really stupid mistake -w- CDP focus offset adjustment - diyAudio
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Old 19th December 2007, 10:49 PM   #1
pjanda1 is offline pjanda1  United States
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Default really stupid mistake -w- CDP focus offset adjustment

I've got my new/old Philips 630 apart, and I just completed the NOS mod. When I was putting it back together, I put a screw into what looked like a hole that needed one. Oops. It was the focus offset adjustment trim pot. I just have turned it a hundred times before I figured out what I had done. I assume in addition to screwing the pot, I've completely screwed my player. Is that true?

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Old 19th December 2007, 11:50 PM   #2
pjanda1 is offline pjanda1  United States
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Is there any chance to pot is still good after being turned a whole bunch of times? I could take it to a tech and have them adjust it. I don't want to spend much $$, as I've only got $25 in the player. Could I replace the pot with a fixed value resistor? It sound like not all players have these.

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Old 20th December 2007, 10:31 PM   #3
kevinkr is offline kevinkr  United States
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Did you actually damage/destroy the pot? Have you tried to play a cd since this incident?

Why not just figure out what the value of the original pot was and buy one from mouser or digikey. (They should have something that physically and electrically fits.) You'll have to tweak until you find the right value that allows it focus properly, but that shouldn't take too many hours. You might start with it centered and move it a little at a time in one direction until it either works or it doesn't in which case go back to center and go the other way.. Other algorithms work as well, my assumption (risky) is that the pot "should" be relatively near the middle with a typical bogey device.. YMMV
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Old 20th December 2007, 10:38 PM   #4
pjanda1 is offline pjanda1  United States
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I gave up and took it to the shop. I didn't know if adjusting by ear would be ideal. I would have always wondered if I had it right. I probably should have gone for it, but its too late now.

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Old 21st January 2009, 03:37 PM   #5
pjanda1 is offline pjanda1  United States
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I finally got this CDP working again, and I figured I'd complete the story in case someone else experiances a similar problem. The saga had continued here:

this 22K trim pot

Basically, the shop couldn't find a replacement pot and I took the machine back. I found a pot with a different rating but same footprint sold as a bias trimpot for a marshall guitar amp. I tacked it onto an AES order a few days ago.

So I soldered the pot in and it works! Without moving the pot it would read a few CDs, but would badly skip and struggle on others. I turned it one direction and it got worse. The other direction it got better. Now it reads most everything. If it skips on a disc, I open and close the door and all seems to be well again. I picked up a cheap old Tek scope. When I get it running I assume I'll be able to more precisely adjust the focus pot.

The CDP sounds quite a bit different with the NOS mod than I remember it sounding stock. Stock, it was dark and a little cloudy. Either way, the old Philips has great PRAT (I know not all of you will believe in such a thing). Now though, it is tonally more open and extended. My Philips 963SA (stock) sounds more fleshed out in the mids and bass transients are sharper. However, PRAT is more sluggish. The highs midrange attacks sound less defined and smeared in comparison to the old 630.

Now that it is working, I plan to leave it alone for a bit and complete some other projects. Then I'll return and upgrade the output stage. I'm pondering several options. I've got a nice regulated +/- 15V supply. I also have a pair of mic input transformers. Then again, I might just swap the opamps and coupling caps and call it good.

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