Commodore PET 2001 voltage regulators

[ajgriff]

I've just checked and the deflection coils are hard wired to the PCB.

Alan

[SiriusHardware]

Looking at this image from John Earland's PET 3016 repair thread a while ago, it looks as though it would be quite difficult to wiggle the tube out past the taller components like the LOPT and the long metal tab projecting down from the 'lid' and so on.

Is the monitor housing a welded trapezoidal 'box' with only the rear plate removable, or do more of the panels, the top panel for example, come off as well?

[ajgriff]

Welded box I'm afraid. Looking at the photos (attached) from Colin's account of the restoration it looks like he managed to release the PCB before tackling the CRT ie, the reverse of my suggestion. Also notice how the top tab is bent upwards to provide additional clearance. Can't tell whether this was done for dismantling or reassembly.

Alan

[SiriusHardware]

It looks to me as though those hexagonal standoffs (third picture) could have unseen screw heads which can be unscrewed on the bottom of the housing to remove the PCB complete with the hex standoffs. The standoffs are certainly not permanently attached to the bottom of the housing, as we can see from their absence in the second picture.

We should probably just wait until Colin or Retromit can confirm things one way or the other. If the PCB can be detached easily I would still favour removal of the whole lot in one lump without unwiring anything.

[ScottishColin]

My wiring was unpluggable from the monitor.

Colin.

Originally Posted by SiriusHardware

It seems unusual for the deflection yoke wiring (the wiring to the large copper coils around the rear of the tube) not to be unpluggable at the PCB end, but I don't have one here to look at. This is where we need Colin: What did Colin do?

[SiriusHardware]

Hmm. 3000 series may have a different version of the monitor PCB to AJ's earlier machine, then? There are about three different monitor circuits on the Zimmerman site.

[ScottishColin]

To try to answer the questions above:

a) I did (carefully) bend the top metal 'tab' to allow removal of the CRT
b) The wiring on mine was unpluggable from the back of the CRT - I removed it after I discharged the tube
c) I then removed the PCB before the CRT. There are two screws at the front of the CRT (see photo) which can be easily removed and two plastic standoffs at the back which can be removed by squeezing them (behind the capacitor on the attached photo) either with your fingers or long nosed pliers
d) then I unscrewed the four Phillips screws which secure the monitor and carefully pulled the monitor out.

All then reversed to put it all back together.

Hope this helps.

Colin.

[ScottishColin]

Here's a photo of the wiring carefully unplugged from the back of the CRT.

Colin.

[SiriusHardware]

The wiring on mine was unpluggable from the back of the CRT

From this, I would say you are probably referring to the tube neck PCB. We were wondering whether the four wires going from the PCB to the copper coil assembly (=deflection coils) on the back of the tube can also be easily disconnected?

We're still not sure whether you were able to completely disconnect the PCB from the tube, including the deflection yoke wiring.

Edit, yes, from the previous post it seems you meant the tube neck PCB which can usually be unplugged in just that way. But what about the wires going from the PCB to the deflection coils, did you ever disconnect those and if so how?

[ScottishColin]

Apologies - I've just been to take another look and you;re right - they're soldered both ends.

My recollection is that once I had unscrewed the PCB, I could jiggle it out of the way enough (whilst still connected) to then get the CRT out.

Photo attached which may help.

Colin.

Originally Posted by SiriusHardware

From this, I would say you are probably referring to the tube neck PCB. We were wondering whether the four wires going from the PCB to the copper coil assembly (=deflection coils) on the back of the tube can also be easily disconnected?

We're still not sure whether you were able to completely disconnect the PCB from the tube, including the deflection yoke wiring.

Edit, yes, from the previous post it seems you meant the tube neck PCB which can usually be unplugged in just that way. But what about the wires going from the PCB to the deflection coils, did you ever disconnect those and if so how?

[SiriusHardware]

Thanks, that's a really good view which seems to confirm that you can't really completely separate the tube and the PCB without unwiring / unsoldering the deflection coils, but it also seems to show that you don't really need to.

[ajgriff]

Well that was fun! Hope it provides Tim with some helpful guidance.

Alan

[ScottishColin]

It also does rather demonstrate that when some of you say things like 'deflection coils' you know what you're talking about and I don't....

Colin.

Originally Posted by ajgriff

Well that was fun! Hope it provides Tim with some helpful guidance.

Alan

[SiriusHardware]

One detail we haven't mentioned to Tim, when you come to undo the rubber cap from the tube AFTER discharging the tube, don't try to pull or lever the cap away from the tube. What you have to do is firmly pinch the rubber blob in the middle of the cap with your thumb and first finger, and while squeezing firmly, slide the rubber cap gently from side to side. Apart from the squash pressure being exerted on the 'blob' you don't need to use any force to remove the cap.

When you get it off you will see why - there are two sticky-out hooks which hook under the edges of the hole in the tube - pinching the 'blob' makes the two hooks withdraw inwards towards each other so they can be extracted through the hole.

'deflection coils'

Yes, sorry, we shouldn't make assumptions. Problem is, Colin, we see you as a seasoned pro now.

[ajgriff]

Originally Posted by ScottishColin

It also does rather demonstrate that when some of you say things like 'deflection coils' you know what you're talking about and I don't....

My apologies Colin. I dislike specialist jargon and acronyms too. Must try harder.

Alan

[ScottishColin]

No need to apologise. I'm still learning every day from you lot and I appreciate it.

Colin.

Originally Posted by ajgriff

My apologies Colin. I dislike specialist jargon and acronyms too. Must try harder.

Alan

[retromit]

Once again, many thanks for the advice a help - and I might apologise for the lack of interaction in the post; it's been a bit manic at work. I'm so pleased it's the weekend!

Well, I've made some progress. It was something I wasn't looking forward to, but with all the help in the posts I've managed to discharge to CRT and get the CRT/PCB safely out. I went ahead and removed the monitor casing from the main PET case as this made it far easier. The discharge went well, no sparks/bangs/crackles, but I made sure (from the videos Colin posted) that .

After a small about of wrestling with the CRT and PCB, I managed to get both out of the casing, and the CRT is now resting screen down on a towel with the PCB next to it on some books. I haven't removed the end cap from the tube at this point.

I'll post a few more details below with some pictures of the progress. The removal of the CRT is not something I'd really like to do again (especially the discharge), but thanks to your input it made it a lot easier. I'll just be happy when everything is back in place (and working) again.

Tim.

[retromit]

With the CRT out you can really see the amount of rust, so it will be a worthwhile exercise. I started off by sanding this, then rubbing down (especially in all the areas where it was pretty rusty), taking it down to bare metal when needed. When this was done, and it was cleaned a few times, I added on some rust neutraliser.

I'm just waiting for the rust neutraliser to dry, then it should be able to be painted. I'm planning on just putting two coats of primer on with this only being internal.

Tim.

[retromit]

WIth the PCB out, you can see how dirty this is as well (although in the picture, it doesn;t look quite as bad!. There's quite a lot of debris on it too. So I think I'll also gently clean this down with IPA whilst I have the opportunity.

Tim.

[retromit]

With the monitor off the PET, you can see the dirt/rust which had been hidden. I masked off with some tape the opening for the monitor so nothing could fall inside the PET (although I will be cleaning the inside later).

This has been given a really good clean, so you can see the before and after pictures attached. After final cleaning, there are still a few, faint, rust spots; I'm not sure whether to put a drop of the neutraliser on them, or just keep an eye on them (the third picture (zoomed) seems to make them look worse). Looking over the rest of the top it certainly doesn't seem to warrant a respray (to me, anyway), but would welcome any opinions/advice.

Tim.