ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I have almost finished servicing this wonderful turntable, and only 1 annoying problem remains.
It does not "see" if the LP/or single disk is actually present on the plate. Happily lowers the needle on the metal! Good I had a plastic cover on and managed to capture.
Careful testing shows that I do get good signal from the black ribs all the way to the pin 9 on P6 connector. Tweaking with R64(was not existing in my model) did not produce any results. I get a see-saw pattern on oscilloscope at 13.3Hz with tops at 3.56V (max 4V with tweaking with R64) and min at 60mV.
What might be wrong?
Thanks in advance for any tips!
the tonarm moves to the start of the platter, and puts down the needle on the bare metal precisely where LP record should begin. If I have a single (45) on the platter, same thing happens - the needle ends up on the metal where the LP record should have been.
Taras, you have email.
Martin
Thanks for your advice, Martin
I did exactly as you recommended.
The signal is present on the pin of microprocessor (pin 33).
The height of sensing tonarm is adjusted to 19.5mm. I can see a focused light on the turntable.
The electrical signal is a nice see-saw pattern with 4V tops and 0 minimum all the way to pin 33 on chip.
Nothing changed in behaviour though. I think my IC is damaged.
All options exhausted, I guess. :-(
Let me know if anyone has access to working microprocessor, please.
Check the signal from the opto(s) at the end of the threaded shaft for the carriage.If no pulses are registrered when the carriage moves toward the record (and beyond), the drow-down count will never be reached and thecarriage will just continue to the center (and stay there until you press stop).
In other words, it will never get to the point where the CPU starts looking for a record.
Thanks, Martin!
I checked. This part works fine. The signals are present, and carriage moves to the point where the rotating disc starts and the needle drops on the record, if it is present, in the right place. It plays LP records just fine. Problem is when there is NO record present. Then the needle is still dropped on the metal disc, where the record should be. Very bad for the element... Same thing repeats when there is single (small 45 rpm) record is on the turntable.
Oh, so the problem is not, that it doesn't see the record (as the title suggests) but that it doesn't see when there's NOT a record.
Check the lamp in the sensorarm.Check its placement in relation to the lens system.Check the sensorarm height (even a mm can set it off)Check that the light from the sensorarm forms a reasonably correct and defined circle on a record.With no record on the platter, let the sensorarm hover above the rotating platter, reading the radial streaks and see where the signal fromthe sensor gets lost. A broken sensor wouldn't be a first. As would cracked solder joints at the boards edge connectors and where the ribbon cablefrom the processor housing is soldered to the main board.