Rowe AMI R-82 Memory Unit

TCW

Member
Joined
May 18, 2019
Messages
36
Reaction score
10
Location
Brownsburg, Indiana
I picked up non-working R-82.

This is my latest observation. These selections were made in secession one after the other after each record had been returned and magazine returned to home position. It seems to show a warmup of weak circuitry. Any information regarding component level repairs on any of the boards associated with the R-90 - R-93 class would be graciously appreciated.
Selection 101 picks up Slot 9 rather than Slot 1, next time Slot 6, then 2, & 2 again and then 1, & 1, & 1. that's got it! I then selected 102-106 and it picked them correctly in slots 2-6. Then I selected a B side, and I heard a click (B side solenoid) and the display stopped on the correct number (200), but the magazine continued to spin without end and the data LED had stopped flickering and was out. I cycled the power at the Scan Control Console and when it came to rest, I reset the Memory Unit. The data LED is lit, doing its flickering but now misses every record selected and will no longer pick up any records because it just keeps spinning. Sounds like something was not only warming up but failing and the Mech Control isn't receiving any signals to stop anywhere. I checked all the transistors and diodes in the Memory Unit. Maybe a weak cap or resistor changed value while being loaded? I would just replace all six of the fixed capacitors, but I imagine four of them would have an effect on the trimmer cap circuit that would alter the clock/data pulses (that's how it knows where to stop the Mech control).

I saw where member @omegaman set the frequency of the trimmer cap at 48 KHz on both the Memory Unit and Selector Logic unit. What I would like to know is at the Memory Unit are you supposed to measure the frequency right at chip Z704 Pin #7, Clock Send and (chassis as ground) also at Clock Send Pin#25 at Selector Logic chip Z501? Once I know where to read the frequency with my scope, I can see if that is my communication issue and I can replace the caps because they are old and i can recalibrate the frequency of the trimmer caps Memory Unit and Selector Logic unit.

Thanks for any help that can be offered to help in DIY repair.

Thanks, - Tom
 
Are you talking about the unit attached to the backbox or under the carousel? I do not use the unit attached to the backbox and it works fine.
 
This is the Memory Unit you can't play a record with out it. Its located under the Encoder. The Encoder is just below the turn table.mech electronics.jpg
 

Attachments

  • memory unit.jpg
    memory unit.jpg
    340.9 KB · Views: 2
Might be a connector issue. Have you tried cleaning the connectors?

One Rowe bubbler OMT CD player I worked on had a lot of bad transistors. I bought 13 new transistors and replaced them in the computer unit.

You might see if there is a service bulletin on this one, like there was on that one.
 
  • Like
Reactions: TCW
I re-soldered the headers all though that was done in the resent past.
I am not seen where to find the Service Bulletins for this era. The early AMI and anything from R-84 and on are readily available.
I did order 10 pairs of MPSA06 + MPSA56 as a refresh measure for this Memory Unit.
Regarding the connectors, the headers are bright but I will clean them with IPA to insure no film. Only the plug from the Mech Unit did I remove each wire connector and clean. This was due to being a loose a connection so I opened up the connectors a bit to apply more pressure to the header pin.
 
Still waiting on those transistors to arrive. And to think I made certain to buy from a US seller but there from Oregon with Free & Fast shipping but no tracking. Anyway, in the meanwhile I took the Credit Computer unit out. It has a pair of twin Sprague 35uf 50vdc electrolytic caps and both had black leakage on the + sides. As I was desoldering them the one was corraded clean through and the leg fell off.
1763193950438.png
I recapped what I had on hand for the power supply CR1009, the regulated -27 VDC it would hover around 15.5 VDC with no load but when the mech unit was operating it would run up to 26.35 VDC and as the mech came to rest about 60 seconds later it would fall back down to 15.5 VDC. This seemed like efficient use of power but a bit unusual for AC but considering it's a DC circuit with a DC motor I could see this as being normal. But with it being regulated it seems suspect to me. The cap was just out of spec so even though I had to parallel two 100 Mfd 100V caps I am hopeful for full operation.

1763192424019.png
 
Back
Top Bottom