just got this gut feeling you are close since you replaced the power supply caps already and the voltage are good on one side. I would hate to see you go through all this time troubleshooting and it finally be something simple and you had already sold the unit. It's a great sounding CD player and I know I have heard it. Sometimes if we just step back for a day or two or a week and not be in a rush then come back to work on it, something may just pop out that we missed or overlooked. This has happed to me at work and at home doing repairs.
Hang in there, we are closing in on what is wrong.
Background on this unit, was it ever serviced or messed with before you got it? If so, what had been done to it that you may know of. I have to go back and read all these pages of what you have done to it or if you can list everything you have changed out so far would be a great help. I just got this gut feeling you are close since you replaced the power supply caps already and the voltage are good on one side. I would hate to see you go through all this time troubleshooting and it finally be something simple and you had already sold the unit. It's a great sounding CD player and I know I have heard it. Sometimes if we just step back for a day or two or a week and not be in a rush then come back to work on it, something may just pop out that we missed or overlooked. This has happed to me at work and at home doing repairs.
Hang in there, we are closing in on what is wrong.
Well, so I do not think anyone messed with it. I guess the new troubling thing that I think I'm done is this new transport - Same issue. Sometimes it reads and sometimes it does not. That is really bad! The transport was sealed brand new. So now we have transport issues still, we have unequal output, we have the DC voltage - Which the resistor may have solved (thank you). But with the transport still not reading I think I'm done. You can open and close it 10 times and it may read all 10 or none. I mean it could even be bad voltage to the transport at this point. Just too many issues.
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