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 Post subject: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Thu 16, 2020 4:49 pm 
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Joined: Jan Thu 16, 2020 4:13 pm
Posts: 9
Hi All,
I'm trying to repair a Zentih SE2564X which has a fully solid state chassis 25EC58 (It's an Avanti Chromacolor II with Space Command).

The unit shows no signs of life with power connected and the circuit breaker reset. I noted that the front panel power switch connects to a PCB mounted to the back of the front panel, so I removed that PCB and checked all the components on it. I found a bad 220uF 50V electrolytic capacitor. I'm waiting on a replacement for that. I suspect that isn't going to be the magical solution to making this work, though.

Does anyone know where there might be a service manual online for this? I can go through every PCB and test every component, but I'm hoping for a more intelligent and efficient approach, like a troubleshooting chart and some schematics, or some good advice.
Thanks in advance for any help or guidance you can provide.


Attachments:
File comment: Chassis in cabinet
zenith-25ec58.jpg
zenith-25ec58.jpg [ 299.17 KiB | Viewed 1657 times ]
File comment: PCB with bad cap
zenith-ctl-pcb.jpg
zenith-ctl-pcb.jpg [ 443.75 KiB | Viewed 1657 times ]
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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Thu 16, 2020 7:31 pm 
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Location: Pewaukee, WI
I probably have the Zenith issued schematic for the main chassis. I might be able to snap pictures of it tonight or scan it at work tomorrow.

Sometimes the front power switch was in series with a remote controlled power relay and both would have to be on for the main chassis to get power... If you can figure out which winding of the power transformer on the main chassis is the 120V primary check for voltage across it. If no voltage trace the wiring from one prong of the plug through the set back out the other and check continuity on every leg of the path. If there is voltage look for secondary voltage and check the VRT can cap.

I may own the same set...I've got either a 25DC56 or EC58 (been a few years since I last opened the back) remote set in an Avanti cabinet with the varactor tuner that lights up a column of numbers on the front...if you get it working and the picture is color on one side and fades to monochrome on the other there is a cap under chassis below the chroma module it is a 100uF 50V gray axial lytic cap... changing that fixed that issue on my set.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Thu 16, 2020 8:03 pm 
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If you have any schematics that would be great! I am working on the same TV as you have - I saw a link you gave to some photos of it on BitBucket a while back when I was researching this morning. It has the column of channel indicators on the front, with each position being able tune any VHF or UHF station. I was hoping (against reason) to avoid taking the main chassis out. It looks like a real project. I saw some suitable test points on top, but didn't know what I should see at them, or what they were relative to - like a single wire labeled '125VAC panel lights'. 125VAC between there and where? Eesh.
Whatever you can provide is much appreciated. I'm trying to save this from being "converted" to having a replacement flat-screen mounted into the cabinet.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Thu 16, 2020 8:54 pm 
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It's possible you can access the under chassis without pulling the chassis. Turn the set onto its side and look for a metal hatch on the bottom (the plastic base may be covering it)... nearly all Zeniths from the early 60s to the last horizontal chassis sets like yours had the hatch. Remove the hatch and you should be able to access everything under the chassis with the chassis still installed.

It was probably over 5 years ago I last serviced mine so I can't remember if I pulled the hatch or the chassis...the chassis on these flat chassis Zeniths (I've had others) are not terribly hard to pull. Take some pictures before you do so you can get the lead dress back exactly.

I'll go fishing for paper tonight.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Fri 17, 2020 12:50 am 
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Here is the crummy cellphone pic edition of the schematic.... let me know if you want it scanned.
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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Fri 17, 2020 1:29 am 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 521
Location: New Hampshire
1) Check the 24 V run supply at the regulator transistor on the main chassis.
You should get apx 24 V on all 3 pins. If all are 0 V service the on/off
circuit. If 24V only on one or two pins service the regulator.

The on/off uses a triac not a relay. It is driven by either a small relay or a photo isolator
on the remote chassis.
Both parts come as kits with a 800-### part number. Change BOTH at the same time.
They show up on Ebay from time to time.
When we got these in for erratic operation we also changed the on/off switch & the remote/manual
switch. They get leaky over time.
Symptoms could be dead set, unstable pix, turns itself on & off, random breaker pop.

73 Zeno 8)
LFOD !


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Fri 17, 2020 3:03 am 
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Does this set have the remote control? If it does then I would think that you could bypass it with a clip lead. If if does not then things get simpler.

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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Fri 17, 2020 3:23 am 
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@Electronic Memory - Thank you so much for these! I'll see what I can get accomplished with these, don't go to the trouble of scanning them. At least I know these exist, and where to find them. Thanks a million.

@zeno - Sounds like good troubleshooting advice. I'll check on those. Are the part numbers Zenith numbers?

@Tom - it had a remote control, the Space Command one. It does not have a remote control. I'm not sure I follow you yet on bypassing the remote. I'll take a closer look to see how the remote circuit might affect the power.

Thank you all for your help. I'll update this with what I find.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Fri 17, 2020 5:03 am 
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If you want I can snap a picture of the original remote for mine so you know exactly what to look for... Zenith invented the ultrasonic TV remote and unlike many companies that used it Zenith remote hand units didn't need batteries. Instead the button cocked a hammer that struck what ammounts to an ultrasonic tuning fork. Magnavox used a bellows and whistle system... almost everyone else used a transistor oscillator and a speaker....


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Fri 17, 2020 4:15 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 521
Location: New Hampshire
OK a little more
The triac kit is 800-618, the isolator is 800-617. I woke up last night & remembered one
number then Google gave me the other ! I new they were consecutive numbers.
The tuner cluster is probably covered by a separate Zenith manual either a tuner manual ( TM-## )
or tuner systems manual ( TS-##). Sams probably has it all. I will check to see if I got it
later today.

73 Zeno 8)
LFOD !


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Sun 19, 2020 3:21 am 
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I found the 800-617 and 800-618 kits on eBay. They were inexpensive so I ordered them.

I am getting < 0.5V on all 3 leads of Q212, which I understand from zeno's post means I am looking for something on the smaller pcb's mounted behind the front panel controls. I had just checked all of the components on one of them for obvious problems, and replaced a bad cap (pic above). Of course I just fanagled that board back in there, and now likely it has to come back out :lol:

I looked at Sams for manuals. There is a Sams item (14670) for the chassis number 25EC58. There is a different Sams number (24910) for the model I have which is SE2564X SC. I assume the manual for the chassis is akin to the pictures Electronic Memory took above. But does it cover only the chassis board? Would those other two be covered under a different manual? Would the manual for the model number (a) include all PCB assemblies, or (b) include practically nothing since every assembly is covered in a different manual? I realize these are questions for Sams, but figured my odds at getting a response would be better here. Thanks all.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Sun 19, 2020 3:30 am 
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You want original Zenith factory service manuals if you can possibly find them, or find copies of them. There will be one for the TV chassis, and as pointed out another one for the tuner assembly which includes the remote functions.

Your trouble is very likely the two parts you have ordered. They were stock items in the service caddy for our road techs back in the day. Can't tell you how many of them we replaced but it was a very common problem.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Sun 19, 2020 3:48 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 521
Location: New Hampshire
The other thing to do is check the safety caps P# 22-5001. If any are white they
MUST be changed. Orange ones are OK IIRC there are 2 on the flyback & 3 under the chassis.

My Sams is missing so I must have sold it. I do have the 25DC56 thats almost identical.
Beware of Sams. Often there is the main manual & separate manuals for tuners,
remotes, stereos etc. Be sure you are getting all folders. Also for $22 sams will sell you a
crappy PDF or Xerox. Find the original paper manuals, they are of very high quality
& will be cheaper !

C U later
Zeno 8)
LFOD !


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Jan Sun 19, 2020 4:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 919
Location: dayton oh usa
does the set degauss when its turned on?
i seem to remember several sets with the degausser hitting on power up but no supply voltages.
it was that bathtub cap next to the power transformer.
to eliminate remote issues jumper blue and black in the 3 pin connector.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Feb Mon 17, 2020 6:39 pm 
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I just wanted to follow up on this - I replaced the parts using the 800-617 and 800-618 repair kits and the set powered on!!! Thanks to everyone for their advice on this. It had a picture for a few minutes, but after it warmed up (maybe?) it got pretty bad. I'm wondering if there aren't some degraded electrolytic caps throughout. I'm going to start going through those. The black bar in the image isn't really there (camera byproduct), this is a menu screen from a DVD+VCR's RF modulator out on channel 4, the best I could get it tuned in. It's disappointing, the picture was pretty good at first.


Attachments:
zenith.jpg
zenith.jpg [ 218.96 KiB | Viewed 1151 times ]
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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Feb Tue 18, 2020 2:34 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 521
Location: New Hampshire
Looks totally out of focus. These can have several different tripler & focus
set ups & sometimes unapproved mods. CRT sockets also went bad.
It all goes back to those caps I mentioned. For now get the markings from the
tripler & HV divider. Also a take a pix from above the HV area.
BTW its just 4 bbolts to loosen the chassis BUT the base may have to come off.
You can work on it but you gotta be careful not to yank any wires off. Put a
heavy cardboard box behind the set & it will hold it.

73 Zeno 8)
LFOD !


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Mar Fri 06, 2020 6:07 pm 
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zeno wrote:
...For now get the markings from the
tripler & HV divider. ...

Not sure what I'm looking for there.
I did finally get replacement caps (delayed in China I suppose). There were two above as you said, but I could only find two on the bottom, not three. BTW, yes you can tip these on their side. It didn't even creak - now that's structural integrity! Here's some pics on it's side, where the caps are, and what I did to replace the bottom ones. I didn't fully understand the existing connection so I just piggybacked on the old leads for the bottom ones.
Attachment:
File comment: Avanti Bottom, caps indicated
Avanti-Bottom-Caps-Indicated.jpg
Avanti-Bottom-Caps-Indicated.jpg [ 547.07 KiB | Viewed 899 times ]
Attachment:
File comment: Avanti Chassis Bottom - Cap Replacement
Zenith-Avanti-Chassis-Bottom-Cap-Replacement.jpg
Zenith-Avanti-Chassis-Bottom-Cap-Replacement.jpg [ 113.36 KiB | Viewed 899 times ]

Here are a couple of high voltage pics
Attachment:
File comment: Avanti HV
Zenith-Avanti-High-Voltage.jpg
Zenith-Avanti-High-Voltage.jpg [ 390.04 KiB | Viewed 899 times ]

Attachment:
File comment: Avanti HV
Zenith-Avanti-HV.jpg
Zenith-Avanti-HV.jpg [ 341.53 KiB | Viewed 899 times ]

One for posterity
Attachment:
File comment: Avanti Rear View
Zenith-Avanti-Rear-View.jpg
Zenith-Avanti-Rear-View.jpg [ 374.37 KiB | Viewed 899 times ]

I've plenty more detailed pics if anyone wants them. Maybe someone in the future could use them.
For now, I'm stuck on this one. The picture looks no better than before replacing the caps :(
Attachment:
File comment: Pic after new caps - lacks color and focus, intensity of white is too high, black not black enough
AfterNewCaps.jpg
AfterNewCaps.jpg [ 193.82 KiB | Viewed 899 times ]


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Mar Fri 06, 2020 7:16 pm 
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See if turning down the G2 controls...If they are set too high they will sag the HV and washout the focus...If that don't fix it measuring the boost, HV and focus voltage is adadvisable. The boost you should be able to measure with a DMM...if the boost is higher than your meter is rated for here is a stealth measurement trick. If your DMM is limited to 600 but the boost is 900V first measure any 350-600B+ rail to chassis and write down the measurement, then measure between that B+ rail and the boost rail and add your last measurement to your current measurement to get the actual boost voltage.

If the boost is low it could indicate a shorted or leaking trippler.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Mar Fri 06, 2020 8:16 pm 
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I don't have a clear schematic, not sure where to measure. The black and white leads to the tripler measure 920vdc, it spiked to 1032ish at power on, then steadily dropped and stayed at 920vdc. Also not sure what the G2 controls are, but I've adjusted everything adjustable I could find (user and non-user) except the pots on the metal panel mounted to the top of the cabinet.
One more observation, in service mode I get a decent horizontal line. The blue arcs high in the center, but lines up on the edges. I assume this is a different thing to fix.later though, first my goal is a better picture.
Update: found the G2 marking :oops: , no change though.


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 Post subject: Re: Looking for help with 25EC58 Chassis - won't power up
PostPosted: Mar Fri 06, 2020 9:33 pm 
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There is one G2 control for each primary color. Sometimes they are labeled screen instead of G2. Most Zeniths they were on the back right of the chassis rear edge (the flyback is above them). If you can't find them trace the 3 white wires with RGB stripes on the neck socket of the CRT down to pots on the chassis.

Correct G2 adjustment procedure (generic for all deltagun color sets) is turn brightness to minimum, flip service switch turn each G2 down till matching color line extinguishes then turn red up till barely visible, then turn green up till line is Yellow, then turn blue up till white on overlap with other w colors. Lastly return service and brightness to normal levels in that order. If a line of any primary color won't show up increase sub brightness control, gun bias control or if those don't exist brightness till that color appears with it's G2 at max, then minimize the G2s and readjust G2 for dim lines as above.

It will be atleast 3 hours before I can take better pictures of the schematic.

The blue bow is a convergence problem, fix it after focus and sweep size and linearity are correct.


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