My CDM1 Mk.II is finally fixed!, but now I have a question on the caps used

tonyptony · 19th February 2011, 01:15 PM

After living the last couple of years with disc initialization problems on my Proceed PDT3 transport I was fortunate enough to track down someone who had done a lot of work with these old Philips CDM mechanisms and had all the parts and test equipment to effect a repair.

In my case all that was necessary was the replacement of the caps on the servo board, and a realignment and refocusing of the swing arm and laser. I got it back and it works fine, but it doesn't seem to sound quite the same. Is it possible that replacing the servo caps could explain this? The originals were Nichicon VX types, which were replaced with Panasonic FM. I know that I shouldn't really make any judgements on sound until the devices are fully burned in, but right now I think I'm getting a slight bit of harshness. I did a bit of research and subsequently found that this is a characteristic of the FM caps, but would this be an audible effect from changing them in a servo circuit? If so I'm a bit worried. I was hoping to get my PDT3 repaired but sounding as great as it always did.

If this is due to these caps, is it something which will work itself out after device forming and burn in? Should I consider this an issue and look for which caps would be a better replacement?

Miniwatt · 19th February 2011, 02:04 PM

You have been listening to decades old caps that needed replacing: now you're listening to brand new ones. I'd wait until they have made a few hours

tonyptony · 19th February 2011, 02:30 PM

Quote:

Originally Posted by Miniwatt

You have been listening to decades old caps that needed replacing: now you're listening to brand new ones. I'd wait until they have made a few hours

Certainly good advice, of course.

I guess I was wondering if cap selection for a servo circuit could have as much of an impact as for signal carrying parts of a design.

JonHarrison · 19th February 2011, 10:14 PM

New caps could have ESR which is too low, do you have a scope to check the supply rails for oscillation ?

tonyptony · 19th February 2011, 10:50 PM

Jon, the main power supply rails? If so then yes, the fellow who did the work checked the rails afterwards on a scope. He did not indicate there were any problems. Maybe I should ask specifically about this.

JonHarrison · 19th February 2011, 10:57 PM

Yes, check the rails wherever the capacitors were replaced (with the unit playing).

19th February 2011, 01:15 PM	#1
tonyptony diyAudio Member Join Date: Mar 2006 Location: New Jersey	My CDM1 Mk.II is finally fixed!, but now I have a question on the caps used After living the last couple of years with disc initialization problems on my Proceed PDT3 transport I was fortunate enough to track down someone who had done a lot of work with these old Philips CDM mechanisms and had all the parts and test equipment to effect a repair. In my case all that was necessary was the replacement of the caps on the servo board, and a realignment and refocusing of the swing arm and laser. I got it back and it works fine, but it doesn't seem to sound quite the same. Is it possible that replacing the servo caps could explain this? The originals were Nichicon VX types, which were replaced with Panasonic FM. I know that I shouldn't really make any judgements on sound until the devices are fully burned in, but right now I think I'm getting a slight bit of harshness. I did a bit of research and subsequently found that this is a characteristic of the FM caps, but would this be an audible effect from changing them in a servo circuit? If so I'm a bit worried. I was hoping to get my PDT3 repaired but sounding as great as it always did. If this is due to these caps, is it something which will work itself out after device forming and burn in? Should I consider this an issue and look for which caps would be a better replacement?

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19th February 2011, 02:04 PM	#2
Miniwatt diyAudio Member Join Date: Nov 2004 Location: Den Haag	You have been listening to decades old caps that needed replacing: now you're listening to brand new ones. I'd wait until they have made a few hours

19th February 2011, 10:14 PM	#4
JonHarrison diyAudio Member Join Date: Mar 2004 Location: UK	New caps could have ESR which is too low, do you have a scope to check the supply rails for oscillation ?

19th February 2011, 10:50 PM	#5
tonyptony diyAudio Member Join Date: Mar 2006 Location: New Jersey	Jon, the main power supply rails? If so then yes, the fellow who did the work checked the rails afterwards on a scope. He did not indicate there were any problems. Maybe I should ask specifically about this.

19th February 2011, 10:57 PM	#6
JonHarrison diyAudio Member Join Date: Mar 2004 Location: UK	Yes, check the rails wherever the capacitors were replaced (with the unit playing).

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