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PET 4032 restoration

JonB

Veteran Member
Joined
Jan 26, 2014
Messages
1,652
Location
South Herefordshire, UK
Well, here we are with another poorly PET for restoration.

I'm going to document its return to PET loveliness here.

The back story is a 4032 PET bought without a transformer which did not survive shipping terribly well. I posted pictures in this thread http://www.vintage-computer.com/vcforum/showthread.php?50757-Smashed-up-4932-PET and I would like to say that the seller was very fair about it.

So here we are, then. What needs doing?

  • Dismantle and clean the case.
  • Refurbish the keyboard.
  • Replace smashed-up CRT.
  • Replace missing transformer.
  • Replace mains filter choke / capacitor (looks like it's had some magic smoke escape).
  • Respray metal parts that have rusted (CRT chassis and bottom case).
  • Clean PCBs. I'm saving that till last!
Hopefully the motherboard is OK electronically speaking and it will boot. It's a "fat" 40 with a 12" CRT that appears to have been upgraded to 8000 series spec with a 64K memory upgrade and Microport 80 column upgrade ROMs. All very intriguing!

Other related threads:-

 
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The CRT case rear was whacked in transit and as a result suffered some damage. With careful manipulation of the cracked sections, I was able to restore a degree of normality, although the cracks are still visible.

CRT Case crack.jpg CRT Case repair 2.jpg CRT Case repair.jpg
 
After a good hard scrub, the top case and CRT cover are looking much better.

Cleaned top case.jpg

That paint finish is really tough, so I felt confident using various household cleaning products and a stiff brush. The last stains came off with an abrasive cleaner called "Barkeeper's Friend" - you can also use an abrasive cream like Cif. I had to leave some rust stains on the top of the case because I didn't want to break through the paint layer accidentally. Once assembled, these can't be seen so it is OK.
 
Typical keyboard dismantling and scrubbing....

Keyboard cleaning.jpg

In the plastic jug is a hot solution of Flash all-purpose cleaner and oxygen based bleaching agent.

Keyboard done.jpg

That turned out to be a bad call. The oxygen based agent has attacked the keys and they now look a little matte. So next time, I will only use soap and water!

This is not the end of the world, though. A polish with some silicone fluid like Armour-All should sort the keys out. In the meantime they are all clean, and the PCB contacts and rubber pads got a buff up too.
 
When I received my PET, someone had used some inappropriate cleaner. The keys were very dull and had "permanent" white streaks from a rag.

It took many applications of mineral oil (and a lot of rubbing) to make them look good again.
 
@crock: yep. Although I have no evidence there are any sticky keys.

@KC9UDX: what, you mean engine oil?

I did notice one thing, though. There is no latch on the caps lock key, so it doesn't stay down. This may have something to do with it having an 80 column conversion. I seem to recall reading that this key was repurposed so it is per the 8032 keyboard, but can't remember the details. Anyone know?
 
A bit less rust...

The base is painted with a soft sheen black.

image.jpg image.jpg image.jpg

It's not perfect, but this is a 35 year old computer, and I'm no Michaelangelo when it comes to spray paint.

The CRT chassis was easier. White primer (again, sprayed) which is very forgiving.

image.jpg image.jpg

Again, not perfect but will not be visible when the PET is back in one piece again.
 
Not engine oil! Mineral oil. I think the stuff I have is labeled "food grade wood oil."

It's great for restoring plastics, wood, all sorts of things, including removing stubborn old tape or stickers.

Just don't bathe modern plastics in it.

It's clear, thin, and you can safely drink it. Don't do that though unless you can spend a day or more in the bathroom.
 
Ah, I see, thanks. The stuff is used all over the place we just have different names for it in the UK. So, "wood oil" is used for oiling wooden chopping boards amongst other things. I have some of that, though it isn't particularly thin. But it turns out that baby oil (made by Johnson & Johnson for moisturising baby skin) is also made of mineral oil (and perfume, but..) and it is light and thin. There may be some of that lying around here somewhere.
 
Right... OK... the next thing I want to discuss is cleaning the PCBs. Better post some pictures first....

Main board with 64K expansion daughter board. It's plugged into the CPU socket and you can see the Microport ROM at UD7. I'm not sure what the other (non standard) ROM at UD11 is, or why there is a sticker on the chip at UA3 (but it looks non standard, too).

image.jpg

The CRT board might be a thought of as a little better.

image.jpg

But back to the main board. It is covered in a thin layer of black dust that seems to have stuck to it. Obviously cleanable, but underneath, the protective lacquer that you expect to find on these PCBs has gone dull, almost like it was sprayed with matte varnish. Is this normal on the Universal PET boards? Here's a picture of a section I have cleaned with soap and water.

image.jpg

Speaking of which, I am very reluctant to put any of these boards in the dishwasher / a bowl of hot soapy water. Especially the CRT board (but I would remove the flyback transformer and T711 first). Is it really safe? What about the trimmer potentiometers and the choke that controls width?


(Edit: The underside of the PCB is matte. I opened the metal shield box and found matte PCB inside that as well, so I think it came from the factory like this.)
 
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While I'm waiting to decide how to clean the PCBs, I thought I'd try to sort out the rear panel labels. These are metallised plastic stickers that seem to have suffered a bit.

This is the best picture I have. They look kind of scrappy round the edges, because the aluminium film backing has been eaten away, and the chassis paint is showing through.

image.jpg

I thought it might be interesting to see what happened if I peeled them off and stuck them to a silver material, say some aluminium foil. Voila!

image.jpg

image.jpg

Not quite as new, but a big improvement. Just have to cur them out and attach to the back of the PET.
 
Speaking of which, I am very reluctant to put any of these boards in the dishwasher / a bowl of hot soapy water.

I would not. Conformal coating on these boards (if any was used) has long broken down. Water is the enemy of PCBs. If you do, the only way to dry them properly would be in a thermal vacuum station for many hours under high heat and vacuum to dry and outgas the vapor.

Instead use very pure isopropyl alcohol (99%) to clean the boards.
-Dave
 
Thanks Clint, I'll try to rember to take a piccie of them in situ. You can all chuckle at my crack handed gluing!

Meanwhile, the postie arrived with a big box today. So what have we here...?

image.jpg

Sweet little Amstrad GT64 monitor. Off with its back and out with the home made chicken stick. Got to discharge the tube first. Yes, I know, corona rings etc but this is the best I have. Fortunately, not a spark, and I could see it touching the prongs of the HT lead.

image.jpg

Hmmm, that transformer looks useful.

image.jpg

Looks like NightfallCrew got it spot on. The tube fits perfectly (even the mount points) in the PET's CRT chassis.

image.jpg
 
A trial fitting of the front panel. Looks spot on to me!

image.jpg

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And the video board, slightly cleaner (but not much) slots right on in there.

image.jpg

Plug in the loom, and it's ready to go. Oh, apart from the earth strap, which needs to be repaired first.

image.jpg

Testing this will have to wait until the transformer turns up...
 
Thanks, EagleTG!

Now.. onwards, onwards!

A replacement transformer arrived in the post today, care of Clint. Top bloke!

image.jpg

With an enormous amount of fiddling, I wired up the mains side and robbed some posts from an 8050 disk unit I have waiting to be restored. Then I wired the low voltage loom to the secondary winding and fitted it to the chassis.

image.jpg

On with the repaired CRT earth strap and whack the restored CRT chassis on top, securing the four mount points with nuts. Then in with the motherboard and connect the power, keyboard and CRT looms to it. Starting to look good now!

image.jpg

It's all wired up and ready for power up, although it's not entirely screwed together and the CRT back case is still off so I can make adjustments to the video image if necessary.
 
And here it is.

image.jpg

The power switch appears to be stuck in the "on" position.

As you can see, there's no image. The scan and fly back lines are visible though, so I assume the video circuit is initialised. It is certainly responding to trimmer adjustments. On boot up, I get the triple chirp noise, but I don't know if this indicates a successful start or not. This is a Universal PET board and it does have a CRTC; I swapped it for a known working one out of a BBC Micro and got the same result, so I can at least say the CRTC is OK and not causing the problem.

Is there a single BASIC command that would make it beep and prove it has started up? I tried PRINT CHR$(7) and holding the space bar down for a while, no beeps.

What should I check next? There are very few socketed chips and I have checked them to be sure they are in their sockets.
 
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After its been on a while, power off and then in a few seconds back on. Do you see a screenful of garbage characters before it is cleared? If not, something may be wrong with the video signal in addition to other problems. Do you have a scope or voltmeter? If you do see the garbage screen for a moment, it means the video signal is OK, but the PET boot is going wrong shortly after it initializes the CRTC and clears the screen. This may be due to faulty ROM or low RAM or bad traces/connections on the board.
 
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