DCC730 Capstan motor issue

Hi guys,

I’m in the process of refurbishing my DCC730.
Upon recording on side B, as time progresses , more and more dropouts occur.
By about the middle of the tape (side B) , dropouts are becoming very frequent.
This happens on all cassettes (DCC) I put in the deck. Recording on Side A goes without any issue.

Upon investigating further, I noticed that when running a tape on side B, the capstan motor exhibits regular drops in speed. About once a second, you can hear a little whine from the capstan motor, as it seemingly need to adjust its speed. This does not occur when running side A.

What I’ve done so far :

  • Taken out the capstan flywheels, clean the shafts and relube them
  • Cleaned the capstan belt : there is still sufficient tension on the belt as far as I can tell
  • Applied a small drop of oil to the capstan motor shaft en guide roller
  • placed new pinch rollers

I would appreciate any assistance on what could be causing this, and how to solve the issue. It would seem to me that there is an issue with the speed control / FG servo /… of this motor. Bad caps?

As a background : I have a lot of experience with fully restoring reel to reel decks (including recapping, ugrading transistors etc…) and to a lesser degree cassette decks, so don’t hesitate to go full technical with me :slight_smile:

Edit : I’ve also cheked the reel tables’ motor, and those gears look OK (not cracked). The main black gear between the capstan flywheels has been re-greased after removing the old white grease.

If a video or sound rec. of the issue is needed, just let me know. Thanks!

Well, as far as I know the capstan motor rotates in one direction only, and the way the belt is wrapped around both flywheels of the capstans ensures that both capstans rotate contra to each other.
So only one of the two pinch rollers engages the corresponding capstan, and that determines whether the tape runs in one direction, or the other.
Also the speed of the capstanmotor is regulated by the datastream that comes from the head. If the bits come too fast, the speed is reduced and vice versa.
So if the effect that you encounter is only on side B that suggests an issue with the pinchroller or capstan that is responsible for side B. So maybe some dirt on capstan B or deteriorated rubber on pinchroller B could cause irregular running of the tape.
I don’t think it has anything to do with the motor itself, but please correct me if i’m wrong.

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Hi Pvdm,
Thanks for your feedback ! Hardened pinch roller was my guess as well. Both pinch rollers were replaced two weeks ago with new ones.

Come to think of it… I used a tape that was recorded (with drop-outs on side B) when the old pinch rollers were still in the machine. If the capstan speed is bitstream dependend, than I need to re-test!
I’ll need to make a test recording with the new pinch rollers first, as i don’t have pre-recorded DCC’s.
I’ll report back…

Edit : I’ve recorded a few tracks on side B of a random DCC, and the problem is indeed no longer present! The capstan motor is running smooth now.

So, the clue was in the bad pinch roller present in the machine before, resulting in those cassettes beeing recorded with speed variations larger than what the DCC system can cope with. Those cassettes (only a few), I’ll need to re-record now with the new pinch rollers in place.

Thanks Pvdm for providing the clue on the capstan speed beeing controller by the bitstream!

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Excellent explanation

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Glad I could help.

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This seems to be the culprit causing side B drop outs on my 730!

This is very normal unfortunately , but easy to replace.

We have them in stock. You can reach us drdcc@dccmuseum.com

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As additional info :

The 730 also displayed a lot of “clean head” messages. Sometimes just after cleaning the head.

Upon inspection, the DCC cassettes were sitting pretty loose in the DDU-2113 tray.
During play, the cassette could be moved a few mm back and forth by hand.
I’ve solved this by thightening the DCC cassette in the tray, by slightly bending the small metal latches of the tray keeping the cassette in.

The cassettes are sitting pretty tight in the tray now, and the clean head messages have dissapeared.

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I have exactly the same issue. Playback only effected when playing the B side. The issue gets progressively worse the longer the tape plays. Head and rollers have already been cleaned using IPA.
So would you recommend changing the pinch rollers before I do anything else?

Yes, change the pinch rollers.

I cleaned my old (bad) pinch rollers with IPA as well, and even though they looked very clean and in good shape, the issue wasn’t resolved until the new pinch rollers were in place.

Changing them is rather easy. I carefully popped them out of their sockets using a fine flathead screwdriver. You might want to manually roll the cassette tray out a bit if it makes it easier to access the pinch rollers.

I’ve placed the new ones in with a tweezer to about the right position (pinch roller axle ends at the ‘entrance’ of their guides), and then pushed them in their socket with my finger. They simply click in place.

Very simple job, it takes no more than 5 minutes.

dcc museum offers new pinch rollers. If you live in the Benelux, there’s a guy on 2dehands.be selling new ones as well.

edit : be very careful not to touch the tapehead in any way, and if you don’t have an anti-static wristband, than touch the housing of the deck regularly to avoid static electricity build-up.
If you’re a bit technically minded, you can also opt to take the DDU-2113 unit (semi-)apart for a cleaning and re-lubing while you’re at it

If the above explanation for changing the pinch rollers is not sufficiently clear, then I can post some more detailed guideline with pictures.

I do have the same problem with a DC-10 but it’s on some of the tape, not every tape, and the side B the most. Side A sometimes. When the problem occurs I push the tray up or down. It plays normally again. Please help.

I took your advice and changed the pinch rollers. It was a little fiddly but it has transformed the machine. Tapes that caused issues previously are now playing without any trouble.
Thanks.

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Good to hear that your recorder works again!

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