DCC900 still not happy with new capacitors

Recorders, Players, etc.
#1

My DCC900 was playing with dropouts to sound, especially when first switched on. Sometimes there would be no sound at all, and no readout of track titles, until it have been left playing for a while. It would then play reasonably well but not usually perfectly.

So I replaced the electrolytic capacitors on the read/write board and digital board (except the non-polarised ones which meter out perfectly). The other capacitors were all terrible and needed replacement. The boards were cleaned with IPA, including between IC legs were there was some contamination. Surface mount capacitors were used except for the four 68uF capacitors on the read/write board, after consulting the schematics I was happy to replace those with 100uF components.

The result: Exactly the same! It will play fairly well, sometimes perfectly, if left running for a while. But from cold there are still lots of dropouts. I’ve checked the VCO Free Run 7.5MHz signal on J442 of the PZ03 digital PCB, this looks correct even when the machine is dropping out. Are there some other areas that I should be checking?

Thanks for any help.

(This will eventually make it to my YouTube channel youtube.com/video99couk and of course I will link to this forum, web site and videos.)

#2

Welcome to the forum.

Have you checked with a regular analog tape?
If this has a lot of W&F the belts and pinch rollers might need another look. How about Using the service mode? Are all tracks on the head ok?

Ralf

#3

I think I may be getting closer (though I will try an analogue tape later):
I found the problem was thermal. If I cooled down the Read/write PCB then errors would get worse. If I warmed it up then they would clear. I then operated the deck when partly out of the machine so I could get to the capacitor side of the board with freezer and heat gun. The two non-polarised 4.7uF capacitors (which measured fine on my ESR meter) were temperature sensitive. I should have changed them! Replaced and at the moment it’s looking good. I got just one error but I don’t think the deck is supposed to be used wobbling about on its side.

I need to re-assemble and test some more. Will report back.

Regards,

Colin

#4

Great that you mention this.

Lots of discussions in the past about why we always recap everything including both 4.7 caps.

This again proves that while you have it on the bench, you really should do those as well.

Hope it all works out.

Ralf

#5

Yes, lesson learned! The only one I’ve not changed yet is the 2.2uF non-polarised on the digital board, I’ll order one of those in.

It’s playing perfectly now. However if I bash the cabinet (fairly hard) during playback, it will momentarily drop out. Is that normal? I don’t know how robust it should be.

All the best,

Colin

#6

Hi,
Yes that is fairly normal.
Only the portables would be able to take that banging.

#7

Oh no. After playing flawlessly earlier on, it’s now dropping out every few seconds, quite cyclically. I’m starting to lose any hope with DCC. I don’t know what more I can do with this machine. :weary:

#8

The heads can get dirty quickly. Try cleaning them again. Also pinch rollers could be the issue.
What does the Service mode say? You did not answer that question previously. Are the same tracks failing on the head?

#9

Not yet tried service mode, will have to look that up! Don’t yet know how to do that.

It seems to play better in the B direction than A, but both drop out.

There’s still that one non-polarised capacitor on the digital board as well.

#10

Are the red seals on the head still intact? Maybe someone has tried to adjust the head.
Service mode for the 900. Hold Stop and Play and then power on.

Ralf

#11

The left hand screw (B?) seemed very tight and secure. The right hand screw (A direction I think) seemed to be slightly free to move.

I don’t have the remote but using the service mode to look at all channels, in B direction they are reading zeros fairly consistently, with 1’s appearing just momentarily. In the A direction there are much higher readings. I will very gently tweak the right screw to see if it gets the errors down. Otherwise, I suppose the A direction pinch roller is suspect. I don’t suppose they are available?

Thanks for all your help so far.

Regards,

Colin

#12

In service mode, it’s apparent that the errors are happening in time with the left (A side) pinch roller rotation.

#13

We have new ones in stock if needed.

Ralf

#14

I think I will need a pair of pinch rollers. I’ve seen the video, they look easy to change. I’ll include this on my YouTube video too!

I will email you off list.

Thanks and regards,

Colin

1 Like
#15

A post was split to a new topic: DCC300 problems

#16

The new pinch rollers have arrived and I will install them today, though as it happens there are no errors from DCC today. Thanks also for the DCC recording.

I had mentioned that one of the head azimuth screws has not very tight, and though it is set for very few errors on DCC, I thought the best way to align it would be to tune for maximum treble on a good pre-recorded analogue tape. However I found that there is no analogue playback! Just a very faint “whirring” sound, which is reduced when Dolby is selected (so everything from Dolby circuits onwards is working). Have you ever encountered a lack of analogue playback? I suppose it’s not important but it would be nice to get the deck working properly.

#17

Hi,
Yes around the pins (I believe 16-18) are on the read write board holding the flat cable and directly under The 68uF capacitor there could be connection problems from side a-b on the board.

Ralf

1 Like
#18

Well done for that tip! One of those two pins was open circuit at the through-plated hole next to the connector. I patched it with wire and have put the PCB in an ultrasonic tank to hopefully clear any remaining capacitor gunge. I’ve also fitted the 2.2uF NP capacitor you kindly supplied.

Next is to fit the new pinch rollers, hopefully I can do that later this evening. All of this will be on my YouTube channel in due course.

All the best,

Colin

2 Likes
#19

New pinch rollers installed, but that wasn’t so easy. The right hand pinch roller assembly got stuck and would not fully lift off, so I had to replace the pinch roller in-situ, which was fiddly. The left assembly came off fine, but removing the screw on the top cover assembly was hard. In the end though it was playing DCC tapes very well, delighted with that.

Analogue playback though didn’t go so well. I patched out the defective through-plate hole you had suggested, but still no analogue playback (the whirring sound may have stopped though). I checked for further bad through plating and may have found one, but one side is under the flat cable connector, so I can’t get to it. There’s another suspicious looking one next to a capacitor I had changed, and I suspect others on there too. It’s looking too risky to carry on. It works for DCC now and I think I should probably quit while I’m ahead and leave analogue playback, which I would never have used anyway.
However if you ever have a scrap read/write board which hasn’t been eaten too much by capacitor juice, do let me know.

I’ll be putting all my work on YouTube as soon as I have time to edit it all together.

All the best,

Colin

#20

Normally, replacing pinch rollers should ge relatively easy.
glad it worked out. Unfortunately we do not have aboard that you would consider useable.

Looking forward seeing the video.

Ralf