Zenith 25EC58 Restoration Thread - Page 2 - Videokarma.org TV - Video

TinCanAlley · #16 03-26-2026, 08:47 PM

I realized now that I forgot about what I had done years ago to the boost circuit. I replaced the boost rectifier, tested the resistor, but never changed the ceramic capacitor as I couldn't find the correct replacement. Zenith uses a 600pf 2kV and I couldn't find any NOS and for new all I could find were 560pf or 680pf. The same for the HOT. I replaced the damper diode, but not the capacitor for the same reason.

I know Zenith chose that value for a reason, but I don't know how important that exact value is to the circuit. It's the last thing I can think of that might be causing the jailbars.

BeamT · #17 03-26-2026, 09:21 PM

Do you have a picture you can post of a blank raster?

Assuming this is Sams 1370, take a look at C270 10uf 300v on the 240v boost supply from the Horiz Out Transformer. That boost source feeds the RGB Video outputs.

Did I understand correctly the "jail bars" are intermittant?

TinCanAlley · #18 03-27-2026, 09:47 AM

Quote:

Originally Posted by BeamT

Do you have a picture you can post of a blank raster?

Assuming this is Sams 1370, take a look at C270 10uf 300v on the 240v boost supply from the Horiz Out Transformer. That boost source feeds the RGB Video outputs.

Did I understand correctly the "jail bars" are intermittant?

No, they aren't intermittent. They are always there, but can be reduced by bring down brightness and contrast to an unusable level.

Posting a pic from the DVD player screensaver.

I have a new 10uf 300V capacitor on hand as I want to replace them all again to ensure I have the correct replacements installed. I replaced them 13 years ago, but I didn't have the SM, so I ordered solely based on value. This time I used the part numbers from the SM and got all but one based on that info. The other one is supposed to be 25uf 15V non-polar, but the SM has no part number and all I could find was a 22uf in non-polar.

TinCanAlley · #19 03-27-2026, 09:58 AM

I'm attaching a pic of the section with C270. Out of this section, my concern is C258 in the pic (small gold radial). I'm trying to go back in memory as to why I used a Nichicon radial of the type I used for restoring my Pioneer SX-1080. Not sure what that cap does, exactly, but I would assume it is up to the task. Still, I ordered the correct replacement for it as well.

The C270 I left the leads long so I could position it better after the safety capacitor upgrade. Don't know if the longer leads affect anything.

TinCanAlley · #20 03-27-2026, 10:45 AM

This might not look good, but it is possible to parallel four 150pf 2kV capacitors to make the 600pf I need, right? I've found 3 I'd like to replace (flyback, HOT and boost sections). It's impossible to find 600pf and anything close is either higher or lower.

vol.2 · #21 03-27-2026, 01:25 PM

You could, if that's what you have.

Very low value film caps don't tend to come in high voltage variants, but ceramic capacitors do. Some cap types are chosen for a specific purpose, and can't be changed, but that's not always the case. Ceramics, especially very old ceramics, tend to drift in value with temperature a lot, so they aren't used when the value has to be really specific, but newer ceramics of high stability types will do very well at this point, and can be subbed for films in many places. Maybe not a good idea if it's a tuning cap.

There's a very stable Y5R 680pF cap: https://www.digikey.com/en/products/...P6UK5R/2831053

But I can't comment on the specific place in the circuit that your cap is in. Someone else will have to confirm that 680 is okay, and that the small amount of drift isn't a problem.

TinCanAlley · #22 03-27-2026, 04:20 PM

Quote:

Originally Posted by vol.2

You could, if that's what you have.

Very low value film caps don't tend to come in high voltage variants, but ceramic capacitors do. Some cap types are chosen for a specific purpose, and can't be changed, but that's not always the case. Ceramics, especially very old ceramics, tend to drift in value with temperature a lot, so they aren't used when the value has to be really specific, but newer ceramics of high stability types will do very well at this point, and can be subbed for films in many places. Maybe not a good idea if it's a tuning cap.

There's a very stable Y5R 680pF cap: https://www.digikey.com/en/products/...P6UK5R/2831053

But I can't comment on the specific place in the circuit that your cap is in. Someone else will have to confirm that 680 is okay, and that the small amount of drift isn't a problem.

Since they're caps in the flyback and horizontal circuits, I thought they might affect the signal and cause ringing. If they don't serve such a purpose, then I'll leave them be.

TinCanAlley · #23 03-28-2026, 05:43 PM

Found issue with one cap. It's in the wave shape section of the Vertical Output section. The cap in there I tested and it's was at the low end of tolerance (81uf of 100uf), so I decided the new cap would go in. Upon looking up the schematic, I noticed that the cap is in backwards. The schematic shows the positive side connected to the diode and the negative to the resistor. It occupies the same connect points as R292 and one leg of R293. I've attached a pic of how it was and the part of the schematic. In the pic you can see the negative side of the cap connected to the diode.

Am I interpreting the correctly? Even in the SM, the crappy pic of the underside it appears that the positive side is down on the diode side.

I traced the path exactly as the schematic shows. The green/red lead connects to the diode, the other end of the diode connects to both the positive side of the capacitor and 470ohm resistor. The other ends of the capacitor and resistor join up with the lead of the 68ohm resistor and the other end of that resistor meets up with an orange wire that goes to pin 6 of J201. So if the last cap was put in backwards, why didn't it fail or cause issues with the circuit?

BeamT · #24 03-28-2026, 08:13 PM

The picture you posted is not clear enough and is too close-up, so I can't orient what I am seeing. I can't see any of the cap polarity markings, or the diode clearly at all. Test the diode and the resistors.

Assuming the rib on the cap is positive. I believe the cap was in backwards. Should be 100 uf @ 25v. I would go to 35v or 50v for a little more margin. Attached is more of that circuit, which is dynamic convergence and associated wiring, from Zenith CM-122, confirming that SAMS in that area is correct. In the SAMS picture, Cap positive, was oriented to the back of the chassis.

I don't pretend to understand dynamic convergence circuits but you could have impacted several coils and controls on the convergence board/clover. From your prior threads you have been working on that board. Did/do all of the controls work?

Do you have any pictures of the chassis from your prior recap?

vol.2 · #25 03-29-2026, 10:42 AM

Quote:

Originally Posted by TinCanAlley

Am I interpreting the correctly? Even in the SM, the crappy pic of the underside it appears that the positive side is down on the diode side.

Agree with BeamT about the cap.

However, 80% wouldn't generally cause a circuit to fail. It's an indication that it might be on the way out or that it was stressed (possibly from being in backwards), but it wouldn't generally be the actual cause of anything not working.

On the other hand, 80% and high ESR could cause something to fail if the ESR is high enough. You can imagine ESR as adding a resistor in the circuit across the capacitor, which will throw things off by creating voltage dividers and stuff.

Long story short, check ESR if you're troubleshooting. Capacitance is only telling you part of the story.

TinCanAlley · #26 03-29-2026, 04:39 PM

Okay, I managed to find an under chassis pic from when I first got the set, before any work. The cap is definitely installed positive side to the diode. In the second pic, it is after the recap. The recap was done for me by a family member as my soldering skills were pretty non-existent at that time. The cap was put in backwards as the negative stripe side is to the diode. The replacement cap was also quite a bit smaller. The replacement I have, that I just installed per schematics (positive to the diode) is quite a bit larger and near the size of the original. The new cap is the Sprauge part number in the SM.

I have been having issues with doing proper convergence, but the pot that was bad wasn't the one connected to this lead and the other one that I want to replace causes the screen to shimmy during adjustment and sometimes continue to shimmy afterwards. I'll just replace that one and give another cleaning to the rest and see if this reversed cap might be the issue with convergence.

TinCanAlley · #27 03-29-2026, 04:41 PM

Quote:

Originally Posted by BeamT

The picture you posted is not clear enough and is too close-up, so I can't orient what I am seeing. I can't see any of the cap polarity markings, or the diode clearly at all. Test the diode and the resistors.

Assuming the rib on the cap is positive. I believe the cap was in backwards. Should be 100 uf @ 25v. I would go to 35v or 50v for a little more margin. Attached is more of that circuit, which is dynamic convergence and associated wiring, from Zenith CM-122, confirming that SAMS in that area is correct. In the SAMS picture, Cap positive, was oriented to the back of the chassis.

I don't pretend to understand dynamic convergence circuits but you could have impacted several coils and controls on the convergence board/clover. From your prior threads you have been working on that board. Did/do all of the controls work?

Do you have any pictures of the chassis from your prior recap?

Your SM shows what mine does. I've posted two more pics of before and work and after the first recap. I am doing the second recap with part numbers from SM.

I've tested the resistors and they are at correct values. The diode passes 572 one way and infinite the other. So it seems the diode is good.

TinCanAlley · #28 03-29-2026, 04:44 PM

Quote:

Originally Posted by vol.2

Agree with BeamT about the cap.

However, 80% wouldn't generally cause a circuit to fail. It's an indication that it might be on the way out or that it was stressed (possibly from being in backwards), but it wouldn't generally be the actual cause of anything not working.

On the other hand, 80% and high ESR could cause something to fail if the ESR is high enough. You can imagine ESR as adding a resistor in the circuit across the capacitor, which will throw things off by creating voltage dividers and stuff.

Long story short, check ESR if you're troubleshooting. Capacitance is only telling you part of the story.

I have been checking ESR as well as value. The one I removed had an ESR of 540 milliohms with a 100K frequency.

TinCanAlley · #29 03-29-2026, 05:59 PM

Quote:

Originally Posted by BeamT

The picture you posted is not clear enough and is too close-up, so I can't orient what I am seeing. I can't see any of the cap polarity markings, or the diode clearly at all. Test the diode and the resistors.

Assuming the rib on the cap is positive. I believe the cap was in backwards. Should be 100 uf @ 25v. I would go to 35v or 50v for a little more margin. Attached is more of that circuit, which is dynamic convergence and associated wiring, from Zenith CM-122, confirming that SAMS in that area is correct. In the SAMS picture, Cap positive, was oriented to the back of the chassis.

I don't pretend to understand dynamic convergence circuits but you could have impacted several coils and controls on the convergence board/clover. From your prior threads you have been working on that board. Did/do all of the controls work?

Do you have any pictures of the chassis from your prior recap?

Would it be possible for you to post the adjustment section of the CM-122? I want to see if it compares to the Sams, or if it has better/different procedures.

BeamT · #30 03-29-2026, 11:10 PM

Horiz ringing and jail bars in my experience can be very difficult to troubleshoot. Sometimes I've had good luck with a scope, if you want to try that route. The source can be a number of places and can be very subtle. Otherwise I have had some success examining one circuit at a time. I try not to just throw parts at it.

To finish where you left off, I would look at:

C258 10uf 50v B+ Horiz Module (you mentioned above)
C264 47uf 10v Secondary Horiz Drive Transformer

and then work your way through the horiz blanking and then into the video path. This could easily be caused by horiz blanking.

I find it helpful to work with a blank raster, from a known good generator, tuner mid channel, or IF disconnected. Chromatic switch off, color off. This eliminates any outside source issues and gives you a good baseline.

Has this set always had the jail bars? Has the tripler been replaced? Zeno (RIP) always commented on non-Zenith HV triplers causing Jail Bars. I never encountered this but after replacing a separate tripler and focus divider in a 25DC56 with a Zenith combined unit 977-36, I ended up with jail bars. Putting the separate tripler and divider back in, eliminated the jail bars.

What part of the CM-122 Set-up procedures are you looking for? or all of it.

Safety first, the boost circuits is these sets are not only at a higher voltage, they can deliver some current, lots of RF energy.