I have an A810 which seems to be at a constant high speed. I have no PPL light. It flashes occasionally, but never syncs and stays on. I've removed the board and mounted it externally and extended the TAC and motor wires, so I can look at the signals on an O-Scope. It doesn't appear to have anything on the TAC lines. At first I was getting what looked like a decaying ringing, but when I turned off the machine and unplugged it was still there. I'm thinking I'm picking up spurious AC or signal from a ballast transformer. What should the signal look like at the TAC input of the Capstan Control Board?
Studer A810 No Capstan Control
- Thread starter kfalls
- Start date
It is possible but unlikely you have problem with the Capstan motor but seems you have issues with the Capstan Control Board.
I would suggest you look into Studer A810 service manual 3.4.6 Capstan Motor Control section for the proper signals you should get fro TP 1 - 8.
From my experience, one of the most likely situation that can cause what you have described might be from the bad L1 in Capstan Motor Control board. A810s with serial numbers older than 2xxx, it can have the center core supporting plastic material inside the inductor L1 (for that matter L3 as well) no longer supporting the ferrite core from the age changing inductance and resulting the correct 5.5Mhz measurement on TP1 you should get to be way off. Thus, PLL won't lock.
Ki
I would suggest you look into Studer A810 service manual 3.4.6 Capstan Motor Control section for the proper signals you should get fro TP 1 - 8.
From my experience, one of the most likely situation that can cause what you have described might be from the bad L1 in Capstan Motor Control board. A810s with serial numbers older than 2xxx, it can have the center core supporting plastic material inside the inductor L1 (for that matter L3 as well) no longer supporting the ferrite core from the age changing inductance and resulting the correct 5.5Mhz measurement on TP1 you should get to be way off. Thus, PLL won't lock.
Ki
I just fried my capstan controller on my UHA deck. You know how I did that ? I never knew it was a good idea to remove the sticky tail leader. I liked it for sticking to the supply reel for rewinds and keeping the tail firmly affixed to the supply reel when I was done listening. Apparently when I just let the reel just end without fast forwarding it...have done that for a few years for a consistent tape pack for storage...this one time, the sticky leader wrapped around the capstan and caused enough tape to wrap around it till it hit the pincher roller and stalled...literally burning out the capstan motor controller. Fortunately I did not lose music on the tape, as the tail was long. I have to ship my deck out for repair next week. Just a heads up for those who still keep their sticky leader attached to the tail end of the tape.
I had the same damn thing happen. Sticky tape wrapped around one of the rollers and capstan cut a groove into my $110 Athan pinch roller!!
Thanks for the quick response Ki. I see both L1 and L3 are 16uh, but L3 appears to be variable. I haven't been able to source these from the part numbers. Any idea where I can get them?
Both L1 and L3 are variable inductors. From my memory, if your machine is having issues with capstan PLL (no locking yellow LED on the panel), and have young enough Capstan Control Board with good L1 but have drifted beyond the spec (I think +/- 500Khz...), then you can adjust the ferrite core to get it within the spec to fix the problem. The risk is that if the L1 or L3 are too old and degraded, its ferrite core support will crumble and the board is useless... At times, the support plastic would shift the ferrite core in different position resulting in the signal out of spec for the PLL to work.
You would then adjust the L3 at TP 5 (I believe) for the maximum amplitude of the signal.
You can order both L1 and L3 from the Audiohouse (Daniella will help you) in Swiss. I did find a substitute part from Digikey with similar range of variable inductance but it had different pin-outs. It is better to get the inductors from the Audiohouse.
Last edited:
Good question, Tom. I shouldn't assume these things... sorry.
Yes, you can use any frequency counters with enough bandwidth to cover 5.5Mhz. However, I use a Tektronics TDS2012B (or C) two channel digital storage scope with measurement function that can be configured for amplitude and frequency measurements from the same screen for each channel and also do XY Lissajous plot for the head alignments. It works well and is very convenient - not to mention being small and light enough to sit on top of the VU meter housing on bigger machines such as A820 and A80s. I couldn't do that with the lug-able Sound Technology 1510A...
Last edited:
Similar threads
 | Steve Williams Site Founder | Site Owner | Administrator |  | Ron Resnick Site Co-Owner | Administrator |  | Julian (The Fixer) Website Build | Marketing Managersing |