Andrea CVL-16 "Tough-Dog"

[bgadow]

The dog-days come in summer, right? Well, I've spent the last month tackling some of my own "tough-dogs", sets that I've worked on before (sometimes multiple times) but eventually gave up. My track record so far is pretty good. I started with my Admiral roundie which had trouble with high cathode current, bad focus & color issues. That one turned out to be little stuff, the trickiest to find being an intermittent with the focus rectifier socket. Next up was my toughest dog of all, a 721ts that I'd been trying to get working for about 10 years. Mostly I found dumb mistakes I made when I shotgunned the recap (a B+ line running to the wrong place, etc) and one little resistor, hidden behind the vert hold pot, that was apparently shorted against something else, thus killing the vertical for all these years I've fooled with it.

Okay, time for this next challenge, an Andrea CVL-16. First, here are some shots of the schematic. I might edit some of them later as I know they aren't the best:

[bgadow]

When they designed this set, they must have been trying to set some sort of record for the number of electrolytics in a TV. They didn't skimp. When I first tackled this set I shotgunned the caps. (I need to start doing just a few at a time-less chance of mistakes). Afterward the set did power up with a raster and audio but then some components started letting out their smoke, notably C5 (an electrolytic with positive to ground, which I wired negative ground like a dope!), C4A (if my notes are right), maybe related to the C5 issue, and R42. As if that isn't enough, something started glowing inside of L30, an IF can in the audio circuit! Okay, one thing at a time...

After some work nothing is smoking. My first issue is, no HV. I really wish I could get my head around electronics theory. Here is what I have going on at the 6CD6 horizonal output:
pin 3 should be 20v but is 2.2
pin 5 should be -26 but is -5.6
pin 8 should be 135 but is 50.
All of the B+ voltages in the set are way high, while the negative low voltage supplies are too low.

I have subbed all tubes in the horiz/hv circuit with NOS, some more than once. The 6CD6 has never shown signs of redplating. There is nothing at the flyback. I have not taken resistance readings. I have a B+K analyst and have tried it to some extent but I'm not sure if it is fully working. I also have a small Sencore sweep circuit troubleshooter which provides a source for horiz osc frequency. It didn't wake anything up. I used that to check the cathode current, which was quite low. I connected an outboard crt subbox in place of the 16GP4 but no luck there, either. So, guys, give me some ideas before I put this back on the shelf for another few years!

[Einar72]

Just curious if you have checked the switch that shorts out the 500 ohm resistor at the 5U4 filament, looks like it raises the B+ in the closed position. Could be making poor contact...

[teevee]

Ok, high B+ and low negative are all related, the set is not drawing enough current.. One good check would be the voltage at the cathode of the damper, (6W4) see if that is conducting. (Boosted B+ source). I'll see if I have the Sams on this set.

[old_coot88]

Originally Posted by teevee

Ok, high B+ and low negative are all related, the set is not drawing enough current.. One good check would be the voltage at the cathode of the damper, (6W4) see if that is conducting. (Boosted B+ source). I'll see if I have the Sams on this set.

YIKES! There's normally 2 to 3 thousand volts of pulse there which will fry your meter. Check for B+ at the plate of the damper first. If OK, then (with the set off) check for continuity from the damper cathode to the H output plate cap. That'll verify if the flyback primary and lin. coil have continuity.

[ctc17]

Sounds like theres no voltage at the plate.
damper issue
open horz lin coil
flyback issue

[ctc17]

4 15 watt light bulbs in series from the HOT plate cap to ground.

[Penthode]

I am still curious: Why shotgun the electrolytics? I have rarely found bad electrolytics which have not been abused. By abused, I mean applying a full working voltage on a cap which has been dorment for the last four or five decades.

I simply go through the electrolytics one-by-one and rebuild the dielectrics over a couple of weeks. I apply a current limited DC supply and let the capacitors re-build over a few days. After a few days, when the full rated voltage of the capacitor is reached, if the current draw is more than about 500uA or if the capacitor is warm to the touch, then it must be discarded/ or rebuilt. Otherwise, it will probably last another 50/60 years. I have a repaired a lot of older sets over the last 40 years and found only a low percentage to be bad. And the failures were due probably to infant mortality rather than age.

Consider this: I wonder how the newer replacements being stuffed into the cans will hold up fifty years from now? The Sprague and Mallory electrolytics were very well built and are generally should remain okay.

Also I try to steer away from shotgunning is always dangerous and a more methodical approach is safer.

[bandersen]

I found the CVL-16 service info in Riders Vol. 6. If interested, I can scan it for you.

I think it's safe to say that many of us have had a different experience with old electrolytics - I know I have. Most have either been completely open and bone dry inside or dead shorted.

[bgadow]

Many thanks, fellas, these are exactly the kind of tips I needed to push me in the right direction. It took me only minutes to find the culprit, though I can't say I'm thrilled: it's the flyback In particular, it is the half of the primary between the horiz lin and the horiz output plate cap. The other half of the primary is fine. I'm afraid that means that this set has now become a big paperweight for the duration. It doesn't look like anyone ever made an aftermarket replacement; it's not in my Thorsardson or Stancor catalogs. The Andrea part number is ST-3036. I looked in the yellow pages for the number of my local Andrea distributor but somehow came up short I have given thought to trying to repair it but I'm not sure I'm up for that adventure.

Again, many thanks for the help!

PS: When I tackle this again, I'll let you know, Banderson. I did notice a few mistakes on this Photofact and was thinking that a factory schematic would be handy. And my experience with old caps is similiar. I figure, why wait for the cap to die, why not fix it while the set is apart on the bench?

PPS: I am trying to avoid the temptation to connect the open winding in series with the second anode of another set, to try and "weld" the break!

[Jeffhs]

Originally Posted by bgadow

I looked in the yellow pages for the number of my local Andrea distributor but somehow came up short

Bryan, I would have been surprised as all get out if you had found an Andrea distributor in your phone book today, in the Baltimore area or elsewhere, as Andrea Radio has been out of business for decades. The company, based in the New York City area (their sets were mainly sold in that region, not unlike Packard Bell on the West Coast), made radios in the 1930s and televisions in the '50s; not sure exactly when they closed for good, but it may have been the late fifties or 1960-'61.

[ctc17]

I bet the break is on the outside where you can fix it. Do a good inspection.

[old_coot88]

Originally Posted by ctc17

I bet the break is on the outside where you can fix it. Do a good inspection.

Ditto to that. Completely dis-mount the fly if necessary to inspect it before declaring it DOA.
BTW, the "welding by arc" method works sometimes on a open element inside a tube, but remember that the weld occurs in a hard vacuum, thus preventing burning. By contrast, arcing across an open xfmr winding will result in a hot flame, exactly what you don't want.

[bgadow]

I'll give it a good try. I can verify the output plate side right down to where it enters the coil but the other side has spaghetti on it and goes down toward the core. I probably would have to label everything very carefully and pull it apart.

[Phil Nelson]

If you can remove the flyback without destroying the leads, it's worth a shot, especially if a replacement isn't readily available.

Phil Nelson