On Mon, Jun 5, 2017 at 7:35 PM, Ray Arachelian <r...@arachelian.com> wrote: > On 06/05/2017 11:40 AM, Ethan Dicks wrote: >> The power connectors on many PETs are burned - the current draw is a >> bit much for the connector so oxidation happens which increases >> resistance which adds heat and the cycle repeats... >> > Gotcha, that makes sense, and I take the original connectors are > unobtainium (or will just cause the same issue) hence the alternative > connectors.
Connectors with those spacing are still standard. FWIW, the same sort of thing is common with 3D Printers and heated beds - pulling more power through than the connector really can handle (and aggravated by the intentional generation of heat on the 3D Printer bed which accelerates the process). >> Those aren't power transistors. Those are regulators in TO-3 packages. > I'll see if I can test it and possibly get a replacement. Shouldn't be tough to find those. > It does look > like some of the solder points are a bit burned, possibly by end user > attempted repairs, or maybe power issues. Burns on the plastic power connector or the pins are common. Burns on the PCB under the regulators aren't unusual. Burns right at the solder points sound like poor replacement technique. The traces and through-holes are fairly sturdy there, so that's the one place I _wouldn't_ expect to find burns from operation. > This pet had a printer interface installed in it, the end user soldered > bunches of pins off the IEEE interface to a ribbon cable on both the top > and bottom and then to an IEEE M/F card that presumably went on the > IEEE488 port previously. There's also a DB25 on the side where the > secondary tape interface is (which is now covered.) Hmm... sounds kind of dodgy. > Removing these two did not get rid of the short, so most likely it's in > the power section of the board. Also check the tape drive power transistors (TO-220 packages near the back). Those could give you some grief if they were shorted out. ISTR the regulators are riveted in. If yours are not, it shouldn't difficult to unsolder them and check the resistance from the outputs to ground. I think there should be a couple of +5V supplies, a +12V supply, and a small (TO-220) -5V supply for the DRAM. That is probably not at fault, but if all the others check out, check that one. Do not power up the board with the -5V regulator removed and the DRAM installed. IIRC, the 4116s will _not_ like missing the -5V. > Very true, I was one of those kids back then. :-D Though to my eye, I > don't see the PCB pads worn at all, so more than likely it's the rubber. It probably is. I only mention that because it _can_ happen. >> Outside of actual damage to the PCB, it should be cleanable with >> alcohol. The pads are carbon-infused rubber. Look at the pads for >> indentations/marks. > Sounds like a plan. It seems to be keys 1-7. 8 works if I hold it down > with a lot of force for a couple of seconds. > I'll check the schematic to see if that counts as a whole row in the kb > matrix Yeah... If any of them work, then it's probably not a component. . >> An entire row could be a bad wire or bad trace or a bad component on >> the PET. > Where can I find parts these days if I need'em? Digikey? Maybe... I tend to buy vintage parts from places like BG Micro, Unicorn, Futurlec, and other places that carry obsolete parts. You have to hunt for them. Many of the same parts are needed by folks that repair vintage video games and pinball machines. Check those lists for suggestions. -ethan
