My Attempt at Predicta Restoration

[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

[andy]

...

[Phil Nelson]

If they're all ceramic, maybe I should change my thinking. How did you check the resistors before digging them out? (Asked another way, would it have been less work to make a new one?)

Phil

[PredictaNoob]

I think I need to address the electrical discharge issue before I go any further. In my best estimate, it appears to be emitting from the crimp connector on the HV. It arcs to wherever on the chassis with a loud 'pop' starting about 30 seconds after power up, then pops about ever 5 - 10 seconds. I'm not sticking my hand in there until I can fix this. I got struck by lightening in 1986, and I don't care to relive the experience.
Does this problem sound familiar to anyone? (the discharge problem, not the getting struck by lightening problem)

[DaveWM]

not sure where the crimp connector is, but have nver had a pop sound.

you could try backing off on the horz width control/and checking the hot cathode current.

[Phil Nelson]

I was going to ask what you mean by "crimp connector," but Dave beat me to it. Perhaps you could call it out on one of the pictures you have posted.

If you power it up with all the room lights off and watch carefully, can you see the arc?

Phil

[PredictaNoob]

Its here:


I'll try it in the dark and let you know about the spark.

[DaveWM]

most have been a way to make leaving the anode to the pic left and just disconnect there when removing the head.

good idea if it works. I would clean around that connector and wire, and dress it differently and see if that does it. my gess is the connector is getting close to the cage and the plastic is not rated for HV.

Maybe a cardboard doughnut near that to make sure it does not get next to the cage?

[PredictaNoob]

Now it behaves differently, and I suspect I was incorrect at where the pop was coming from. This time when I turned it on, I made note that each and every tube was glowing. None of them were going nuts, but they were definitely glowing, including the 6DR7. Wiggling the tube made no difference. I heard a little sizzling going on, and I tracked it to the underside of the board under the damper socket (6DA4) either under pin 2 or 3. It was just a small white spark dancing on top of that solder joint. I'll have to pull the board again to get a better look as that area is covered and difficult to see.
This time there was no activity on the CRT until I turned it off, and the line would appear for a second and disolve to a single point, center screen for 10 seconds or so.

[DaveWM]

check the pin voltages at the crt pin 2,3 and 7 if the CRT

sounds like it is cutoff.

[Phil Nelson]

Originally Posted by PredictaNoob

I used an electrostatic rust removal process to attack the deepest rust spots, using a 6-volt power supply

I meant to ask this question when you posted the photos, but better late than never.

What did you use as a power supply? I have an old trickle charger that I used to recharge my motorcycle battery each spring. Maybe that would work.

Those pieces looked so good after the electrolytic process was done, I'm wondering why you then went on to paint them. Did they still have pitting where rust used to be?

Phil Nelson

[PredictaNoob]

Originally Posted by Phil Nelson

I meant to ask this question when you posted the photos, but better late than never.

What did you use as a power supply? I have an old trickle charger that I used to recharge my motorcycle battery each spring. Maybe that would work.

Those pieces looked so good after the electrolytic process was done, I'm wondering why you then went on to paint them. Did they still have pitting where rust used to be?

Phil Nelson

That is exactly what I used, a 6-volt trickle charger; hooked the leads to a short length of wire attached to some super-cheap copper alligator clips (since they get destroyed in the process). I went ahead and primed and painted the pieces because I've found that even though the rust is removed/replaced, the 'aged' spots will quickly rust again with a vengeance. There was some pitting, but that was there before the process. Typically, whatever is present stays in place and will be replaced by the ferrous compounds. If the rust has left pits, it will remain pitted.

On an aside, years ago I found an 18th century toy gun outside of a castle in Rhineland-Pfalz. It was a rusted ball, that I thought was an actual gun. I worked on that thing for weeks, electro-bath, dental pick, again and again. After a few days, it was clean enough to recognize as a toy gun. Finally, I was able to free up the firing mechanism. I've been a believer in this process ever since.

[PredictaNoob]

OK, so its time for a break. I need to walk away from this thing for a few days before I hurl it out the third floor window. I have not been able to track down exactly where the problem(s) is (are). I think a breather will do me good.

We're driving over to the Normandy region of France on Monday for the D-Day remembrance activities. Last year I had the honor of buying an honest-to-goodness 82nd Airborne paratrooper veteran a beer in the square of St Mere Egliese. Right smack in front of the church with the replica of PVT John Steele suspended from the steeple from a parachute. If you've every seen "The Longest Day", you know the one I'm talking about. I hope to re-live this feat again this year. And I'll be buying myself a few of those beers as well. My wife also took a picture of me looking out of the observation port of the same bunker the German officer who first spots the invasion fleet was looking out from in the movie. Might try that again, but a little more in the exact spot this time.
I'm bringing along a uniform in case I have the opportunity to 'strap hang' with the 173rd ABN BDE and get to jump into Normandy. Granted, its been 15 years since my last jump and my wife will probably kill me, but who could pass up an opportunity like this, if it presents itself? Who knows?
Anywho, see you all in 8 days or so.
Bob

[batterymaker]

Originally Posted by PredictaNoob

I don't have selection in Power Point. Could you send me an example?

I'll have to get my portable hard drive and post an example.

[DaveWM]

Bob and progress, it has been more than 8 days...