Zenith 25EC58 poor focus

[Carmine]

Hello All,

I'm chasing a poor focus problem on my 1974 Zenith Piedmont (I've redone the speaker cloth on the left, haven't done the right side yet). This will be a daily-watcher in my family room when/if I can get it straightened out.



Here are a few things I know:

The set has some kind of "thermal" issue that gives a raster-only/no-sound until it operates for about 5 minutes, then suddenly the picture/sound will appear. I'd guess this is an IF issue?

The CRT passes all tests with flying colors per my B&K tester. It has plenty of brightness with no bleed/smearing. Colors look good.

The HV safety caps have not been changed. Apparently the part 22-5001 number was not revised during the recall which led to some confusion on my part. I do wish to replace them. My understanding is they are 18 microfarad @ 1600v. Some sources say there should be 5 in the set, but I only find 3... One under the chassis and two on the HV board. I've not found this exact rating, but perhaps I don't know the best source. Any help on that is appreciated. At any rate, the HV appears to be in the normal range.

On to the focus issue... Sharp picture only at very low brightness setting. (As you know, cameraphones make a picture look brighter than it is. This would actually be unwatchable in real life. It also isn't this blue.)



which corresponds to this HV reading



A normal brightness setting gives a blurry picture with some growth in size:



and this HV reading



The schematic (Downloaded from SAMS, complete with hand-drawn correction) says I should see 3.5 KV at the focus pin (I measured on the board)



At the lower brightness level I read about 5KV. Turning it up to the normal brightness level lowers it to about 4.5KV.

Any ideas where to check from here? I'll also mention that turning the screen controls all the way counterclockwise never extinguishes the picture. Even adjusting the brightness limiter never fully dims the picture. I don't know if this is related to the problem.

[Electronic M]

The safety caps are either.018 or ,0018uF....I believe the latter but I don't have the Sam's I read that off of in front of me.

All CCIIs have a focus control. Have you tried adjust it? If it's at one end (I presume you have it set for minimum voltage and best focus) one of the resistors may have drifted.... Often the HV divider resistor (which is often part of the trippler) has drifted...if the special HV five resistor has drifted you can often unhook the end of the focus pot opposite of the end the wiper is on and insert 1-15Meg ohms (it'll take some guess and check work) worth of 2W resistors between the pot and the lead you unhooked from the end of the potto move optimum focus voltage into the middle of the pots range...I try to never add more resistance than the pots max resistance to the string in one go. If the focus gets worse despite adjustment you choose the wrong end of the pot or overshot the value.

I've done this on trippler sets and on the older 12B13C52 hybrid chassis that have the giant ceramic HV divider resistor. With success and it has lasted years.

The video issue I haven't seen in my sets.

[zeno]

1) there was never a recall on the 22-5001.Recall was on the next
chassis style with the 4 lead cap instead of 22-5001's
2) Orange Sprague caps are good. Never seen one open but a few shorted.
White American Radionic brand ones are garbage & usually open.
3) 3.5 KV not enough focus. Should be 4-5 ish KV The 130 V must be stable
or the pix will pulsate.
4) there are at least 3 different HV designs using different
triplers, dividers, bleeders & CRT sockets. Know what you have & save
old parts for there ##,s !
5) early problem usually a cap opens causing too high focus voltage.
Then over time the focus spark gap in the CRT socket gets toasted .
If left alone it will damage other HV parts.
BTW if you like lightning remove the caps & run the set. You get huge arcs,
you wont even get near it

Enuf fer now
73 Zeno
LFOD !

[Carmine]

Originally Posted by Electronic M

The safety caps are either.018 or ,0018uF....I believe the latter but I don't have the Sam's I read that off of in front of me.

All CCIIs have a focus control. Have you tried adjust it? If it's at one end (I presume you have it set for minimum voltage and best focus) one of the resistors may have drifted.... Often the HV divider resistor (which is often part of the trippler) has drifted...if the special HV five resistor has drifted you can often unhook the end of the focus pot opposite of the end the wiper is on and insert 1-15Meg ohms (it'll take some guess and check work) worth...

Thank you for chiming in. I was pretty sure focus was attained in the middle of the pot's travel, so I double checked, and the best setting is almost exactly in the center. BTW, YouTube's magic spy algorithms suddenly suggested this video after I read your post. My set doesn't use a focus divider like this 25DC56, but otherwise appears similar.

https://youtu.be/KsNvdSrLiVA?si=FluMrTq5pE5Vfz83

[Carmine]

Thanks for posting, I was hoping you'd see this since I know you're the early CCII man.

1) there was never a recall on the 22-5001.Recall was on the next
chassis style with the 4 lead cap instead of 22-5001's
2) Orange Sprague caps are good. Never seen one open but a few shorted.
White American Radionic brand ones are garbage & usually open.

These are the three white caps found in my set:




In the video I posted, you can see orange caps on the HV board. This is a "D" series set, presumably a year before mine. At the 20:20 mark in the video he actually talks about the Zenith recall.



So there is a lot of confusing info out there. If one of mine failed open, would I see an affect on focus? Remeber I CAN get it to focus decently, at the center of travel... just not at normal brightness. Per the handwritten SAMS spec, focus voltage is 1-1.5 KV too high now.


3) 3.5 KV not enough focus. Should be 4-5 ish KV The 130 V must be stable
or the pix will pulsate.

Naturally the part of the schematic which I need (and paid to download) is in error. Although the crossed-out part says "5100 ohms" so hopefully no one took that seriously. Should it have said 5100 v? The good news is that if you say I need between 4 & 5 KV, that's exactly where I'm at... Except with acceptable brightness and good focus in different places on the brightness control. No pulse/hum issues. Stable in that respect.

5) early problem usually a cap opens causing too high focus voltage.
Then over time the focus spark gap in the CRT socket gets toasted .
If left alone it will damage other HV parts.
BTW if you like lightning remove the caps & run the set. You get huge arcs,
you wont even get near it

My CRT socket is starting to crumble NEAR the focus pin, but not the focus pin itself. So I'm wondering it that isn't from the instant-on feature? There doesn't seem to be any corrosion on the focus pin. I'm wondering if I should use a non-conductive epoxy or perhaps some dielectric grease to re-insulate the socket.

[BeamT]

Nice TV!!
In my opinion your HV is too high. In the pictures you posted, you have a bright screen and the HV is 28KV. This is a 25KV set. The 25EC58 will have 5 Safety Capacitors, 2 mounted on the Horiz Output Transformer, and 3 located under the chassis, that hold the HV down. You have the 2 on the HOT that are clearly the original white American Radionic capacitors that are known to fail open. On your under chassis picture I see 1 of the original capacitors, and maybe that nearby Orange Drop that could be a replacement. You should be able to see the value on the side of the capacitor. They are all connected in parallel to ground but not mounted in the same location. If you follow the blue wire, try and locate the others. As these capacitors open, or are missing, the HV will rise, if they all open, you get the lightning storm Zeno describes. If you have SAMS 1370-2, you are looking for C265, C266, C267, C268, and C272. I have had good luck with this Panasonic Capacitor as a replacement.
ECW-H16182RJV .0018uf 1.6KV

[BeamT]

Some other thoughts:

Your CRT Socket looks horrible, IMO this set is worth finding a replacement. Pin 11 (Blue Cathode) and pin 12 (Blue Grid) are the ones that look the worst, Pin 9 (Focus) actually looks ok, any greenish residue there? How does the focus pin on the CRT look? Like you found the tie point on the HOT frame is a great place to measure focus. Looks like the original Horiz Out Transistor and HV Trippler, always good to see that. Yes. 4.5-5KV for focus.

Module pins and the Service Switch almost always benefit from a good cleaning.

Best outcome depends on stable and clean 125v, and 24v DC supplies, and the 240v Boost supply. The boost filter capacitor C270 10uf is always a good bet to replace.

I wonder what it was like to deliver and setup one of these back in the day....

[Electronic M]

I'd replace those white caps for sure.

It's possible your screens may be set too high. I'd turn brightness to minimum, flip the service switch, turn all 3 screens down till the line vanishes, turn red up for a just visible line, turn green up for yellow then turn blue up for white, then put service back to normal and adjust brightness for pleasing picture and if necessary adjust color drives for good grayscale.

I have a Setchel Carlson monitor that had a focus issue that drove me nuts till I realized some previous yutz maxed out the screens on a good tube.... turning them down instantly got me good focus.

[zeno]

Agree with Mr. BeamT.
1) the socket is toast & gotta go. If you open it it will be clogged with green rot & a greasy brown mung. Almost any Zenith from the 70's you can use it.
Different part ##'s are just for lead length, plugs , etc.
2) In the front door there is a "Chromatic" switch Must be OFF ( not orange )
for video problem. G-2 controls ( 1.5 meg ? ) were known for bad spots so
watch for that. IIRC you can use from other Zeniths as long as its the same
ohms & has plastic mounting.
3) 3 caps or 5 ? I remember 5 but the C model may have used 3.
What I think happened was some one changed just 2 of them that were
falling apart to the orange ones. What ever the case keep things as OEM as you can.

Zeno

[Carmine]

Originally Posted by BeamT

Nice TV!!
In my opinion your HV is too high. In the pictures you posted, you have a bright screen and the HV is 28KV. This is a 25KV set. The 25EC58 will have 5 Safety Capacitors, 2 mounted on the Horiz Output Transformer, and 3 located under the chassis, that hold the HV down. You have the 2 on the HOT that are clearly the original white American Radionic capacitors that are known to fail open. On your under chassis picture I see 1 of the original capacitors, and maybe that nearby Orange Drop that could be a replacement. You should be able to see the value on the side of the capacitor. They are all connected in parallel to ground but not mounted in the same location. If you follow the blue wire, try and locate the others. As these capacitors open, or are missing, the HV will rise, if they all open, you get the lightning storm Zeno describes. If you have SAMS 1370-2, you are looking for C265, C266, C267, C268, and C272. I have had good luck with this Panasonic Capacitor as a replacement.
ECW-H16182RJV .0018uf 1.6KV

First of all let me thank you... I'm more of an "expert" when it comes to repairing cars. I just retired from a 30 year career in prototyping and testing, so it's incredibly frustrating to me when I see people (usually facebook) telling others to fire the parts cannon, or repeat a bunch of old-wives tales that don't even relate to the problem. That was exactly the kind of FB advice I was getting. When it comes to TVs, I'm sorta-knowledgeable, but not like I am with cars. I'd be the guy swapping ballast resistors rather than diagnosing a lean fuel condition.

With the schematic and your advice, I was able to locate the 3 under-chassis caps. Someone DID replace ONE of the five... Using the correct part, which means they SHOULD have known to do all five.



...and finally I located this



...which hopefully explains my elevated HV and poor focus



Thanks again for the part# on the caps. I just ordered these:



You mentioned delivery and setup. I can tell you that servicing in the home is quite disruptive, although era-correct shag would make it a little easier than the ice-skating rink terrazzo floor I poured this summer!

[zeno]

Hints for servicing an "aircraft carrier" combo.
To deliver / move use a tall appliance dolly with straps. One man can do it.

To work on chassis you can flip out the chassis & put it on a box, leaving the set upright. That brings things out in the open.

Normal consoles you flip on its side & remove 3 of the 4 main chassis bolts
and / or the bottom plate. Chassis will pivot on the last bolt.

In shop we had all wood roll around tables. You would straddle the set on
it & still have room for the box method & small test EQ. After that we had
crash carts with scope, power right, analyst, etc. That was some fun !

BTW enjoy your spaghetti, I switched to linguini but what would you expect. My mother was 100% Irish Catholic & father 100% Yankee & colonial Proddy !

Happy TNXgivings.
Zeno
LFOD !

[BeamT]

It could be the issue with the original Safety Capacitor that was replaced was a short that was tripping the breaker. I would imagine an experienced repair person with a Simpson 260 Multimeter in the day would have ruled out the Horiz Output Transistor in the first 5 minutes, found the low resistance to ground from the collector, eliminated the upper Safety Capacitors, flipped the set over, removed the "Service Saver - Easy Service" plate, and determined which one of the 3 remaining was shorted, and replaced it, in the next 10 minutes. After conscientiously measuring the HV, decided the others were fine.

The capacitors you ordered are a PCB short lead version. Easy enough to remove the old capacitors, leaving as much lead as possible, and
"J hook solder" the new capacitors in place. You could leave the orange drop in place, its probably fine.

While your navy is in dry dock You might consider cleaning the Service Switch, they are often fussy.

You might also consider at least finding the 240v boost filter C270 10uf 300v electrolytic so you know where it is. That supply feeds the RGB Video Outputs and the CRT.

I can't find a part number for the CRT Socket. Maybe someone with an original Zenith CM manual and/or the CRSP can chime in. Those parts often show up on the auction site. As Zeno said, you may be able to find a good sub.

[zeno]

Originally Posted by BeamT

I can't find a part number for the CRT Socket. Maybe someone with an original Zenith CM manual and/or the CRSP can chime in. Those parts often show up on the auction site. As Zeno said, you may be able to find a good sub.

look on part. format is 78-####-##

[Carmine]

After having my capacitor order canceled twice (Elliot Electronics) and EBay seller (Chinese gibberish) can anyone suggest a reputable place to purchase quality .0018uf 1.6KV capacitors for this TV?!

[Electronic M]

Originally Posted by Carmine

After having my capacitor order canceled twice (Elliot Electronics) and EBay seller (Chinese gibberish) can anyone suggest a reputable place to purchase quality .0018uf 1.6KV capacitors for this TV?!

https://www.digikey.com/en/products/...CUApANRAF0BfIA

I only order new caps from digikey or mouser (and on rare occasions some of the antique radio specialty suppliers). They're professional suppliers for companies that build their own electronic products, and they confirm their products aren't counterfeit.

So basically they won't give of the troublesome BS that eBay and Amazon electronic components often do.