1970s Zenith Console - Troubleshooting
 

Hello all,

I recently acquired this 1970s Zenith. From what I can gather, the chassis is 25DC56 or 25DC57.

The seller provided video proof of it working prior to being stored in the garage for ~year. There is a slight letterbox burn in on the tube. Hopefully this won't be an issue when playing content.

Currently, I plugged the unit in for the first time and upon turning it on I smelled ozone. It is currently non-responsive. There was no audio present either or else I would suspect the HV circuit.

Does anyone have any experience or item to check on this particular chassis before I begin replacing capacitors in the power supply section?

Congrats on your Avanti. That is the best chassis ever built by anyone.First thing is you MUST MUST check the HV caps. IIRC there are 2 on the flyback
& 3 more under the chassis. They are marked 22-5001 & all the same.
If they are white you MUST change them before anything else. If they
are orange they are OK to leave in. You must use the right type for
replacements or they WILL short out.
After thats done you can trouble shoot it. Its very easy to repair at that point.
To access under chassis there are 2 ways.
1) carefully flip set on its side & remove bottom plate.
2) Remove 4 heavy bolts from bottom of chassis. Place a heavy box behind
the set at chassis height. Loosen wire bundles & flip chassis on its side
on top of the box ( my favorite !).

I loved fixing these but even though we were a major Zenith dealer they
were bullet proof so didnt see many. If it werent for the HV cap problem
they were near 100% reliable for ever. CRT's also as good as you could get.
Never saw a weak one in the olden days.

73 Zeno:smoke:
LFOD !

Hey Zeno,

Thank you! I'm glad to hear it as a good chassis as the looks alone are what made me go after it.

I had a peak and the two caps on the flyback are indeed white with the wording "Special". Do you have a recommended replacement?

And thank you for the disassembly tips! Honestly, with everything being a connection point it looks very easy to get at and service.

As for replacement I think the old 22-5001 caps have been bought up.
I am sure someone will pipe in with the proper replacements. They have to handle the 1 KV spikes on the hoz output plus the 130 VDC.

Reason this is important is the HV runs at 30 KV. Every cap that opens
adds apx 2KV. If all 5 open you are over 40KV HV. I had one where 4 were open & that set sent lightning bolts from from the HV. It will work with a few bad but it will slowly eat up the HV tripler, CRT socket, HV divider when used & Hoz out. The ozone is a sure symptom of trouble.
BTW you may hear about the 4 lead cap. Its the same idea but only on newer chassii.

I managed to pick up 4 NOS Zenith 22-5001 caps on Epay. It looks like that is the last of them. I grabbed a 22-5001 Zenith equivalent by Associates. I figure this will be better than what is current in the system.

As much as I'd enjoy having a Tesla coil, inside of a TV is not where I would want it. Based on the scorch marks I am seeing on the socket and elsewhere, it would seem that your analysis is correct. I'll report back once I get these new caps swapped in.

Thanks again for your help! :thmbsp:

Once in a while the motor run cap that is used to make the voltage regulating power transformer regulate will fail. IIRC when it does the breaker on the chassis will trip. I've had 5 CCIIs and it's never happened to me, but I've seen atleast 3 cases on these forums...So it's something to be aware of.

A point to remember here is that if the socket is scorched, it very well could continue to arc even when the new caps are installed and bring the voltage back down to where it's supposed to be. The scorching produces "Carbon Tracks" which could allow the arc to happen at the lower proper voltage (better conductivity through the burnt carbon VS a virgin socket)

I figure you likely already know this, but in case you didn't, it's worth mentioning......

I will make sure to keep that in mind once I start troubleshooting. I have yet to see an oil capacitor go bad yet.

I had known of it, but didn't consider it. Thank you for the tip. I have attached pictures of what I believe to be from arcing. I am able to scrap it away without issue with my finger so it should clean up nicely. This seems to be a higher hour set, so it could be just use. If it becomes an issue, I may need to source a replacement socket.

If the TV is not showing a picture after it is turned on, but the sound, pilot lights, etc. operate normally, the problem might be in the deflection circuits; however, since you say there is no sound, and the TV is otherwise dead, the problem may well be in the B+ supply, or perhaps a fuse has blown. If the latter, however, make absolutely certain the problem which caused the blown fuse is corrected before replacing the fuse, otherwise the set will just keep blowing fuses.

You mentioned capacitors in the power supply. These could also cause problems with the B+, as I mentioned; if any caps are shorted, they must be replaced immediately, or else the TV will blow fuses left and right. The TV may still work with leaky capacitors, but I would replace those caps immediately before doing anything else. If you see hum bars or other picture distortion, the problem is being caused by 60-Hz hum getting into the deflection circuits; again, the cure is to replace defective filters or shorted tubes in the deflection systems.


If there is a burn mark on the CRT screen, I cannot see it. The burn must be quite small, or else it is located in a corner of the screen where most people would not see it unless they were looking for it, and I zoomed in on the image to have a closer look at the set; I still could not see any evidence of a letterbox burn mark anywhere on the screen. These marks can appear on older TVs' CRTs if the horizontal or vertical sweep is not working properly; when the vertical sweep failed in CRT sets, and the set owner did not turn down the brightness control immediately, the line across the width of the tube could and often did burn a mark in that area--ruining the tube, of course.

Burn marks at the sides of the CRT screen can also occur if a 16:9 image is viewed on an older TV, since the picture will not fill the screen, as was mentioned. This type of screen damage can also occur in flat-screen HDTVs if a 4:3 image is viewed with the zoom control set incorrectly. However, if a 16:9 image is viewed with the zoom set for 4:3 aspect ratio, black bars will appear at either side of the screen; this can and likely will cause permanent burn marks (from the LEDs or backlight) if the picture is either viewed with excessive brightness or for an extended period of time.

I can only imagine how many flat-panel HDTVs were ruined because the set was either not shut off immediately, or the brightness control was not turned down at once when the sweep failed. IMHO, there should be a fail-safe system in HDTVs which will shut down the set immediately if the sweep fails for any reason. Such a protection system, after all, was built into all analog color TVs to guard against X-ray problems, if the horizontal sweep system produced excessive HV or something went wrong with the HV regulator tube or circuitry.

The black looks like static attracted dust from normal use. Rubbing alcohol should clean it, Goof Off will clean what alcohol misses.

I have attached closer pictures of the screen that hopefully provide a better view of the burn-in.


I just went to fire up the TV to verify that it was indeed still dead, but to my surprise it was not. Upon power up the static audio came in, but I did not hear any HV whine kick in. After about 5 seconds, the breaker blew. Resetting the breaker produced the same results. Due to the age of this unit and my desire to daily drive it, it may just be best to fully recap this system (including the safety caps) and begin troubleshooting afterwards. I'll have to pull the chassis out and make a list.

That is good to hear!

Best to recap after you get the HV up

Oil cap. Lift one end & try again. If its bad you will get a raster
but it will pulsate.

Sockets burn inside at focus pin. Almost a Zeniths from the 70's
use the same part but have different lead lengths & connectors.
Dont remember P# but format is 78-####-##.

Cant see the HV area but loosen the tripler & HV divider. Inspect
for cracks, bulging, discoloring etc.

try that
Zeno:smoke:

+1 to what Zeno just said.

Once you get it working one thing I'd absolutely change are all the gray tubular 100uF 50V lytics under chassis. One of my sets had no color on the IIRC right half of the screen because one of those caps leaked electrolyte and rotted a lead off. I think I had another one of those caps fail in something, but don't remember what.

I had restored one of these Avanti sets with a 25DC56 chassis. It had several issues, when I got one fixed, another was found.
The new owner was not a tech, so I had to make sure all the bugs were out.

The 24 volt supply was dead from a burned up 2.2 ohm resistor, so I had HV but no vertical sweep or sound.
It turned out to be a shorted .1 mf 50 volt cap, tubular dark red, that burned up that resistor. You just never know what part is bad until you disconnect everything fed from that source.

Often, 24v feeds thru almost every module, so that if one is removed, the circuit is broken and none get 24v. Generally, small capacitance value electrolytics at low voltages - 10, 50 or 100 volts do not hold up well. I tested EVERY electrolytic capacitor for ESR and found only a few really bad, but I changed all except the large multi section cans, which were good.


Very glad you found those 22-5001 caps! Stay tuned and keep trying, there is lots of Zenith CC experience here.

I’d be weary of that motor cap- unless it explicitly says so, it might contain PCBs. Nasty stuff

Hello all,

Thank you for all of the advice and tips! I have 3 of the 5 22-5001s in. Once I have all 5 and install them I will begin troubleshooting based on your recommendations!

This is going to be a big project, but will be more than worth it in the end.

The main thing is getting the HV up now & a raster. That way
you can be sure the CRT is strong before spending too much $$
on it.
Sounds like the tripler may be bad. Unhook the wire from the flyback
donut to tripler. At the flyback end you should get a nice 3/8 arc
into the air if you put a screwdriver near it. Will also stop tripping
the breaker.

Zeno

Hello all! I apologize for the delay. Got a new job, moved across the country, and now finally have some spare time to put into troubleshooting.

I got the base off and found these items upon inspection. It looks like one the safety capacitors (white) got quite hot at one point.

Also there this blue ferrite disc (choke or inductor?) that is broken in half. I need to get ahold of the schematic to figure out what it is and for.

I am currently working on previously mentioned troubleshooting steps.

Upon lifting the leg of the motor capacitor, I still have the same symptom of audio buzz and then the breaker blowing after a few seconds. There is no filament glow in the tube neck.

Update 1: Upon inspection of the chassis circuit diagram, the blue disc is R324 22 ohm thermistor for the degauss coil.

Update 2: After seeing the 22-5001 scorched on the chassis, I replaced all 3 on the unit with Zenith replacements. Looking at the HV tripler, is this the original unit or is this a replacement unit that combined the focus divider? It is a SCI 7234 "212-139".

Update 3 (closer to the issue): I checked out Q801, 802, 803, and 804 on the Horizontal Output module and they checked out good and within specifications. I replaced the HO module and removed the screws to the Horizontal Output Transistor and the breaker did not blow. The Filament in the neck is glowing. Seems like its either this transistor or the tripler. Will pull the transistor and check it out.

Update 4: I pulled the Horizontal Output transistor Q216 and measured collector to base and collector to emitter for a short. I did not find any.

I reinstalled Q216 and unsoldered the input from the flyback to the tripler. It is still tripping the breaker and there is no high voltage crackle.

According the schematic after Q216 there are multiple capacitor that could have failed and are shorting to ground. I will begin checking these.

Check the damper 103-193 IIRC subs 103-287
That red blob looks like it was the focus diivider got to deal
with that.
If it works with HOT screws out that usually means bad HOT or tripler.
BUT there are huge spikes on the HOT C. May be one of the caps
breaking down but not showing a DC short.

Zeno

Hey Reno,

I'll take a look at that this evening. To be honest, if I can find a tripler that has an internal focus divider I wouldn't mind swapping it out rather than dealing with that orange blob. I remember a forum post listing suitable replacements if I can dig that up.

I hope that something truly failed given the original power on event of a sulfur burning smell; that would make diagnosis much easier.

+1 on Zeno's last reply. In addition to the damper I would also investigate C261 which is just off the collector of the HOT. I'm looking at Sams 1312 and that cap may actually be a "feed thru" It will have a pin on each side of a flange, the flange is grounded, usually soldered to the chassis or a metal bracket. Sams lists this cap as 22-5395 .001 @ 1.2kv

If you are interested, google for a YouTube:
"Troubleshooting the 1973 Zenith 25DC56 Color Television Chassis" by drh4683.
Very good video, methodically troubleshooting the same chassis and circuits you are working with. Breaker popping, he locates a shorted safety cap. There may be a view of C261 in the video. He is also troubleshooting with the Zenith CM manual.

I am working on a 25DC56 and posting in the Solid State sub-forum. I haven't attempted to power my set up yet. I'm waiting on the safety cap subs from Mouser. If any of mine are open, I wouldn't be running it that way for any length of time, and if any of mine are shorted, not going anywhere anyway. So replacing them first is a good initial step, troubleshoot the rest after that.

My tripler, 212-139 is original as is my 63-9012-2 focus divider.

The red blob is your focus divider covered in HV-putty, was a replacement that started to arc. Sams lists 63-9896 as a replacement. I'm not sure about that....

BTW I'm away from my set or I would have checked for C261 and sent a picture.... If it is a "feed thru" it doesn't look like a typical capacitor.

Hey Todd,

That was my first suspect cap. I have actually watched the video you mentioned and picked up a few tips from that. I am also using a Sams and its proven quite handy when identifying chassis components.

C261 is a weird little thing. It is however the last component before my safety cap that got nice and toasty. I'll have to take it out of the circuit and test it.

Should you have any issues getting your safety cap replacements, I have a Zenith 22-5001 OEM replacement and a Associates equivalent left over. (I thought there were 5 safety caps, but I have only seen 3 so far)

I greatly appreciate the help!

It is a feed thru, its located in the bracket that is immediately to the side of the HOT socket. one end is connected to the yellow wire. It looks like a resister with a collar around it.

Not sure how you feel about your past steps but this might be a good time to regroup and repeat and verify some of your work. Zeno's advice is quite sound.

Can you post a picture of the 3 safety caps you replaced?

Have you checked the damper diode?

You can check the feed thru cap with an ohmmeter but that does not rule it out as a problem. It may not be shorted with a DC voltage present but if you put the screws back into the HOT, the horiz circuit will start and the AC voltage there is quite high. From the HOT socket, collector pin, what sort of resistance to ground are you seeing?

NVM, you are correct. I needed to look closer. There are 2, one on the base, the other, you have circled, is the collector.

Usually 2 caps are on the flyback & 3 more under the chassis.
If any got changed to orange ones you may miss them.
Feed thrus are known to go but its rare. I think I had 2 or 3
all on the 13GC10 13" chassis.
I did see a NOS triple at one of the distributors BTW. Try to stay original.
BTW I hope that putty was put on by the owner. If it were a tech
I would fire him. Lucky they didnt see fire trucks !!

Zeno

I will check this this evening and go back through and verify.

I didn't see any other orange ones that looked like my replacements. Looking through the SAMs I only see C268, C267, and C265 listed as 22-5001 capacitors. I replaced the 2 on the flyback and the one right after the HOT. Do you happen to know the designations of the other 2?

I was looking online and had no luck finding a 212-139 tripler for sale. Fingers crossed this one is okay. However, that focus divider is a mess. I do plan on replacing that at least if the tripler turns out okay. This was a one owner set and based on its heavy usage I doubt it was done by the owner.

I went to check HOT collector to ground and sure enough there was continuity. There was also continuity between the HOT collector and emitter. I took the HOT out and rechecked the circuit without it. The collector side of the circuit was no longer grounded.

Long story short my HOT has failed and I was checking continuity for the collector (threads) incorrectly. There is a short from collector to emitter and collector to base. I will be sourcing a replacement.

I have also attached the requested pictures of my 22-5001 caps. They are in for troubleshooting rather than looks at the moment.

Update 1: From a quick glance, the Zenith replacements are all but gone. I was able to find sources for the RCA SK3115, Sylvania ECG165, and NTE165 replacements. Of course OEM is preferred, but is there any pecking order on other brand replacements?

From Zeno the Zenith 212-139 crosses to a 800-791 in the Zenith Replacement line of triplers. I can see the same information. Also crosses to a NTE/ECG 521 if you are willing to stray to a non-Zenith part. In both the 800-791 and the NTE/ECG 521 there is a focus tap that is unused in this application, so you clip the lead and cover it over with silicone.

From everything I can find the original 212-139 was a 6 step tripler, rated at 30KV max, no focus tap. Sams indicates the Focus Divider is 200meg tapped at 40 meg. It appears to me the NTE/ECG 530, Zenith 977-9530, is close. They are also 6 step triplers, rated at 30KV max, with an internal divider, 240meg tapped at 40meg. Sams indicates we should see 25KV at the CRT, and there is no adjustment.

I haven't found any documentation/information this was a recommended replacement for both the tripler and the divider, but I know this was done back in the day.

It would be nice to hear from anyone that has gone down this path. I asked the same question in my thread about a single replacement for both.

Hope this helps, good luck with your set.

Good catch with the HOT. I always had good luck with ECG 165. Be mindful of the insulator and the heatsink compound. The tripler may still be bad, and took out the HOT. You know the the divider has been arcing at some time in the past.....

Due to the state of the focus divider, I am not trusting anything past the HOT.

I didn't realize how hard it is to get a hold of parts for this era of Zenith.
I think I may have to go with a 800-791 tripler and get a hold of a new focus divider. I wasn't able to find the 63-9896, but there is the Zenith 800-616 kit that per the listing is compatible with the 63-9896? I really need to find one of those cross-reference books..

What Sams are you using? I am using the 25DC56 scan from the Sams site and it doesn't appear to mention anything about the focus divider other than it is R361. (not listed in the parts tables)

I picked up 2 HOTs just in case one goes during testing. Is there any specific heatsink compound that is required? I have some used for CPUs; figured that would work just as well.

If you are looking for a Zenith voltage divider, look also at the Sylvania ECG replacement types - the Hi-Div series. An ECG Hi-DIV-3 replaces the 63-9896, 63-9897,63-9898, and the 63-9898-02. Various Mounting positions are possible with the ECG replacements too - unlike the Zenith OEMs.

The Internet archive has the ECG replacement guide from 1989, if you wish to look at the HI-DIV-3 data.

https://archive.org/details/EcgSemic.../n469/mode/1up

I was unable to hunt down any of the ECG Hi-Div-3s. However, I was able to find a Zenith 800-616 kit which replaces the 63-9897 and 63-9898-02. Since the ECG Hi-DIV-3 also replaces those and also the 63-9896, its worth a shot thinking that a 63-9897 will work in place 63-9896.

Not sure if this logic works, but given part availability its worth a shot. I've been trying to find specification information on the 63-9897 to compare to the 63-9896.

The 63-9897 is used in the 19EC13 chassis, and is featured in Tekfax 113, available over on World Radio History to the left on the ET/D (Electronic Technician/Dealer magazine page.

It's shown as R353, Focus Divider on page 152 of the Tekfax (or page 153, as indexed by Adobe Acrobat Reader). Two resistors shown, 200 Megohm and a 40 Megohm in series, tapped at the 40 Megohm.

Same page, in the parts list, R353 is listed as a 63-9897.

Just about all Zeniths back then had the 240Meg focus divider, tapped at 40Meg. Even when incorporated in a tripler (ECG523, ECG529, ECG530) - the focus resistor values stayed the same 200 + 40 Megs, tapped at the junction. The same ECG guide I mentioned earlier has the schematics of the triplers and a description of the HI-DIV focus dividers too. HI-DIV 1 and HI-DIV 3 are identical electrically, but mechanically different for the various chassis mounting consideration......in a pinch, either will do.

Brian
The thing we were trying to do is stay OEM if posable. Reason for that is
in the 80's we had a few with jail bars & a few have shown up here also.
The common thread was new caps, tripler, divider were replaced.
The 800-616 kit did not sub some dividers IIRC the 14 & 16 inch
chassis. Also the kit had the barrier & a plug for the focus. It did
sub any hybrid chassis that had a divider. With some Zenith parts
like CRT sockets, A minor difference got a new part ## but no subs.
Almost all delta sockets were the same for abt 10 yrs. The difference
was plugs & lead length, one could sub them all.

73 Zeno:smoke:

Update: My HOTs and Zenith focus dividers (63-9898-02) came in. I pulled out the old focus divider and it is.. FUBAR. It also looks like it was a 63-9895.

I have a universal Zenith HV Tripler Kit 800-791 coming in the post from Canada sometime next week hopefully.

Would it be unwise to put in the new focus divider and HOT and see if the tripler is okay?

Update 2: I replaced the focus divider with the 63-9898-02 and fitted an RCA SK3115 HOT.

There is life! Sort of. It clearly needs a purity adjustment or a degaussing.

The darker picture is with Chromatic engaged. Brightness and contrast controls are non-operable with Chromatic on. I'm not sure if this is the way it is supposed to work or not. Overall brightness seems a bit low and I am wondering if the HV tripler is slowly dying.

However, the best signal I can get through my RF modulator is.. non syncable. I can make it out a bit and the audio comes through but the picture is skewed and repeating.

There is also a light snap every 10 or so seconds coming from the HV area. Not sure what component is the cause.

The last picture was the closest I could get to a picture and this is only possible with the color turned to minimum.

Good progress! I wouldn't be too concerned with the purity on the picture with the TV on its side. Wait until you are right side up. What signal source are you using? Its doesn't look like you are on channel? If this is an RF modulated source, usually you have a choice to output on Ch 3, or 4, make sure the tuner is the same, and fine tune for to the signal. Make sure you are connected to the VHF input, don't ask how I know. Leave the Chromatic button off for now, and adjust the individual controls for the levels you want. Sorry if this is too basic?

You can obviously see why someone mummified the old focus divider.

From my experience, Triplers seem to work or they don't, except the ones that arc in the mean time.