Astrodome Power Pack Repair

by John Grady

Noel was kind enough to send me some excess parts in various shape from his excess small F pile. As a result, I spent a whole day in basement recovering what I could and learning a lot from defective parts. I saw failures so I decided to share with club.

So first up is Astrodome light pack (AC power supply). What goes wrong here is the white cylinder with Bendix on it. Don’t bother testing since they are either all bad or on the way out. They develop leakage inside and the output volts drop from the 200 + AC you need to make the system work. The volts drop, the display dims and eventually goes out.

In the pictures, before and after, you see a new .1 uF 440 ac yellow cap but a .1 /630 vdc Panasonic radio cap is fine too (Mouser). 95% of the time that is the problem.

Test by putting +12V to the orange wire by a clip lead and – 12V to the case. Put the AC voltmeter clip to the white wire and the other meter wire to same case ground (see test picture) This one put out 250 AC , with 13V in. (!) It will be really bright.

However this one really fought me and still did not work. I won’t bore you with details but after a lot of sleuthing I determined that the power transistor on top was degraded. It was not dead but degraded. It got hot and so did resisters. (Clue!) So I had an old rusty junk 300 radio which uses large size TO3 germanium PNP transistors too (some 300 radio were smaller size). The large size is called TO—3. The NTE 104 is similar but expensive. Anyway, that fixed it. I found many Germanium TO3 PNP on ebay , including 5 for 10$ shown . I bought those. Others sell for $40 each so shop around.

As part of this afternoon I tried modern silicon PNP but they do not work. Unlike a radio, the bias in a switching application is not so critical so any TO 3 PNP germanium ought to work. No insulating washer is needed if you have to change since the metal case is grounded.