I'm just a hack hobyist with enough knowledge to be dangerous. I think I do know of a digital scope I coud borrow.
Digital scope would certainly be easier, but you can see what you need to see in a dark room (and adjusted beam intensity):
Been ages since I've powered on this 2245.
Been ages since I've powered on this 2245.
The litmus test for a PLL direct drive is the drive waveforms - if there's anything going on, you'll see it there.
This is what a typical well-running MKII drive looks like:
And here's one with issues:
These are two different motors but the same drive/control. The issue with the second one is that the motor had too many windings on the phase on C1. Only ran in to that issue once.
For reference, this what the drive looks like when it's ran open-loop:
This is what a typical well-running MKII drive looks like:
And here's one with issues:
These are two different motors but the same drive/control. The issue with the second one is that the motor had too many windings on the phase on C1. Only ran in to that issue once.
For reference, this what the drive looks like when it's ran open-loop:
Here's what I was able to capture using the old scope & a DSLR.
The spikes look bigger than the ones in your examples if it indicates anything.
The spikes look bigger than the ones in your examples if it indicates anything.
According to the scope, it's 100 but I don't know how accurate it is.
Since I've stared scoping it, stepping through speeds, tapping on platter, etc. it's running rougher and the vibration isn't so subtle. I haven't checked any of the settings to see if they're now off.
Since I've stared scoping it, stepping through speeds, tapping on platter, etc. it's running rougher and the vibration isn't so subtle. I haven't checked any of the settings to see if they're now off.
I went back, shot another photo & paid closer attention. I also checked my scope with a signal generator & learned that I was reading the scope wrong - the grid are the divisions, not the little ticks. The time looks pretty accurate. I also went back and reset the sync positions because I had them set wrong & re-checked the oscillator. To the best of my ability it seems like its running at about 277.7 kHz if it makes a difference.
This is 100 ms/div and 2V/div, probe set at 1x. The period looks like 1.7 div = 0.17s => 5.88 Hz, which is in the ballpark?
This is 100 ms/div and 2V/div, probe set at 1x. The period looks like 1.7 div = 0.17s => 5.88 Hz, which is in the ballpark?
33.3RPM is 5.55Hz drive. No ballpark, but that's not what I'm looking for - it's the overall shape of the drive waveform. Your is indicative of an issue - the motor is difficult to turn, it's fighting itself due to offset voltage being incorrect, etc. I recommend 10X probe as the 1X will load the circuit. Sometimes the doesn't matter, but if you're not able to make that determination you're better off just sticking with 10X.
If you haven't gone through the motor, perhaps do that. It'd have to be pretty bad to cause this, but I've seen several that had worn through the thrust pad. You can also try backing off offset voltage, if even for a little while.
I'm heading out of town for a week so won't be much help during that time.
If you haven't gone through the motor, perhaps do that. It'd have to be pretty bad to cause this, but I've seen several that had worn through the thrust pad. You can also try backing off offset voltage, if even for a little while.
I'm heading out of town for a week so won't be much help during that time.
I'll use 10x from now on as I continue to learn & look at the motor & offset voltage. Thanks!
The DC resistance of the FG coil (CN2 9-10) is 362 ohms if that has any significance.
Picking up digital scope this weekend so will hopefully be able to get a clearer view of what's going on. I'm going to start re-capping and replace pot VR201 that controls RS current which I can't get very close to 0.
The DC resistance of the FG coil (CN2 9-10) is 362 ohms if that has any significance.
Picking up digital scope this weekend so will hopefully be able to get a clearer view of what's going on. I'm going to start re-capping and replace pot VR201 that controls RS current which I can't get very close to 0.
Does this look a little better?
I finally followed your instructions, and backed off on the offset voltage which resulted in this. Sorry for not doig it sooner.
Adjusting the offset voltage while watching the motor waveform was very revealing. There is a clear point where it gets very erratic.
After doing this I went back to VR201 and was able to adjust it to get the RS current setting to 0V. I then went back to set sync positions.
I do think I still feel a very subtle vibration so I'll look at the motor. Is this waveform still concerning in your opinion?
Thanks again for your patience
I finally followed your instructions, and backed off on the offset voltage which resulted in this. Sorry for not doig it sooner.
Adjusting the offset voltage while watching the motor waveform was very revealing. There is a clear point where it gets very erratic.
After doing this I went back to VR201 and was able to adjust it to get the RS current setting to 0V. I then went back to set sync positions.
I do think I still feel a very subtle vibration so I'll look at the motor. Is this waveform still concerning in your opinion?
Thanks again for your patience
Well done ! JP has worked with me in the past and is familiar with the 2A. To me the waveform looks OK but there should be absolutely no vibration at all, none at all.
You probably need to find a position of VR201 where it remains in lock at all speeds at all temperatures. I got caught out with this on my own MK3
You probably need to find a position of VR201 where it remains in lock at all speeds at all temperatures. I got caught out with this on my own MK3
Juist a sanity check: is there vibration with the platter on or with it removed? With the platter removed, there will be vibration.
After my last post I realized that if I start it at 33, it now won't lock but if I jump from 33 to 45 or 78 it locks at the higher speed. Once locked at 45 or 78 I can then press 33 and it will slow down & lock at 33. VR201 is currently set to the factory service manual spec of 0V but now I realize that the service manual isn't always right after my experience with offset voltage.
The platter is on. I ran it some more this morning & now I think there is no vibration.
IIRC the rest of the SM settings for the MK2A are correct. There is a service bulletin update for that table, though. I've one on the way.
Motor waveforms look okay. A bit less "peaky" would be nice, but there's a lot of variability between samples and I have to remind myself that this units hasn't been refurbished yet. The example I posted above was an NOS motor fresh from a clean and lube - not many are going to be that good.
Here's a quick and dirty video on setting offset voltage. Forgive whatever crud I'm getting over - I don't normally sound like a seventy-year-old chain-smoker.
Time to pack.
Motor waveforms look okay. A bit less "peaky" would be nice, but there's a lot of variability between samples and I have to remind myself that this units hasn't been refurbished yet. The example I posted above was an NOS motor fresh from a clean and lube - not many are going to be that good.
Here's a quick and dirty video on setting offset voltage. Forgive whatever crud I'm getting over - I don't normally sound like a seventy-year-old chain-smoker.
Time to pack.
Make sure offset is backed off too far and double-check sync position. Those aren't critical - about 40/60 and you're good enough.
**EDIT ISN'T backed-off too far!
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