For a while now, I've had this partially operational Zenith Emperor in my living room. I would really like to get it up and running for the holidays, as I think it would be fun to load some Christmas DVD/CD/Albums and play them through both the TV and the stereo for holiday entertaining.

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/e9ac4cec.jpg

If you recall, the CRT's blue gun dies occasionally (as it is here). It seems to come back if I zap it, but is dead again within a few days. For this reason, I've never bothered to really dial in the convergence or any of the other TV issues. (Sound doesn't tune well with pic, etc.)

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/1a02efe8.jpg

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/cd5faf3d.jpg


When I go it, one of the stereo channels was DOA... In fact, some of the amp output transistors were just plain missing. I brought the amp chassis to Capt' Moody, along with a Magnavox "parts" stereo chassis. I re-installed it and it worked for a few hours over the course of some days. However, one day I turned it on and it immediately "popped" and shut down entirely.

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/26213bb5.jpg

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/c558e0e4.jpg

I just pulled out the chassis again, and there is a 3 amp fuse that blew straight to hell. I am willing to document this thing step-by-step with pictures if others on here are willing to guide me on diagnosis/repair.

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/82dd2b11.jpg

Here are the pros/cons...

Pro:


Better than average electronic knowledge
Fairly good at soldering
Access to some parts
money to buy parts


Con:


No schematic
Have only replaced one capacitor in my life
a zillion other things compete for my time


Can I test capacitors with a VOM for shorts? If your instructions are just to shotgun the whole thing, it will never get done. But I can give meter readings, etc. Can this be done, and where would you start?

What are the chassis numbers of the tuner, amp and tv?

I guess the crt is a given and fairly easy to replace. The hardest part of that is the convergence.

As far as capacitors go I see very few bad ones on zenith sets. I have a feeling the fuse blowing issue is a shorted output transistor or rectifier diode. I have also see situations where something like a diver transistor will randomly short causing one of the output transistors to short. These issues can be tough to troubleshoot.

What are the chassis numbers of the tuner, amp and tv?

I guess the crt is a given and fairly easy to replace. The hardest part of that is the convergence.

As far as capacitors go I see very few bad ones on zenith sets. I have a feeling the fuse blowing issue is a shorted output transistor or rectifier diode. I have also see situations where something like a diver transistor will randomly short causing one of the output transistors to short. These issues can be tough to troubleshoot.

I agree with you about the caps... I have several 40+ year old Zenith sets that fill the screen and are rock-solid with OEM caps. I think it's some kind of dead short too.

As for the stereo chassis numbers, you'll love this... The paper glued inside the cabinet appears to have been damaged for decades, right where the model number should be...

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/eafcc630.jpg

I can only read a partial number that says: **?**5T24-8N24

It's so brittle that if I tried to move the paper, it would simply disintegrate.

nice looking set!i had a zenith roundie that had the same blue gun issue.a gentle tap on the lowest setting would bring it back for a few days at a time.finally got tired and replaced it with a hi-lite crt.not a good swap.looked good in a rca,but wasnt good in the zenith.convergence might hace a coil unwinding on the panel.found this on many zeniths.popping noises sounds like caps.should be an easy fix.great find!

Agreed. Shorted recitifier diode due to excessive ESR from a filter cap probably, or just a filter cap that went south for the winter entirely.
Check those cans!

Check those cans!

How does one do this? Do I measure ohms across some connection looking for 0 resistance (short)?

An ESR meter would help with checking those can cap's...you could of course use an ohmmeter to check for dead shorts like you described...Measure across the can itself or the neg/common lead which are all at the same potential, and each section of the cap *with the set turned off*

on a side note, I always thought it was odd that the tube compliment inside most hybrid SS sets emphasized 'turning power off before removing transistors' ...i mean it isn't such a great idea to pull tubes while it's running either,,,not to mention that they'd be hot as heck.

Get yourself a 100 watt minimum light bulb, if you can get a 150 watt outdoor flood light even better. If you dont have a socket to screw it into solder wires to it. You can cut the plug off a lamp and strip the wires too.
Tie the bulb across the back of the fuse with the fuse out. If you have a short the bulb will light up fairly bright. If working properly the stereo should only light the bulb a tiny bit if at all.
First thing I would do is remove the output transistors and see if the short goes away. If so you can easily test the transistors using the diode check on a multimeter.

I see what look like mismatched output transistors there. I works on high power amps used in nightclubs and its absolutely critical the output transistors are matched, not only the number but the tested gain figure as well. I know its not that critical on low power stuff like this but when I see two totally different looking cans its very suspect. Im really looking at those output transistors.....
Generally its cool to 'stick anything' in there on low power consumer stuff but not always.

Is there a model number on the back of the entire unit?

I don't know about this stereo; but, I've had several '60's era solid state console stereo's that needed a full electrolytic recap in order for them to work properly. Most of the offending caps were the solid black electrolytic caps that were marked "callins", "whale", etc. The short in your stereo could be due to a shorted rectifier diode or a shorted output transistor. If everything is not just right in the output circuit, the output transistor will short again. It may not short instantly; but, it will happen.

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/2a519e9b.jpg

Here is a picture of the underside of the amp chassis. It looks a lot simpler than the typical TV chassis, so maybe this will be good for me to learn on... Perhaps somebody could us a MS Paint or Photoshop program to show me where to test for a shorted diode, or shorted cap?

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/e15c86c0.jpg

Picture of the top-side.

Tie the bulb across the back of the fuse with the fuse out. If you have a short the bulb will light up fairly bright. If working properly the stereo should only light the bulb a tiny bit if at all.

Not quite sure what you mean by this. I should solder the connection across the fuse, effectively using the 100 watt bulb parallel to the fuse? This will also require a new (unblown) fuse, right?



First thing I would do is remove the output transistors and see if the short goes away. If so you can easily test the transistors using the diode check on a multimeter.

I get this part. I will do this first because the connections are very easy to get to.. I don't even need to remove them from the sockets.



Is there a model number on the back of the entire unit?

According to the brochures that Doug posted a while back, this is model X8580H in 1967. The TV is Chassis number 25MC46Z, if that helps date this as a 1967?

Page 19 on this PDF link:

http://www.mediafire.com/?nwqgjoeymtz

Leave the fuse removed using the light bulb AS the fuse. That way the bulb tells you the level of short and you dont blow fuses over and over testing.

The output transistors that drive the speakers are on the heatsinks. The big ones below look like the drives and the small little plug in ones are predrivers.

This uses driver transformers between the driver and output, so it makes it fairly tough for a problem in the driver or before circuit to fry the outputs. If it turns out the drivers are shorted, it could very well be a leaky cap if caps are used to isolate the output transistors from the speakers.

Start by pulling the big transistors out one at a time, measure between the two pins then between the case and each pin using the lowest ohm scale setting. If one is shorted it will read close to 0 ohms.

The other way is the check it with diode test on the meter. A reading of .500 volts is common in some directions but none should read 0 or shorted.

Do I see 8N124.. ? that would probably be the chassis number.

Check the two rect to see if their shorted, then check all the ebc on all the sockets to see if there is an shorts, OR remove the transistors and check them above. The main rectifiers are the ones studded into the chassis with the blue wires. I also think i see a small one. You may need to unbolt the stud and lift the rectifier out of the chassis. I bet that chassis is positive, thats why all the caps are isolated.

Looks like one of the driver transformers has been replaced and in that case it was most likely smoked if a driver shorted in the paste.

http://justsmog.com/Clay/2a519e9b2.jpg

Do I see 8N124.. ? that would probably be the chassis number.

Check the two rect to see if their shorted, then check all the ebc on all the sockets to see if there is an shorts, OR remove the transistors and check them above. The main rectifiers are the ones studded into the chassis with the blue wires. I also think i see a small one. You may need to unbolt the stud and lift the rectifier out of the chassis. I bet that chassis is positive, thats why all the caps are isolated.

Looks like one of the driver transformers has been replaced and in that case it was most likely smoked if a driver shorted in the paste.



It's 8NT24, so jives with what's legible on the pasted layout.

Thank you for pointing out the rectifiers. I thought they would be those square heat-sink looking things I've seen in TV chassis. When you want me to check for a short, in what two places should my multimeter probes be? One on the soldered connection, one on the chassis? Or should I unbolt them?

On the driver transformers, all four of the rivets appear to be original, no signs of them having been removed, no scratches on the chassis, etc.

I did check the E & B terminals with my meter set on diode. All four outputs had similar readings, .005 in both directions (polarity). The two big drives had different readings based on polarity of E & B, .115 and .490, but were similar to each other... Maybe .117 and .450

I'll try the light bulb thing in a while.

You are going to have to remove the transistors to check them. The .005 from e b is most likely measuring the driver transformer.

Try checking the rectifiers in circuit. One meter lead to chassis and the other to blue wire one then blue wire two. Then flip the meter wires. Should measure around .450 on one and open (what the meter displays without the leads touching anything) in the other direction. If it measures something and slowly moves to open that just the caps taking a charge.

NM on the driver transformers, one just looks new or different. It could just be the flash reflecting off the wax in the paper.

Here's what happens... Both of the rectifiers start out with a high reading, sometimes as high as the .450 you mention, then it quickly goes back to .002-3 or so. Doesn't matter which polarity I use.

:confused:

That sounds backwards but not shorted. Pull the transistors and test them.

That sounds backwards but not shorted. Pull the transistors and test them.

Using the diode scale, here are the transistor readings once removed (green/blue = alternate polarity):

http://img.photobucket.com/albums/v619/Chromacolor2/TVs/229c474d.jpg

Note that I did not measure the pre-drivers because they have three legs and I was unsure how to measure them.

All of them have 3 legs, the 3rd leg on the big ones is the case. Let me see if i can make you a quick video on how to test them.

All of them have 3 legs, the 3rd leg on the big ones is the case. Let me see if i can make you a quick video on how to test them.

I think I figured out which leg was the case.. The one that doesn't sit directly across from another... Sort of the odd-man-out, or top of an isosceles triangle?

If so, I measured them and came up with the following two readings. I had to move the meter from Diode to 2K ohms before they had a reading. Both read higher, and quickly ticked down to these more stable numbers.

1.716, infinity & 1.650, infinity.

here you go. http://www.youtube.com/watch?v=REW2lF0sb74

painting all day, be back later. Germanium transistors may show some leakage but no shorts

---

Latest update:

I went to my local electronics supplier (http://abelelectronics.com/) (not a chain store, I wonder how long that website has been "coming soon"?) and they looked at my original fuse as if it were from another dimension... In other words not only didn't they have it, they had never seen another like it, and these guys don't sell mobile phones and X-boxes. It was an odd fuse, having small tabs that lock it into place.

Although I hate modifying things from original, rather than hunt for an unobtainium 3.5 amp fuse, I soldered in a 4 amp circuit breaker that fit as if the chassis had been designed for that all along. :thmbsp:

Then I put everything back together, but only used one screw in each transistor... Figuring that I'd be removing them one at a time to find a bad one. I fired it up, but soon realized the second screw must secure the third leg (ground?) of the transistor. I came right on, but only from the left channel and the bass sounded like garbage even at low volume. I let it run like this for a few minutes, then shut it off and felt each capacitor can. They were actually cold. (This is Michigan in November after all.)

So I powered down and added the missing screws. Volume was set all the way down, but as soon as I powered on, the loud hum of death came from the speakers. I immediately shut it down, and saw just a wisp of smoke from the chassis. It might not have been on long enough to even trip the .5 amp larger breaker.

Couldn't feel anything warm, and a "sniff" test only revealed a slight smell around the upper transformer (as seen in the under chassis pictures). I suppose my next step might be to pull all of the power transistors and keep adding them until something bad happens again, or test them out of circuit as was suggested by CTC17 and Andy.

Have to do a few other things before I fool with it again tonight, but in the meantime your thoughts are always welcome. :yes:

If I have a bad transistor, I can't determine B vs. E if E is shorted, correct?

Therefore, going by the B & E markings on the transistor socket, my output transistors would look like this:

B E


c

When I check two of the matched transistors, I have continuity between E & C in both directions, in other words, shorted. On the other two transistors, I have "some" resistance between E & C, but definitely not infinite.

This would indicate all four output transistors are shorted?! Could some massive failure have taken out all four?

Did you watch my video on how to check the transistors?

The circuit breaker is a BAD idea. Its response time is much much to slow. Where a fuse will blow in quarter of a second the circuit breaker will hold on for several seconds and cause more and more damage,
Get that out of there and put a regular fuse holder and AGC style fuse in, and if a 3.5 amp is not available go with a 3 amp.

Ohh, dont forget the light bulb trick I told you. That will save you a major headache.

Yes on the transistor case. On diode check you should get no reading from C to E, it should be open. Emitter, Base, Collector. Non of them are grounded.

If it were me I would replace all the electrolytic capacitors first...this process has never let me down....also new rectifier diodes would be a good idea too.

On jukebox amps when I had indication of a short, first I would replace all caps and remove the output transistors, then power up the unit with the test lamp in place of the fuse. If the lamp is dim the problem is in the outputs. Don't remove the test lamp until you have fixed the problem. The lamp will allow enough current through to allow the amp to work once you clear the short but will light up and prevent further damage if the short recurs during testing.

Also I would not test it on the speakers in the console if possible...have seen cases where shorts in output transistors or caps destroyed speakers by putting DC into them.

And make sure the insulation is right such as mica wafers between the output transistor case and heat sink when re-installing them.

Did you watch my video on how to check the transistors?

Yes, thank you for posting it. As I said, I am seeing some amount of continuity between C & E, in both directions... Even if I have mis-identified E vs. B, I should not be seeing any continuity with C in both directions, correct?



The circuit breaker is a BAD idea. Its response time is much much to slow. Where a fuse will blow in quarter of a second the circuit breaker will hold on for several seconds and cause more and more damage,
Get that out of there and put a regular fuse holder and AGC style fuse in, and if a 3.5 amp is not available go with a 3 amp.

Ohh, dont forget the light bulb trick I told you. That will save you a major headache.

Yes on the transistor case. On diode check you should get no reading from C to E, it should be open. Emitter, Base, Collector. Non of them are grounded.

Noted. I'll change it out and try the light bulb.

As I mentioned, I haven't the time nor inclination to shotgun all the caps in this thing. I don't think I learn anything that way, and it's not all that "fun". If that's the best we can do for diagnosis, this console will probably just end up on a curb.

If the transistor is not shorted you can easily identify the Base using this method. I will be the pin that gives you .2 -.5 volts between it and the other two leads. Say if you hold the black lead on B and move red from E to C and get .450 on bot E and C you know the black lead is on B. Now if you reverse red and black it should read open.