Issue with GE "Portacolor III"
 

This set's been a real thorn in my side, so I posted to the classifieds looking for a set to swap parts with, and it turns out there were actually a lot of sets that used the same chassis, only problem is they are apparently unobtanium. Anyways, my scope is saying I'm not getting any video out of the IF amp ic, (nte1545) but I've replaced it twice, and still no signal. It's got the classic "clean" raster (no snow) symptom of a bad detector, and when I inject composite video into the first video amp, there's no black and white video, just color. I suspect this is because composite is 1v peak to peak and the amp expects 2v. I've ordered another replacement IF amp chip, as the other two were old stock. I'm a little perplexed at this point, as I don't see how two IF amp chips were bad, although they were from the same seller.

Attached is a pic of this section of the schematic. The little numbers scribbled on the chip are voltage readings I took, and you probably can't read them as the file size was reduced, but the only thing of note was that pin 3 was supposed to be .7v, but is 4.5v, and I can't figure out why.

Pin3 would vary with R150 setting AGC. Try cranking on R150.
But I'd re-solder the entire area first.

Resolder all of the griplets first from the top of the PCB. Usually if
griplets are the problem you can rap the chassis and make it come & go.
Beyond that measure voltages & waveforms again. Since you have color & sync you know there is composite inside the IC.

73 Zeno:smoke:
LFOD !

I have actually run a wire through all of the 50 odd griplets that act as vias... I re-soldered every joint in the IF amp area, and there is still basically no signal coming out of pin 5, (if there is, than it's like .005v pp) If I bang and bop the set, or rap on the board, it seems pretty consistent in it's current state. When I turn the agc control (r150) pin 3 actually goes from 5.27v to 5.44v and seems very consistent, just 5 volts high...

Do you know for sure that the tuner is working?

Actually, no. I don't really know how to "test" the output of a tuner, I know it takes RF and turns it into IF, but I don't know how "check" for IF, (I don't have a sweep generator, or a "tuner subber") But I guess that's what "snow" actually is, the output of a tuner without a signal. Maybe the tuner isn't putting out the IF it should be, and so the IF amp chip has nothing to modulate? That being said, I took the IF output from the tuner of a working set that I have and jumpered it to the tuner input of this set, and there's still no video signal. Although, I'm not sure if you can just use another tv as a "tuner subber", as I just used the output and ground of the other tv's tuner.

Having thought about it, I took the output of the broken set's tuner (hooked up to dvd player) and jumpered it to the working set's tuner input, and the signal doesn't look half bad, a little lossy, but alligator clip leads across the bench don't help, so.... I think the tuner works.

I'm almost positive I have one of those sets in my cluttered warehouse.
If it's easy to get to without help, I'll check it out and PM you in a few days.
I'm glad I quit the repair business 30 or so years ago. I don't miss those headaches.

Thanks! Whether you find it or not I appreciate the gesture :yes:

OK first give a detailed description of the symptoms, I think I am
missing something here. Do you have a color picture that goes away to blank white when the color control is turned all the way down ?

AGC When there is no signal or very weak signal both the RF & IF are turned on to full gain. With strong signals gain gets turned down. SO AGC voltages
can vary a lot. Most SS sets the AGC control will go from snow to normal
to a jittery pix as you turn it. Set it to where the snow just goes away..

TUNER Most tuner fails are snowy pix or whited out & wormy. Crude test
is turn the channel. You should see "noise" in the pix & crashing in the
sound. If you do the problem is tuner related. If not its IF related.
Keep in mind sometimes tuners get so dirty they stop working unless you violently shake the knob !

73 Zeno:smoke:
LFOD !

I located it today. I ran it for a few hours. I probably haven't turned it on in several years. When I first tried it back then, I remembered the CRT was a bit tired on the red and blue gun, but after a minute or so, the grey scale doesn't look too bad.
It's a model # 10AB3046W in decent cosmetic shape.
PM me with your phone number, as I'm not that fast on a keyboarder. Phoning is easier. Dave. :thmbsp:

Yes, actually. Only colors, no black and white information at all. If I put on a b/w show, nothing shows up. If I put on something with colors and b/w video, only the colors appear, and only when I crank the color control all the way up. So basically, all I see are highly saturated colors, and everything that should be b/w on the screen isn't even lit. I'm thinking it's because it's not getting the 2v peak to peak video signal it needs at test point 3, as of now it's only getting a 200mv peak to peak signal. Test point 3 comes after the first video amp, but I'm assuming the first video amp (Q200) should already be getting a 2v pp video signal out of pin 12 (I said pin 5 last time by accident) of the IF amp IC.(IC120) Also, contrast control does nothing, which makes sense because it is right on Q215, the fourth video amp.

check your delay line

You may try lifting pin 12 & see if you get 1-2V P-P of video on the
pin. You could also try hooking in composite video at TP 6 from a DVD. Just
be sure to use isolation !
I just dont see having a run of bad ICs but its not impossible.
If it were an expensive power pack then I would suspect bootleg
Chi-Comm crap.

73 Zeno:smoke:
LFOD !

It measures around 60~ ohms or so, with no shorts to the 22v rail.

Just for good measure, I replaced the IF amp IC again, this one was a completely different brand and seller, and it does the same thing. Pulled pin 12 and there was just a flat line all the way down to the 100mv range. The thing is, when I inject a composite video signal straight to the video amp, It basically does the same thing with it's color situation, but I just assumed this was because composite is only 1v pp and the circuit expects 2v pp.

You should have seen something. Its probably not a problem with the IF amp.
Hope you put a socket in there.
Lets back up. Do you have ALL your supply voltages?

140v rail is 142v, pin 3 (155v) is 159v, 22v rail is 24v, 12v rail is 12v, 35v rail is 36v, and I can't think of any others.

Are you able to get sound thru to the speaker?

Yes, very loud static when no station is tuned in, and with a signal tuned in, sound is fairly clear with normal volume.

Have you checked L126, L128, and L145 for continuity?

L126, L128, and L145 all measure good continuity, but I do have some news. I've managed to source a working set with an AA chassis, and when I lift pin 12 of the IF amp IC and measure the waveform from pin 12, I get a 4v pp to 6v pp signal, but when I take the very same IC and put it in my set, (I've installed a socket in my set, though the AA's chassis is already socketed) I get a flat line out of pin 12 with it lifted.

That's great
 

What I would do is put both chassis side by side (make sure everything is connected up) and do comparative ohm-meter checks (with the set off, of course).
I've been thinking you've got an open in the circuit traces some where. Maybe the set took a spill and you've got a hairline crack somewhere.
I've seen that before. Good luck.

So I figured it out... Initially I was trying to figure out why I wasn't getting a signal out of pin 5 of the IF amp IC, so I tried some stuff not really worth mentioning... only to find out that pin 3 of the IC was shorted to ground. C140 in the schematic was responsible for the short, and once replaced I was able obtain a good signal out of pin 5. But, the set's picture still displayed the same issues as previously discussed. So, after some probing I found that I had a good signal out of Q200, but basically no signal out of Q205. I replaced Q205 with no change, checked it, and it checked just fine. I then found that R206 on the schematic, which comes out of the emitter of Q205 and goes through an inductor to ground, was practically open, and had a burn spot. Upon replacing it, the set now behaves like I think it should. So how did the resistor burn up? Well, a while back I was trying to directly inject a video signal into this set, which little did I know doesn't play well with a transformerless set. From what I understood, Q200 went POP when the grounded rca cable tip shot 120v through it, then through chassis ground, then through one of the bridge rectifiers (which also blew) to the hot side of the plug. So prior to posting here, I had replaced Q200, and R202, which was between it and chassis ground. What I didn't know was that it also blew R206, which was between Q205 and chassis ground.

TLDR: I blew it up and didn't replace everything that blew.

Congratulations!
 

I think that set has a bridge rectifier power supply. So its ground is ground to that set only.
Those sets cannot have an external video input for that reason. Modern sets have a switching supply and the transformer in it provides the isolation for external grounded video inputs.
There are video transformers out there but they are kind of pricey ($22).
Those ground loop hum eliminators that are sometimes used by security camera installers do NOT provide ground isolation.
You can verify that with an ohmmeter.
Again congratulations!

Wao. Great sleuthing job! ...Mr. Dragonslayer. :beerchug:

And to think how i used to cuss those with just the intermittent 'griplet' problems.

I still have to get my paypal straightened out.
Evidently you don't need the set anymore. That's alright with me.

I didn't know you were trying to use an external video source with this chassis. You should've used a modulator that converts a video source to VHF channel 3 or 4. They're all over the place for a buck or two.
BTW, I'm a firm believer in GFCI receptacles. It saved a lot of damage to hot chassis sets when contacting the chassis to ground. :thmbsp:

That set could work with video injection if you power it through an isolation transformer.... if in doubt as to wether a chassis is hot always power it through an isolation trans.... especially when plan to connect the set to anything that isn't battery powered.

Oh for sure, how do you think I've been probing it with the scope? Every time I forget to plug it in to the iso transformer, and I hook the probe ground up... BANG! There went another chip :D

If my test equipment has a grounding plug, I always use a 3 to 2 prong adaptor to float the scope. The same thing with my newer TV analyst.
We're only dealing with 120 volts here. If I get between line potential and the equipment, the GFCI will trip.
I'm more concerned about damaging the item I'm working on, than a little tickle.
.

That's a thought... I wonder if it would reduce noise too, if I even turn my soldering station on I get ripple, and I've had to chase noise down on more than a few occasions :boxing:

I've been working on electronic items for slightly more than 60 years and never had a Soldering Station until a year ago. I seldom use it now! :sigh:
I have several sizes of soldering irons and Weller guns. For the small stuff, IC's etc, I use a 23 watt pin point tip. Old habits die hard!