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Hello folks,
I know keyboard stuff isn't typical on this forum, but I'm not really a member of the keyboard forums & frankly am too lazy to become one
.
So I guess this is a know common issue with these units and is attributed to on of the memory chips IC5, however it had already been replaced. So I replaced it anyway. BTW on this unit heating & cooling IC5 affected the issue, so it seemed a reasonable option to just replace the thing. The customer provided the 1R3R05, so I just replaced it. No change.
Since these IC's were salvaged from another unit by Syntaur, I decided to swap the IC with the one next to it to see if the issue changed and if heat/cool followed the IC I replaced.
The symptom did not move with the swap, so it had to do with the position, not the IC.
There is a resistor array that did not measure the same as it's next door neighbor, so I swapped them to no avail.
I did notice when I applied my meter to pin 4 (Labelled 'LIN' for Linear) of this memory chip, the symptom immediately stopped until I removed it. I could see that there was a voltage on the pin, but the meter seemed to shunt it out, so I knew it was a very high impedance.
SO, I began to trace where that went, as it was one of the few pins that the IC did not share with the other memory chips. When I touched the pin on a hybrid chip, the symptom did not stop as on the output of the resistor array RA-3 that connected to pin 4.
I determined that there was not continuity between pin 10 of the RA3 and the capacitor array (CA1) where it terminated, but there were no apparent bad solder connections or trace breaks.
See the attached pic to see what actually was going on. There must have been a microscopic copper track between that gap for all these years that finally gave up the ghost!
I jumped the gap with a very thin wire & Voila.
What a bitch! (but ultimately FUN for us weird types that enjoy this stuff
)
Thanx, Glen
I know keyboard stuff isn't typical on this forum, but I'm not really a member of the keyboard forums & frankly am too lazy to become one
.So I guess this is a know common issue with these units and is attributed to on of the memory chips IC5, however it had already been replaced. So I replaced it anyway. BTW on this unit heating & cooling IC5 affected the issue, so it seemed a reasonable option to just replace the thing. The customer provided the 1R3R05, so I just replaced it. No change.
Since these IC's were salvaged from another unit by Syntaur, I decided to swap the IC with the one next to it to see if the issue changed and if heat/cool followed the IC I replaced.
The symptom did not move with the swap, so it had to do with the position, not the IC.
There is a resistor array that did not measure the same as it's next door neighbor, so I swapped them to no avail.
I did notice when I applied my meter to pin 4 (Labelled 'LIN' for Linear) of this memory chip, the symptom immediately stopped until I removed it. I could see that there was a voltage on the pin, but the meter seemed to shunt it out, so I knew it was a very high impedance.
SO, I began to trace where that went, as it was one of the few pins that the IC did not share with the other memory chips. When I touched the pin on a hybrid chip, the symptom did not stop as on the output of the resistor array RA-3 that connected to pin 4.
I determined that there was not continuity between pin 10 of the RA3 and the capacitor array (CA1) where it terminated, but there were no apparent bad solder connections or trace breaks.
See the attached pic to see what actually was going on. There must have been a microscopic copper track between that gap for all these years that finally gave up the ghost!
I jumped the gap with a very thin wire & Voila.
What a bitch! (but ultimately FUN for us weird types that enjoy this stuff
)Thanx, Glen
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