Predicta Holiday - First power up attempt
 

HI All,

Well, the XYL and I tried powering up the Predicta Holiday last night. Ramped the power up slow and got the tubes to glow. No sound or raster. Everything smelled and looked fine. Could hear a slight noise from the flyback and up at the CRT, a regular beat. Looking at the troubleshooting chart it says power supply is the most likely culprit. So I pulled the HV can off and measured the flyback for resistance. With the can off I can see a drip underneath the flyback.

5-D, 11.6 Ohm out of expected 12.
4-3, 10 Ohms out of expected 13
3-B, 8.6 out of expected 11
L17, spot on, 1.7 ohms

Although it says on the schematic not measure between 5 and the HV output, it gives an expected measurement of 385 ohms. I figured that the do not measure was for older VTVM's, so I checked it anyway, 366 ohms. So the top coil seems good, lower coil a little low in resistance. Shorted turns? When we pulled the HV rectifier tube, it was completely cool to the touch. With the really low filament voltage I am not sure how warm it should be.

So, any suggestions where to start?

Jonathan

I'm pretty sure that warning means not to measure the voltage with the set powered up, because of the presence of high voltage spikes. There should be no harm in measuring the DC resistance when the set is powered down.

Measure the B+ voltage at the output of the rectifier, and on the various power supply rails? Fusible resistor OK?

With the horizontal output tube plate cap removed, is DC supply voltage present on the cap lead?

All those resistance readings are well within spec. Dripping wax is common and no cause for concern. When working normally, the flyback will be a little warm after maybe 30 minutes. Don't expect the set to work until you get to around 110 or more on your variac.

If your TV has all of its original capacitors, I'll put on my magical wizard hat and predict that you likely have a bad capacitor -- and more likely, a few dozen of them.

I wouldn't fret over the flyback at the moment. Some wax drip underneath it is common.

Many restorers would plunge ahead and start recapping, beginning with the (duh) electrolytic capacitors in the power supply. The schematic shows the voltages ("280V source" and so on) that the TV is supposed to produce downstream of the rectifiers and p-s filter caps. Set your variac at 117 volts and test those points.

Until your power supply is producing the basic voltages needed by the rest of the TV, trying to troubleshoot problems on a symptom-by-symptom basis can be frustrating and confusing.

What have you done to this TV up to this point? Tested tubes? Cleaned controls? It's helpful if you confine all discussion of your TV to one thread, so that people can read about it in context instead of searching around in multiple threads to get a clue about what's happening.

This article has some advice about basic first steps that may be useful:

http://antiqueradio.org/FirstStepsInRestoration.htm

If you have already done all of those good things, then recapping is next on the agenda. The only question is whether you want to do them all at once, or one-by-one (or few-by-few), powering up the TV periodically to see if you're making progress (or at least, not making things worse).

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Fusible resistor ok. Will check B+ and DC on the horiz. cap. I did bring the line voltage up to 117. I do feel silly for not doing a complete voltage check before posting. I'm sorry, my enthusiasm ran away with me.

Not much has been done, other than a good visual inspection and basic cleaning. I am going to jump into the recap, I gotten the list together and will be ordering that Monday. So, soon I will pull the PCB, replace all paper and electrolytics and measure all resistors and replace as needed. I'll test all the tubes, but I don't put that much faith in my cheapie Eico tester. I just got ants in my pants and wanted to see what it did as is. Since I am waiting on caps I'll poke around and check voltages.

Thanks for all the help! I'll try to take a deep breath and be more methodical.

Jonathan

Quite agree. I simply do not believe in powering up any radio or television receiver until ALL of the filter and paper capacitors--"all of them" being the operative-- have been replaced.

Did I mention all of them?? Powering up a receiver with original caps is in my very humble opinion, silky, lazy and risky. Heavy on the risky. Recapping your set fully will reduce risk tremendously. Then you can power it up and go looking for whatever else may be Ailing it, such as mica caps, resistor issues, etc.

It is not all that risky if you do the power up right. A slow start with a variac, the back off so any smoke or signs of trouble can be seen, and periodically feeling the cans and transformer to make sure they are not getting hot is about all that needs to be done to give a safe test power up. (and of course having the sense to pull the plug if signs of trouble manifest)

It is always good to have a baseline before you start changing caps so that if you screw it up you know to check your own work, and not simply blame the set and start chasing shadows.

Second part is true. However, why waste your time with components that everyone knows are kaput, or will soon be!

Just do it right the first time, be careful--don't rush--and more than likely you'll have a nice and SAFE set to tweak on the backend!

George

Anything newer than 1960 I power up replace what (if anything) is preventing it from working right and run it with as many original parts (including caps) as it will run properly with...If an original cap goes in the course of later use I find it change it, and return to using the set. Much of the fun is troubleshooting...Why waste it with a shotgun recap?

If your set is being used properly (with someone watching it at all times) if a lytic goes bad it will be noticeable and unless you let it run in that state for several minutes almost nothing ever gets damaged.

Your claim of fire, and danger rings of trumped up alarmism/over caution to me. I've seen several dozen caps that have gotten hot and puked their guts, but never any cap fire evidence....Hell some sets had problems with the power switches starting REAL house fires when the sets were new and NOBODY here changes a power switch unless it has failed. It's as goofy to me as saying we should gut all our sets and install flat panels cause someone might get hurt from a random CRT implosion. Life is all about calculated risk.

The HV rectifier tube won't get warm with the other tubes. The horizontal circuit and flyback have to be operating for the tube to even work. Normally, you won't even see the filament glowing on the HV rectifier when the set is running.

As an ex-firefighter, for me it is about the risk VS gain equation. Unfortunately I don't know enough in this situation to really asses the risks or mitigate the hazards. So I should be more cautious.

I'm putting together a parts list and I have a couple of questions. Looks like 1 watt metal oxides should fit for the 1/2 watt resistors. How often do these go bad? On a Hallicrafters SX-44 panadapter I did recently, 90% were bad. On an SX-43 they were pretty much all good. What are these Predictas like in that regard? I can order the exact values called for on the video PCB or buy a variety pack of values and see how it goes. Thoughts on that?

I'm not planning on messing with the tuner for starters, just the video board and all the paper and electrolytic caps under the chassis. I can't seem to find a PDF of the Philco manual anywhere. I saw that Phil had a PCB diagram with top and bottom views but mine is different. I'd love to have one of those.

I will keep this project in this thread to make it less confusing.

Thanks!

Jonathan

Edit: Bruce, thanks for the info. That's what I figured, with such a low filament voltage.

Video boards on predictas rarely have issues, no paper caps there, and resistor values are generally not critical. In fact most of the resistors can be off a lot and still be fine.

Generally speaking if you have a lot of exp with diagnostics you can get away with shot gun replacing. If not you are best to base line and then replace a few. Of course with a predicta pulling the PCB is a bit of a pita, but often you can just unstake the grounds and lift a few wires to get access.

I also like to base line a set to determine its overall status before touching it, and that includes cleaning it. I have gotten sets that's that were real dogs due to a single misplaced cap on a botched recap.

I have a series on a 10L chassis, there are several parts. You may find it interesting as I talk about my approach.

https://www.youtube.com/watch?v=PbKmydNJzg0

If you want to jump right to pulling the pcb ck part 5

You can find the Sams folder #439-1 at the early television web site. All the best,Tom

Dave, maybe I am mis-speaking. I mean the main PCB, which does have paper caps. I don't have any tv diagnostics experience at all. That is why I was trying to see what it would do as is, to get a baseline. Considering the PITA to get that PCB off though, shot-gunning might be called for.

Doing some more poking around I see the multi-tap sand resistor is waaaay off. The 8 ohm section reads 30. The 13 ohm section reads 62 and the 17 ohm section is reading 93! Furthermore, I have discovered that R76, the 400 cold, 11 ohm hot, has been replaced with a 10 ohm resistor. Yikes! What is the best modern replacement for that?

Thanks!

Jonathan

EDIT: Tom, thanks but I have the Sam's. It doesn't have the same PCB diagram that Phil had for his set from the Philco manual.

NTC thermistors are still made. Often referred to as "inrush current limiters". Digikey and others sell them.

N2IXK, I'm digging through Mouser and Digikey. Not quite sure, but I am looking for 10 ohms @ 25c? I'm assuming the 25C number has to be at operating temps. All that I see so far seem to have a very high B number, which I assume is the initial cold resistance? As long as the B is higher than 400 all that would mean is a longer start up time?

Thanks!

Jonathan

25C is roughly room temperature, or the "cold" resistance. The hot resistance is usually specified at a given current.

Thanks! Duh, did the conversion wrong. I'll keep digging through data sheets.

Jonathan

The highest I've seen is 220 ohms cold. I used two of them in series: http://www.mouser.com/search/Product...lkeySL12-22101

Bob, thanks! The price is right too. Added 4 of them to the ever growing Mouser order. Also been watching your Holiday resto videos, very helpful and informative.

Dug up some power resistors out of the stash that will work for the multi-tap sand resistor. I'm kinda surprised that the value of that had drifted so high, I've never seen a power resistor drift so much. Are those wirewound?

At work for 48 hours but should have some time to replace the power resistor on Thursday. Didn't get the order in so no new parts bonanza arriving this week. The 21FAP4 will get here this week though. Fingers crossed it arrives intact! And that it will work on a Predicta. We shall see. I was thinking of cutting the CRT wires I need to be able to swap up near the socket and putting bullet connectors on them. That way I can test the 21FAP4 works but continue to use the one the set came with if it has any life.

Thanks all! Really appreciate all the help and advice.

Jonathan

EDIT: I didn't put a link for the bullet connectors, but there is an epay link to actual bullet connectors?

Yes, the tapped resistor is wirewound and I've seen them with increased resistance too. I noticed green corrosion on the leads and think that is the cause.

Interesting. No corrosion visible on mine. Might be internal though. I'll do an autopsy when I pull it out.

Jonathan

Moisture in the air makes those sand resistors corrode. They were never designed to last all these years, even not being used.

Removed the multi-tap power resistor and subbed in some replacements and bingo! We got a raster and a little sound. The picture was dim and the sounds was very low, mostly the occasional scratch. The picture got dimmer after a few minutes of operation. Still, progress! We now know we have something to work with. And it was cool to see the little dot in the center of the screen when we shut it off, haven't seen that in years!

The power resistor had no visible corrosion. I may smash it to see the insides, I am still surprised that it had drifted so far off.

Working on a parts list, digging through my stash to see what I have on hand. The 21FAP4 arrived intact and in the original box with the pin protector. It is supposed to be NOS and it looks like it. Once I get the set working properly we'll give that a test.

Bob, after watching more of your videos, I am leaning towards replacing all the resistors and couplates like you did. What do you thing of replacing the sockets out of hand? After watching the trouble they gave you I am quite tempted to do so.

As to the couplates, I was hoping I could ask you for part numbers for the components. In return, I would take detailed construction pictures and post them in a separate thread for easy location for others in the future.

Thanks for all the help folks!

Jonathan

You may find that the 12FAP4 that you have is perfectly good, and I hope you don't need the spare.

The capacitor replacements should make a big improvement in the image you see on that screen.

Bruce, I hope you are exactly right. While I haven't actually pulled the CRT housing off to verify what I have in there I think it is the original 2V filament, 21EAP4. So while there is still a chance it has life it is a little less likely.

Big ol' cap order on the way, along with some other parts, Novus polishes ect. Not everything I need by a long shot but enough to get to work while I figure out what else we need.

Jonathan

Hi All,

Rio and I got to a little work on the Predicta last night. We got the surge suppressors installed, gutted and stuffed one of the electrolytics and replaced a couple of paper caps. I am starting on the chassis side and will then go to the PCB. That will allow me to get familiar with the set and round up all the parts I will need to do the PCB.

The electrolytic was a nasty mess to take apart! It was hilarious seeing Rio's reaction to it. It was loaded with something that looked like a cross between something you find in an infant's diaper and lithium grease. Came apart pretty easily and went back together and looks good. Rio did a great job of peeling the rim back so we could pull the insides out. Of course, we are checking the resistors as we go along. Of the three resistors I have lifted and tested all three are off, 1k = 1.5k, 220k = 700k!, and a 18k = 15.2k. So, looks like ordering a complete resistor set is called for.

Overall, not a bad start. Should get some more time in over the weekend and get another parts order in on Monday. Fun stuff and good times. Thanks for all the help so far!

Jonathan

Hi All,

Busy week but still managed to get some work done on the Holiday. The bottom of the chassis is almost done. I re-stuffed the two electrolytics that mount on the bottom but used a terminal strip to mount the three to replace the top mount can. The can was too skinny and my caps too big, would have been a job to get it to fit. Since this picture I have done some more work, just on cap to replace and three resistors to check. I plugged it in and ramped it up with the variac and it still works but with the same dim, flashy raster and very little audio.

Next week I hope to pull the PCB and start on that, but it is going to be another busy week. Anyone who has made some couplates want to share their recipe? Bob's videos are very good but I am not quite sure what the best type of ceramic caps to order is.

So far so good! Thanks for all the help.

JOnathan

Only use C0G or NP0 ceramic. Other types drift with temperature. Use mica or plastic film is you can't get C0G in the value you need. I used mostly 630 volt, but a few 500 and 250 where I could get away with it. You should use a 1500 volt or better for the 1500pF cap in the vertical feedback network.

Bob, great and thanks. I'll get some ordered up this week. Drat, I ordered a 1kV cap for the cap (don't remember number, I'm at work) on the board that needs to match the cap on the vertical network. Oh well, I'll order another.

1kv is enough. I didn't have the schematic in front of me earlier.

I made a bunch of extra couplates. If you rather just get them from me, let me know.

Bob, I meant to mention that the odd ceramic tube cap that you thought might be a replacement in one of your videos was in my Holiday too, so it must have been a stock item. Strange kinda cap. Good that 1kV is enough. I'll send you a PM about the couplates.

Are 1n4007 diodes OK to replace the HVDC diodes? I hope so, I already soldered some in. :-)

Also, what value resistor to sub in for the CRT filament for testing purposes. Bob mentions it in one of his videos but I can't seem to find it.

Still chugging along. The container of replaced parts is getting full!

NEVER MIND: Found Bob's video that answered both of those questions, yes and 10 ohm.

1N4007 (rated for 1,000 volts @ 1 A) are fine but I've switched to beefier IN5408 ( 1,000 volts @ 3A) lately. I've heard some guys use two diodes in series for extra protecting in case one shorts. Seems like overkill but wouldn't hurt.

Use ohms law. Resistance = filament voltage / current = (2.35 or 6.3) volts / 0.6 A. Really though you don't need to be exact - something around 3.9 - 15 ohms is fine.

Hey Bob, thanks for the reply. I may order some 5408s, all I have on hand is 5406s. The 4007s will be good enough for testing purposes.

Hi All,

Well, a busy week here but still managed to get a lick in on the Predicta. I got the main PCB removed and started to remove and replace components. I am going with a blanket replacement of paper caps, couplates and resistors. I've come up with a few questions from the components values.

C25: Looks like a little resistor with two black bands. Sam's says it is a 1uF?! I must be reading that wrong, but it would seem that 1pF is the only other interpretation.

R49 and R52: R49 is a 3600 ohm. The notes says this goes with a PCB marked with a yellow dot. R52 is a 2.7mOhm and the notes says this goes with a PCB that has an orange dot. I see no dots on my PCB but I do see a green stripe. I'm guessing I should stick with the values that are in the board, but anyone have any insight?

Over all the board is in decent shape. I have one 7 pin socket that needs replacement. All the 9 pin sockets look OK. In my stash I found some PCB mount 9 pin sockets, one of which is the same make and number but appears a little later. The other ones I have are even cheaper looking than the originals. I'm not sure if I should replace all of them or just the borked one.

Jonathan

Sams says 1.0 mmfd for C25. That's short for micro micro Farad which is the same as pico Farad (pF).

I'd go with the resistor values currently in the board - especially if they look to be originals.

As for the tube sockets, if you stick with the originals be very gentle when inserting and removing tubes. The metal used is fairly thin and breaks easily.

OK, so what kind of cap is the 1pF? I am assuming it's a ceramic and hence no need to replace out of hand. Are these resistor looking caps common?

Thanks Bob! Also, I'm going to take you up on your offer to buy the couplates. I'll send you an email.

Jonathan

Yes, ceramic - no need to mess with it. You will mostly see these caps in tuners and other RF circuits where very small capacitance is needed.