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Old 11th Apr 2022, 8:29 pm   #21
ScottishColin
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Default Re: Commodore CBM 4040.

It's a 3A fuse.

Colin.


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Originally Posted by Mark1960 View Post
Maybe check that the mains plug has a reasonable fuse, not 13 amp, it might reduce the size of a bang. I wonder if that filter had let out some smoke in the past so someone bypassed it, did you check it for shorts and opens?
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Old 11th Apr 2022, 8:36 pm   #22
ScottishColin
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Default Re: Commodore CBM 4040.

I have tried two different meters; the more expensive one is self-adjusting so there's no ranges to be set and it stays stubbornly at 0.

The other more manual one I set at 2M ohms, and all three checks started at 1 with nothing being tested and stayed there when testing.

Sorry - I added to one of my previous posts; I have solid core mains wire or stranded wiring - is there a preference?

Colin.


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Originally Posted by SiriusHardware View Post
I hope the 'O' on your meter means 'Out Of Range' and not 'Zero'. Make the L-N, E-N, E-L measurements again but with the meter on the highest ohms range it has, if you were not already doing that. If it still indicates very very high or infinite resistance, that's fine.

32 ohms is quite a low resistance but the transformer primary winding wire looks quite thick, so I am going to say yes, try it.
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Old 11th Apr 2022, 8:37 pm   #23
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Default Re: Commodore CBM 4040.

Stranded, and brown, so that it is instinctively understood to be carrying the Live.
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Old 11th Apr 2022, 9:25 pm   #24
ScottishColin
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Default Re: Commodore CBM 4040.

OK - still alive.

Soldered new wire, unplugged all internal cables, switched on and nothing went bang.

What's next then?

Colin.
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Old 11th Apr 2022, 9:29 pm   #25
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Default Re: Commodore CBM 4040.

Up to you, you can try measuring for the expected AC voltages coming out of the low voltage side of the transformer, or switch off, plug the low voltage connector back in, switch the mains back on and look for life signs, especially those voltages which should be on the ringed ends of CR7. CR8, CR9 next to the heatsink. The LEDs on the unit may or may not dance when it powers up. If you find decent voltages on the ringed ends of the diodes, then switch to the plain ends of the diodes, you should find +12V on the 'plain' end of CR7 and CR8, and +5V on the plain end of CR9.

Last edited by SiriusHardware; 11th Apr 2022 at 9:35 pm.
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Old 11th Apr 2022, 9:51 pm   #26
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Default Re: Commodore CBM 4040.

OK - cables reconnected inside. Power on

All three LEDs light for 1 second, then off. Then disk drive 0 spins up for about 8 seconds then spins down.

It all seems OK, but it's difficult to know what is expected - I know what should happen if the drive is connected to a powered on PET - all three LEDs should flash twice, but I don't have a cable.

Voltages as requested

I need Commodore part number 320101 but they seem rare. There's a video here showing someone taking an HPIB cable, chopping off one end and replacing it with a Commodore IEE plug. I'd rather not do that if possible - I'll keep hunting.

https://www.youtube.com/watch?v=1PTVsby1GCo&t=3s

CR7 - 11.66
CR8 - 12.10
CR9 - 5.18

I've attached a photo to make sure I have checked the right end of CR7/8/9.

Colin.
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Old 11th Apr 2022, 10:02 pm   #27
SiriusHardware
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Default Re: Commodore CBM 4040.

Yes, without doubt those voltages are good and the unit seems alive enough to make the outlay for a matching cable worthwhile. Still a mystery over why the mains wiring was such a dangerous mess.

There is a really comprehensive servicing document for these, but I hope your German is good. If not we'll just have to muddle through as usual. The main thing is not to disturb anything mechanical without a reason, as the head alignment in particular would be very difficult to set up again without the specific gear to do it.
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Old 29th Apr 2022, 6:34 pm   #28
ScottishColin
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Default Re: Commodore CBM 4040.

Update - after a bit of time I've managed to source a cable from Dave Duke for a very reasonable price (I'd recommend him to people for PET parts). I had a couple of mechanical issues that needed work, but now they're done, I've just fired it up tonight and somewhat miraculously, both drives work and I can read directories and read programs from disks. I have yet to test any writing.

This leaves a couple of things:

1) cosmetic (paintwork) work, but I'm Ok with that after the PET restoration

2) diskette drive maintenance - specifically the pads and and greasing/oiling that may need to be done to a 40+ year old pair of diskette drives.

Has anyone worked on old floppy drives before and done any maintenance work?

As an aside, the case has A.E. Hill written on the back. It would be nice to think it was this chap:

http://www.computinghistory.org.uk/c...D.%20Tomlinson

Thanks for all your help again.

Colin.
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Old 29th Apr 2022, 6:42 pm   #29
SiriusHardware
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Default Re: Commodore CBM 4040.

I'd say the odds are long against it not being the same Mr. A.E. Hill. Glad the unit is essentially working, about time you had a bit of luck, I think.

I think TonyDuell is going to be your man to ask about physical maintenance on the drive mechanisms.
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Old 29th Apr 2022, 7:00 pm   #30
ScottishColin
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Default Re: Commodore CBM 4040.

I know - but I prefer the romantic view that it might have been.....

Colin.


Quote:
Originally Posted by SiriusHardware View Post
I'd say the odds are long against it not being the same Mr. A.E. Hill. Glad the unit is essentially working, about time you had a bit of luck, I think.

I think TonyDuell is going to be your man to ask about physical maintenance on the drive mechanisms.
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Old 29th Apr 2022, 7:42 pm   #31
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Default Re: Commodore CBM 4040.

I think my tortuous double negative may have allowed some room for confusion. I'm saying that it is highly likely that they are one and the same person.
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Old 29th Apr 2022, 9:25 pm   #32
ScottishColin
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Default Re: Commodore CBM 4040.

Aw. See? You're an old romantic too.

Colin.


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I think my tortuous double negative may have allowed some room for confusion. I'm saying that it is highly likely that they are one and the same person.
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Old 1st May 2022, 12:06 pm   #33
ScottishColin
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Default Re: Commodore CBM 4040.

I got in contact with Tony about drive maintenance via PM and he was kind enough to answer and allow the answers to be placed here for others to see:

"Are these the ones with the flat head positioner cam with a spiral groove in it? Not my favourites...

I seem to recall that the 390 is essentially a Shugart 400 without the PCB, for customers like CBM and Apple who wanted to use their own electronics. So the Shugart 400 service manual may be of use.

But anyway. IIRC the spindle bearings are sealed ball races and if they turn smoothly they should be fine. But put _1 drop_ of light oil (sewing machine oil, for example) on the bearings at each end of the spindle motor. Clean the belt and pulleys.

A bit of dry ptfe-based lubricant on the head carriage rails is not a bad idea. And if you can find a plastic lubricant (silcone based), a little on that positioner cam will help.

Other than that, clean them! Dust is the main problem, not just dirty heads."
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Old 1st May 2022, 12:08 pm   #34
ScottishColin
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Default Re: Commodore CBM 4040.

My reply:

"I'll pop a drop of Singer oil in as suggested. The thing (I'm sure it has a better word) that went into the spiral groove had broken on one of the drives and I soldered a small ball bearing to the brass part but it seems to be working ok.

I've already put some ptfe lubricant on the rails. Do you have any suggestions re the felt pads? Is is simply a matter of cutting some felt to the size and sticking it in?"

Colin.


Quote:
Originally Posted by ScottishColin View Post
I got in contact with Tony about drive maintenance via PM and he was kind enough to answer and allow the answers to be placed here for others to see:

"Are these the ones with the flat head positioner cam with a spiral groove in it? Not my favourites...

I seem to recall that the 390 is essentially a Shugart 400 without the PCB, for customers like CBM and Apple who wanted to use their own electronics. So the Shugart 400 service manual may be of use.

But anyway. IIRC the spindle bearings are sealed ball races and if they turn smoothly they should be fine. But put _1 drop_ of light oil (sewing machine oil, for example) on the bearings at each end of the spindle motor. Clean the belt and pulleys.

A bit of dry ptfe-based lubricant on the head carriage rails is not a bad idea. And if you can find a plastic lubricant (silcone based), a little on that positioner cam will help.

Other than that, clean them! Dust is the main problem, not just dirty heads."
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Old 1st May 2022, 12:08 pm   #35
ScottishColin
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Default Re: Commodore CBM 4040.

And Tony's further reply:

"My worry about the repair to the follower on the head cam (the little ball bearing) is that its position determines the radial position of the head and that you have to be accurate to rather better than 1/48". If not the drive will work fine, but disks formatted in that drive will only work in that drive. With a dual disk drive that is rather inconvenient -- you can't use the same disks in both drives!. Doing the radial alignment is an entertainment on 'normal' drives, quite how you do it on one of these I can't remember.

As for the pressure pad, most of my drives are double-head so I don't have much experience, but a bit of felt cut to size and stuck it should be fine. Look those felt pads sold to prevent scratches on furniture, for example."
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Old 1st May 2022, 12:11 pm   #36
ScottishColin
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Default Re: Commodore CBM 4040.

Here's what broke - the head cam that Tony refers to - I soldered a small ball bearing to it and it now works. Next I need to test writing on one drive and reading from the other as Tony suggests.

Colin.
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Old 1st May 2022, 1:05 pm   #37
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Default Re: Commodore CBM 4040.

I don't think the ball bearing should be soldered (or otherwise fixed) in place. It locates in the dimple in that spring leaf (which is fixed to the head carriage) and runs in the groove in the cam.
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Old 1st May 2022, 1:25 pm   #38
ScottishColin
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Default Re: Commodore CBM 4040.

Sadly the end including the dimple had completely gone - all that was left was a half-circle area where the old part was so I soldered into that part.

The ball bearing now runs in that cam on the brown disc.

Colin.


Quote:
Originally Posted by TonyDuell View Post
I don't think the ball bearing should be soldered (or otherwise fixed) in place. It locates in the dimple in that spring leaf (which is fixed to the head carriage) and runs in the groove in the cam.
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Old 1st May 2022, 1:49 pm   #39
SiriusHardware
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Default Re: Commodore CBM 4040.

It sounds as though it would be worth keeping a patient eye out for a Shugart 400, ideally one with broken electronics, as a parts donor. It's not ideal for the problem to be something which directly impacts the head tracking but as you have a second, and presumably working and aligned drive, then you could as a last resort put discs made on that drive and minutely adjust the head tracking position on the other drive until it is consistently able to read the discs written by the other drive. Not at all ideal, but if you have no other option...

From what you said earlier it sounded as though both drives were able to read discs successfully, did something go wrong since then?
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Old 1st May 2022, 1:50 pm   #40
ScottishColin
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Default Re: Commodore CBM 4040.

I've just checked - I can load a file from Drive 0 and save it to another disk in Drive 1, clear the PETs memory load it and run it. And vice-versa. So I think I've got lucky here.

I fully expect this to be inconsistent as time goes by, but right now it's doing what it's supposed to.

I have some more diskettes coming so I can practice copying whole diskettes from one drive to another to see what happens then too.

Colin.
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