My Attempt at Predicta Restoration

[bandersen]

Nice job I notice you left the old couplates in. I've heard some guys rebuild them. I just picked up a Predicta and it's running fine with the originals. I wonder how prone they are to failure

[PredictaNoob]

Originally Posted by bandersen

Nice job I notice you left the old couplates in. I've heard some guys rebuild them. I just picked up a Predicta and it's running fine with the originals. I wonder how prone they are to failure

I bought a complete set of good used ones from Ross Marshall, just in case.

[DaveWM]

1st turn the brightness all the way down, and check the 220k resistor that goes to the brightness grid on the CRT to make sure it is not open.

Predictas are known for bad tube sockets, if the vert tube is lighting up, then try it while wiggling the tube around.

Check the primary of the vert out transformer.

check the pin resistance of the 6DR7 tube to the sams values

425 to the 275v
2.1 meg to ground
2.1 meg to ground
.1 to ground
0 to ground
3.5 meg to the 275v will vary depend on control setting
68k to ground
50k to ground will vary depne on control setting
450 to ground will vary depending on setting
1000 to ground



Check voltages at the tube pins, this is where a socket extender comes in handy.

[Phil Nelson]

Originally Posted by bandersen

I wonder how prone they are to failure

I think the answer is "sort of." My understanding is that the capacitors inside are paper. I replaced one (K4) preemptively on my Predicta, having been told it was a troublemaker. The others are working fine, 10-odd years later.

Some folks replace all of 'em, some folks replace none. I guess I would consider [A] how well your set's working now, [B] whether you plan to do other work requiring removal of the big PC board, and [C] how much you hate the idea of possibly removing the board only to replace a failed couplate.

How's that for not really answering your question

Phil