I've owned a Commodore PET 8032 for many years. When I first received it, I powered it on for a little bit to see that it worked and haven't really used it since. Which is a shame on my part.

I'm thinking about tinkering with it this weekend.

I've learned quite a bit more about electronics since then and I've been restoring other machines recently.

So, other than that giant capacitor and the AC transformer, what else do I need to be careful of before (and after) I power this thing on?

I'm going to give it an initial inspection before I put power to it. To see if any caps leaked. But that CRT and other AC circuitry is beyond me.

Thanks for any advice.

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Cat; the other white meat.

Electrolytic capacitors are your main concern in old electronic devices. Most everyone knows that old electrolytics can dry out after a number of years of no use and then fail upon being powered. Fortunately, capacitors usually can be replaced without a lot of difficulty.

I wouldn't worry too much about the power transformer. Those things can last for many decades and usually aren't affected by long periods of non-use. On the other hand, the flyback transformer, which is part of the circuitry that develops the high voltage needed by the CRT's ultor (accelerating or "secondary" anode), could go south at any time. Back in the days when I used to fix TV sets to produce some extra income, I'd say that flyback failures represented about 20 percent of all failures I encountered. I'm not trying to scare you, just alert you to a possible problem that could arise.

If you want to be extra cautious before you power the unit, disconnect the ultor lead from the CRT and carefully clean the CRT's surface around the ultor connection. The best way to do this is to spray some glass cleaner on a lintless cloth and then wipe the glass around the ultor connection. Do not spray glass cleaner on the CRT itself. After cleaning around the ultor connection, use a can of "air" to blast the ultor socket and clear it of foreign matter. Before reconnecting the ultor lead, clean its rubber boot with glass cleaner and your lintless cloth. Following this procedure will eliminate the likelihood of arcing around the ultor connection, which could take out the flyback transformer if it does occur.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

A quick search of CRT safety showed up a few points:
- if the unit has been powered up at all recently, the CRT could still have a dangerously high voltage and it should be carefully discharged to chassis ground (that is, to the chassis.)
- the CRT is fragile around the neck and connector; wear eye protection in case of implosion.
- until the unit is discharged, work only with one hand and do not wear or use a grounding strap.

All good points, especially in mentioning the fragility of a highly evacuated CRT. I can tell you from first-hand experience that when a CRT implodes it sends glass flying everywhere at high velocity.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

I used to work on the original 9" Macs, which had the power supply and CRT all in the same box as the main board. We always discharged the CRT, which was the standard advice at the time. This removes the high voltage at the tube, but looking into it now people say that the voltage there is not that dangerous. I did sometimes get an impressive spark out of them though, so it certainly seemed safer to discharge it. The safest thing of all was to only work on a CRT that had been powered off for a long time and all the high voltages had dissipated on their own. Often that wasn't possible as you needed to look at the fault just before fixing it, especially if it was realigning the display or something like that.

We had a special tool with a large high voltage resistor in it to reduce the discharge rate, but I also used to do it with a screwdriver with a wire attached to it. I'd clip the wire onto a good close ground point. I'd then slide the screwdriver under the plastic cover of the anode (a large wire that connects into the glass of the CRT about halfway from the front to the back). Once you touch metal there, and if everything is conducting, you will ground the anode and discharge any remaining charge and the CRT should be safe to work on.

The best thing to do is to stay away from any potential high voltages if you can.

Yup. The screwdriver attaches to a wire which attaches to chassis. But don't do it with a screwdriver attached to a resistor attached a wire which attaches to chassis. In the first case you're handling an object (the screwdriver) that's grounded. In the second case you're NOT.

I agree. Although the voltage is very high, the residual charge stored on an unpowered CRT would dissipate in a split-second were you to come in contact with it. In other words a sustained current is impossible.

However, even a brief shock is enough to make you jump violently. That alone is dangerous if you happen to be holding a tool or if you're near a sharp object (such as a metal CRT chassis).

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Unfortunately, I didn't get a chance to work on the PET this weekend.

Been working double-overtime and it sucks.

I will hopefully get to it soon. Thanks for all of the great advice!

_________________
Cat; the other white meat.

The screwdrivers with the resistors usually had a 10ohm or other less than human resistance so the discharge would still flow though it rather than you. The purpose of the resistor was so the spark wasn't quite as big so as to leave burn makrs on the tools.

Round 2.

Wife is away this weekend and I don't have any deployments at work. So, I might actually get a chance to bring the PET out and see if she still works. Fingers crossed.

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Cat; the other white meat.