Zenith Chromacolor console no video
 

Hello guys,

My Mom's early 70's Zenith Chromacolor console is having an issue for the first time since the 80's. Not sure how to find out what model it is. I know she should probably get a new one, but:

1) The old console has sentimental value.
2) She uses it maybe twice a year (for "special occasions") and this is not her main tv.
2) It actually may be more costly to replace rather than fix the Zenith, depending on what's wrong with it (why I'm here for help).

The last time it was on (at least 2 or 3 years ago), all was well. Turned it on the other day and found the audio was fine, but the picture tube was black. No static electron feel when I put my hand on the front of the picture tube so no beam. I removed the back cover and found that there is the orange glow at the back of the picture tube showing the tube is receiving current. I'm hoping that since the end of picture tube is glowing that maybe there could be something else causing the problem.
Does anyone have any info idea what the problem could be and what it would need to be repaired including some thought on cost. Needless to say, if the picture tube is gone, it probably would be cost prohibitive but we'ld like to try to save it. Photos below:

http://i105.photobucket.com/albums/m...ps7faf6ed7.jpg

http://i105.photobucket.com/albums/m...ps84025a8b.jpg

http://i105.photobucket.com/albums/m...ps31e98c37.jpg

Thanks very much.

Lou

no high voltage.check fuses,tripler,hot,etc.this zenith is a keeper and in my opinion,the best set ever manufactured.i have been searching over 10 years for one of these.good luck,keep us informed!

Although not highly valuable, this is maybe the best built color tv that has ever been made. I'm not well-versed in the repair of this chassis, but others on here are. Picture tube is way down the list of things this is likely to be. Probably one bad component in the HV circuit.

Having a schematic would be a big help to you. The first thing to do is make sure that the horizontal output stage is getting B+ voltage. In the newer vertical chassis sets, there is a big 10 watt wirewound resistor that will open and kill the HV. I believe the older flat chassis sets like this one have the same resistor. If there is B+ voltage, check that the horizontal driver module is producing a drive signal and receiving the porper B+ voltage. Also, check the horizontal driver transformer that couples the drive signal from the horizontal driver module to the base of the horizontal output transistor. I have seen these transformers open. If all the above is good, carefully unsolder the lead from the tripler that goes back to the flyback transformer. With this lead moved so it can't arc to the chassis, power up the set and see if you can draw an arc from the lead to a screwdriver. If you get an arc; but, have no HV at the CRT second anode, you have a bad HV tripler. When these triplers fail, they generally either arc/burn or short and blow the fuse/trip the circuit breaker. In some cases, they can fail silently and kill the HV. Be careful in that if the tripler shorts and the TV is left on, the flyback transformer and horizontal output transistor will be ruined. I've seen it happen many times on the vertical chassis sets on once or twice on the sets like what you have.

Thanks for the responses! It's nice to hear that some of us still have respect for the older technologies. I have a friend who repairs electronics but lives some distance away. I will try to get him to help me troubleshoot over the phone based on the recommendations. He actually mentioned the possibility of the high voltage being the issue when we spoke of this recently. I have working knowledge of and know my way around guitar amps but not tv's so I may ask what seem to be simple questions for you guys but complicated for me.
Sampson, is there a step by step anywhere that you know of that could guide me through the evaluation of the components you mentioned?
Radiotvnut,
1) You mention having a schematic would be helpful. Is the schematic that I show in the photo the one to help me diagnose the problem or are their others? The one in the pic I posted is attahced to the inside wall of the tv.
2) Can you point out to me, in the picture I posted, where the components you mentioned are located roughly? Would more photos be helpful?
3) Where would the model# be if I need to find more schematics.
4) Regarding the 10W reistor you mention checking if it's open. Would I be able to see that visually or is it something internal that would need to be measured.
5) You also mentioned if the tripler shorts and the tv is left on that the flyback tranny and HO resistor will be ruined. Did you mean as part of the testing procedure you outlined or now as part of the problem, because we have left it on for a minutes when we were evaluating the problem.
I can clarify further if any of my questions are not clear. Thank you guys again for your help. Your info is invaluable and hope it helps to save this set. Hope you guys can help walk me through this and I will try to confer with my friend to some extent if he's available when I get stuck.

The paper you show is more of a diagram than a schematic. Schematics show how everything is actually wired up together.

those sets were noted for bad service swictches

Well, who is probably one of the last of the great tv repairmen in the Boston area examined the set today using only a long screwdriver and tapping around (it was hard to see where exactly, but definitely on the right side of the chassis as viewed from the back of the set) the chassis and his diagnosis from this was that the flyback transformer and the output trasistor were gone. He said he could attempt to search for the parts (but felt it would be difficult to find these) but instead discouraged us from repairing the set. He felt that even if these were the only components involved (he felt the yoke could also be involved but no way of knowing until the HV is returned and even then, the picture may still not be that great), it still is a 40 year old set that could have something else go at any time. I felt he was honest as he could've easily said to fix it and charge us a fortune.
What do you guys think of all this and do you have any other thoughts? Thank you again in our attempts to decide where to go next with this.

Lou

gone as defective or gone as missing?there are clearly in the pictures.rare to see a flyback bad in these sets.hot yes,but flyback,no.possible though.more like a tripler issue.hope you find the parts and get this one going again.as i said before,the best set ever manufactured.period

I have one of these that developed the same trouble as your set. My trouble turned out to be a bad HOT. There or the tripler is most likely the issue here as a flyback failure is rare in these sets.

The only one of those sets that I've seen with a bad flyback was due to a shorted tripler. When the flyback shorts in these, the circuit breaker will trip within a few seconds of turning it on. The flyback could be bad; or, the technician could have simply told you it was bad. It's not unheard of for technicians to claim that a major part is defective when they really don't want to fix the TV to begin with.

What actually happens is the HV tripler shorts; which, draws too much current through the flyback. As a result, the flyback overheats and shorts; which, shorts out the horizontal output transistor. If you pull the HV input lead from the tripler and replace the HOT, the set will come on and you may get a little HV coming out of the flyback; but, the flyback will become warm to the touch and trip the circuit breaker on the rear of the set.

Good memories of the days when I worked on those. Haven't seen one around here for years.
The yoke is an easy check...a yoke ringer will send test pulses into it, and if the pulse continues to "ring" for a little while the yoke is almost certainly good. I think just about any TV shop that worked on CRT sets has one. I don't remember ever seeing a bad yoke on one of those. I do remember replacing lots of triplers though. I think this set also has a square focus resistor behind the tripler. I replaced a lot of those too, but they usually cracked open and hissed and snapped up a storm.
Did the repairman use a high voltage meter to see what was going to the picture tube?

If you have trouble finding parts, get the Zenith part numbers and post them here. One of us can probably help. I know I have a nice size box of triplers.

this had a separate focus "stick".i remember replacing with a focus block from philco sets in a pinch.also use a 556 tripler to eliminate the stick.radiotvnut is right on the money on this one.that set is worth saving!we will help you get parts.

I'll add that it takes a little more than tapping around on the chassis with a screwdriver to determine if the flyback, HOT, and/or tripler are defective. These parts would have to be disconnected and tested with the proper test equipment to determine if they're good or not. The only good from tapping around with a screwdriver would be to find an intermittent electrical connection on the chassis.

I see the part location diagram shows two different chassis. I remember that 25DC57 was a real dog! It had that troublesome voltage regulator. I don't remember seeing many of that model around. The 25DC56 seemed to be more common and a lot less grief. :yes:

Forget that negative "TV guy" assessment...this IS the best TV made.

Does this set have the black slate on top? I intercepted a trade-in like yours in 1985 and my parents used it as a daily set until 2003 or so, wanting a remote, they got a Sony 27" CRT Wega. It lived in my garage for a while but I parted it out due to the worn-out CRT (only after I rejuvenated it in '85!) and a pile-on of other issues. Had I been on VK then, I'd have kept it but I have the cabinet top yet:D

The low voltage regulator issue in ours was a zener diode but it took me a while to figure that out because it looked like a hum-bad capacitor. The undiagnosed intermittent vertical shrink was probably the service switch:sigh:but I was young then and kept cleaning the module pins and size/lin pots.

If you have a shorted HO Transistor, its easy to tell. Just set your multimeter on "diode test", put black probe on chassis and red on the (121-831) HOT case (the collector), it should read open but if you get the beep, its probably shorted. reversing the leads will read the damper diode, usually OK.

Never saw a fly go on these, but the "22-5001? white critical cap fails - HOT shorts" always the issues I saw. just my 2c

We'll help you fix and keep it. :yes:
Minor, inexpensive repairs will keep yours alive indefinetly!
Like Bryan said, we has parts. just find which one is bad.

You guys are unbelievable. Thank you for the many words of encouragement and offers of assistance. I mentioned it to Mom and she was quite impressed as well and feel she may be on board to give it a shot. She is definitely not wishing to go for a "smart" tv that's for sure. It's not her main tv so she doesn't mind if it takes a while as I know it will due to the learning curve involved for me.
I guess the first things would be to ask if anyone has any idea where to find a schematic, how to check which of the 2 chassis I'd be working with, and what diagnostic equipment I'd need exactly to perform the tests. I may have 1 or two and may be able to obtain the rest, maybe. Thanks for being patient with me on this, guys, and for the continued guidance and assistance.
DavGoodline: Yes, it has the black slate on top!

The guy who looked at your set obviously didn't want to work on it. It would have been nice if he would have just been honest with you and said that, instead of putting on the show he did. I've never learned the fine art of diagnosing electrical problems (other than intermittents) by tapping the circuit with the back end of a screwdriver:no:

I agree with the other posters. If the set had a good picture the last time it was turned on, the likelihood that your CRT has gone bad is pretty low, and you should be able to fix the set. These were great sets, and should last a long time once you fix it. I vote that you give it a shot.

You need to pinpoint the exact model or chassis number. According to the Sams Photofact index, early production chassis 25DC56 is in folder 1312-3, late production 25DC56 is 1375-3 and 25DC57 is 1315-3. I don't have spare copies of any of them but I'm positive somebody on here does. If there is a model number on the back cover that should let us figure out which version you have, if not otherwise marked. It's possible I have a factory service manual for this but that would take some digging.

You are so right, as others have been earlier in the thread, in that he did not want to fix the tv. Looking back it's so easy for me to see that his intent was to come by, give me some mumbo jumbo while waving his "magic" screwdriver wand, and then tell me it needed a flyback tranny, output transister, and the tripler is a part of all this, collect his check for $39.95 for coming out and bidding us a fond thanks for the check, see ya later, bye. He first said he wanted to come out 'cause it's an old Zenith and he wanted to see it. To see if it was possibly something simple but turned out not to be. I should've had my first clue when he arrived and was just opening his repair kit while saying "I must be out of my mind for doing this", therefore setting himself up for the "it'll cost to much to fix" exit.
And so here I am in the forum looking to move forward to, hopefully, a happy ending. Thanks again for the assistance and encouragement as next I will attempt to find the chassis model for the proper schematic.

Yes, it does have the black slate top! What a great piece of furniture if nothing else.

I attempting to study and understand your and others directions for testing as I learn more about the language, numbers, circuit, etc. Still a bit over my head at this point but I'm trying.

I think there's one guy left in the area who claims to make house calls; but, he pretty much does what this guy did. He comes to your house, he plays with the TV for 5-10 minutes, then he tells the customer that the repair will be too extensive to perform in the home and the set must be taken back to the shop for repair. Then, he adds on an additional $50 for the house call.

if this guy was really a repair man with many years experience,he would have told you that this is a fine set.another of the "it isnt worth my valuable services"guys.arrogant and snobbish types.we have a few here in central ohio.have no clue about an older set but will work like mad on a plasma or lcd.all crts are"round tube",never heard of a "hybrid"set,etc.they all say the same thing when you inquire about a roundie or tube set:"why are you wasting your time with that s--t?"because its fun and that was when america built something great.

I have the exact same set. Mine was used just a few years back for 12 hours a day, over several weeks as part of a vintage Christmas display/prop.

(I'd be glad to trade out of it, perhaps for some repair work on other sets)

Either way, they are good sets and your so-called repairman sounds like a tool.

You live and learn. Won't do that again. I have looked around the chassis in various places and cannot seem to find the chassis number stamped anywhere. Was that ever done and, if not, how can I find out which of the 2 chassis I'm dealing with? The only number I did find stamped onthe back of the chassis was 6003419 but I'm guessing it doesn't mean anything. And then, if it's the 56 chassis how will I tell if it's early or late production as bgadow alluded to. Thanks guys.

I'm 99% sure that your set is a 27dc56. Your chassis picture shows no shaded components. It does use the voltage regulating power transformer.
The "D" models are 1973 model year. That's possibly a later probuction set.

Is it safe to assume that none of the shaded components could be on the underside of the board (I haven't looked yet but plan to remove the bottom cover to see what's there)? Which one of these schematics, then, should I be looking for:
"early production chassis 25DC56 is in folder 1312-3, late production 25DC56 is 1375-3" if these would be the only possibilities. Thank you.

All the shaded components should be on top of the chassis. The parts that are mounted under the chassis are marked as such. The late production Sams would include all the latest engineering changes.

Well I tried the Sam's Photofact Index site which had me downloading a huge file, then a zip file which unzipped to a Microsoft Access file, but then Sam's says don't open the file using Access, etc....Needless to say, I got nowhere trying to obtain the schematic. So can anyone tell me how or where to find the schematic for the 25DC56 chassis so I can get started. I didn't think the frustration would start so early. Many thanks again.

To add to the opinions above, you have the best TV ever built. The Zenith 25DC56/57 was one of the last 100% Chicago-built Zeniths, and also one of the last hand-wired by the hands of the women of the Rosie-the-Riveter era.

The FIRST thing that comes to mind, (although this would have to assume that you do indeed have high voltage and you believe you don't), is the Chromatic switch. It's a nightmare when it's dirty, and causes blacked out screen, flickering, color problems, etc. Just to rule that out, maybe turn the set on, and fiddle with the Chromatic button and see if you get anything. If not, then your first thought is probably right; no HV.

If you lost high voltage, it's very easy to troubleshoot, and most everything is available for that set (either new or from other AKers). If that one has a circuit breaker, and it's tripped, you likely have either a bad tripler, or possibly a shorted horizontal output (or both). Remove the 2 screws from the horizontal output (thus disconnecting the collector), and reset the breaker (or change the chemical fuse), and then see if the 130 volt line is live. I think you can find the 130v on the case of the regulator transistor mounted next to the flyback (see the diagram in the cabinet). If the 130 volts is back, then remove the horizontal output and measure it from collector to base and collector to emitter, and see if any direction is short. If so, you likely just have a failed transistor 121-831 (or NTE 165). If the transistor isn't shorted, put it back, and on the tripler, carefully peel off the rubber glob and unsolder the wire coming from the flyback and place the wire safely away from ground, and see if the set turns on, and you should hear a corona hiss from that loose wire. If yes, you have a bad tripler. At that point, I'd update the tripler to an NTE526A, which eliminates the focus divider and double anode wire.

Charles

Post a want ad in the classifieds here with the Sams number & chassis. It might get more views that way. I would be surprised if somebody on here didn't have a copy to send you. It could be scanned but that's a pretty big package. I checked my factory service manuals but didn't have it. If you really can't find the Sams I'll lend you mine, I'm trying to keep my "master" set complete.

That is very cool to know. Was unaware that it was at the tail end of a bygone era. Made in the USA is making a comeback. Look at the Apple Macs soon to be assembled in the US, for ex.

I have tried activating and deactivating that switch (if you mean the one below the on/off switch on the front of the set) several times with no change/effect whatsover.

I am anxious to start the testing but definitely feel I need to study a schematic first to know where all the parts are on the chassis and to know which is which! Thanks for the step by step. There is a circuit breaker on the back of the chassis just below a transformer. How can I tell if it's been tripped? Do I even want to know that at this point? If it was tripped, wouldn't the sound be dead as well?

Can you tell this novice where and what parts exactly on the diagram you're referring to? Thanks.

very easy to diagnose.perhaps you can call one of us and we can walk you through some preliminary steps to help you.kx250rider s instructions were awesome in his post.doesnt get any simpler and precise as that.of course,you can always send the set to me!

Also, be on the lookout for those early white Zenith safety capacitors.
I think in that unit, 4 or 5 are used in parallel. Zenith PN 22-5001, .0018mf @ 1.6KV.

One or two would open(replace all of them) and run havoc in the Horiz. out and HV stages.

Later, Zenith used one cap.(800-860) instead of paralleling .

Glad to help, if I can...

I have the schematic for that set, but not at hand. The paper tag on the inside of the cabinet shows the main transistor locations, but as you point out, it's best to look over the schematic so you have a good idea what you're looking at in the set.

The circuit breaker will make a "click" that you can feel when you press it if is tripped open, but if it wasn't tripped, it will just smoothly press in and spring out again with no click.

If it's tripped, it's almost definitely due to a fault in the set, so to reset it may or may not cause further problems if the fault isn't found first. Honestly I might try it once, but if for instance the tripler is shorted, it could take out the horizontal output on the second zap, etc.

The horizontal output is a large T03 case transistor located near the back of the chassis near the flyback (from behind the TV, toward the corner close to you on the right). The regulator is on the upright aluminum plate just to the left of the flyback. I'd at least pull out the horizontal output and measure it on the diode scale of a DMM (or on the 10K scale if no diode scale), and be sure it doesn't have a short from collector (case) to either emitter or base. No direction should read less than 1.5K, if I recall. I think there is a damper diode built into that transistor, so it will read funny as compared to a regular NPN or PNP, but no shorts.

I'll see if I can dig up the schematic and post a photo, if I get a chance asap, but today/tonight are out due to Valentine's Day plans :smlove:

Charles

Excellent advice, and I noticed at least one or two orange 22-5001s showing in the photo, HOPEFULLY indicating that they were all updated in the 1980s repair. That was a must-do, and Zenith dealers did it free (and also replaced the CRT free if it had been busted by the safety caps opening and sending he HV into orbit). I've seldom if ever seen only a few of them changed, but it's 100% wise to double-check. There should be NO white ceramic tubular caps on the little board beside the flyback, and I think there are two or three safety caps below the chassis near the flyback, which are to be replaced as a set with the ones above.

Charles,

Due to the genorosity, I now have the schematic and chassis layout pages to look at and get started. Thanks for the offer to look and post. Hope I got to you before you went nuts trying to dig it out.
Will I be flipping the set on it's side or top to remove the bottom metal cover plate allowing access to the underside of the chassis for desoldering, etc? I won't have to remove the chassis itself from the set to perform any testing, is that correct? Also, do I have to fear getting zapped by stored cap charges anywhere in the set when working on it in the coming days or weeks (when in unplugged mode, of course)? We have to be very careful when working on guitar amps as the caps often hold very high voltage charges for quite some time after unplugging and must be drained first. Not aware if the tv has the same caveats. I'd hate for the membership to wonder what that glow was off in the distance in the coming days! Not the way I'd like to start the testing process. Thanks.

It turned out to be just 4 pages so that was manageable. Thanks for offering to lend me the Sam's!

:) :thmbsp:

i agree with stratlou!