Zenith - One color on startup?

[bogart219]

Re: Zenith - One color on startup?

Shoot, I was examining the board on the right

And found two more leaking caps.

When I pulled the bigger one out, these black pieces of film came off on my fingers. So now I don't know what value it is to replace. Its listed as CX3452.
How can I find this info without buying a service manual? The small one next to it was a 47uf @ 35v. Am I screwed? It looks like this:

The main sticker on the tube said zenith but their was another sticker that said
"T.Akamatsu" If that means anything. Thanks again!

[Wizard]

Re: Zenith - One color on startup?

What's the model of this TV again? Then someone will tell u what voltage is on this power supply.

Cheers, Wizard

[bogart219]

Re: Zenith - One color on startup?

Model #SL3285BG

[kc8adu]

Re: Zenith - One color on startup?

then its certainly not the crt.

[Wizard]

Re: Zenith - One color on startup?

yeah i know but I was suggesting to have big resistors on the CRT board resoldered but get these resistor pulled out and scraped clean. I have to do this on RCA and Zenith and sone other models. Because the way they clean the circuit boards with corroded the leads in a way it wouldn't take solder after awhile.

Cheers, Wizard

[bogart219]

Re: Zenith - One color on startup?

I fuxed it up. For some reason I tried to take the crt board off to examine on my work bench. I got everything discconnected except for one red wire going to the flyback trans. It went behind a plastic housing that held the focus & G2 or something buttons. IT look like the cover was held in place by 4 clips. There is a little board in there. The two adjustment knobs,(focus & g2) have wipers that make contact with that board. I cracked the board in half. Whats a sin is I didn't have to even mess with that part. I did find bad solder joints and bad cap on the crt board. I replaced those bad caps in the picture above. For the one I didn't know the value. I substituted one around the same size, actually a little bigger. 470ohm @35v. I put everything back together. I get sound but no raster at all. No high voltage. I'm an asshole. Hope I didn't offend anyone

[Wizard]

Re: Zenith - One color on startup?

Oooowww. No need to pop off the cover for focus/screen box. And no need to disconnect wires, just the necessary wires plugs to disconnect to get chassis freed enough to flip over to see.

Time for another focus/screen assembly. Try to search around, see if you can get a spare similar zenith part and transfer the ceramic board over to yours. Bit tricky to heat solder to get wire off the board. Or find a RCA CTC169 chassis and take the focus/screen assembly (snapped onto the flyback and is seperate) and hang it on somewhere else and route wire from flyback transformer (few KV on that) to this.

Cheers, Wizard

[bogart219]

Re: Zenith - One color on startup?

Wiz,
How do you guys usually dispose of 150 lb. tv's?

[bogart219]

Re: Zenith - One color on startup?

PS: If one of you guys could call me an asshole, it would make me feel a little better

[PlainBill]

Re: Zenith - One color on startup?

PS: If one of you guys could call me an asshole, it would make me feel a little better

Why would we do that? Yes, you made a mistake. Hell, you screwed up! It happens.

When my sons were younger the next door neighbor would babysit them. This lady was perhaps 10 pounds overweight, and looked like the single (divorced) mother of 4 kids. One day she went to the beauty parlor and had her hair done. When she came home her kids asked her live-in boyfriend "Don't you think mom looks beautiful?" His response "I won't tell her she looks beautiful until ALL of her is beautiful". Now HE was an asshole.

My favorite 'screw up' story is from the late 1970's and involves a 12" black and white TV. The owner - one of the guys I worked with - tried to fix it. When he didn't get anywhere he asked me to step in. He even supplied the Sams Photofact.

The problem was simple - no horizontal oscillator / sweep / high voltage. The horizontal tube (combination oscillator and output) tested fine on a tube tester, so I started looking at voltages. The easy way to work on this was to put it upside down on a stand so I could probe the pc board. B+ was fine, but there was no plate voltage at the oscillator.

Working my way through it I could easily see where resistors had been pulled, then replaced (crudely). Finally I hit a spot where the schematic said it should be 50 volts, but it was zero. Pull the plug, wait for the caps to discharge, and measure the resistor feeding the circuit - the schematic said it should be a 2.2K resistor, I read over 100K. I turn around to my parts bin to grab a 2.2K resistor, intending to solder it across the open one. I turn back just in time to see the TV roll over onto it's face, then land on it's back on the floor.

Of course, the neck of the picture tube was broken. I wound up buying the guy another TV.

PlainBill

[Wizard]

Re: Zenith - One color on startup?

I can second that, Broke the pip by pushing back too firmly, circuit board pushed the CRT board sideways (instantly voiding the vacuum with a quick whoosh), on a customer perfectly good amber monochrome monitor and I had to take my best mono monitor and swap tube in. Sigh.

It was TTX model TTL 12" mono amber monitor with sharpest text. By then I had moved on to color VGA little later.

That was long ago. That action was not all bad, strengthened the trust and wonderful friendship with now then owner of the computer shop for years to come. Closed his computer shop last year as computer finally got commundity status and cheap then. He planned to run his business for 7 years and predicted that which turned into 18 years.

You can do it with an subsititute from a RCA using CTC169 chassis's focus/screen assembly that is seperatable from flyback transformer.

Cheers, Wizard

[bogart219]

Re: Zenith - One color on startup?

Thanks for the kind word fellows. I guess if that is the worst screw up I make,
I will be lucky

[Krankshaft]

Re: Zenith - One color on startup?

I was removing a signal board from a RPTV once and forgot to remove a corner screw securing it to the plastic chassis.

When the board didn't want to come out I became impatient and pulled harder. SNAP!!!

Luckily it was a 2 layer PCB super glue a razor knife and some jumper wire fixed it.

Focus / Screen resistive divider you mean those components aren't integrated into the flyback?

You sure you can't find an external tripler on there too ?

[Wizard]

Re: Zenith - One color on startup?

Triplers are really OLD era. Way goes back when flyback transformers was early design and tripler/diodes wasn't as good and failing often, hence seperate unit. The tripler is now built into the flyback transformer as series of diodes for every number of turns of windings. First turns and first diode is where supply is tapped from for the focus/screen power source.

CTC130 to CTC169 chassis all used external focus/screen assembly. I can send you one if you wish.

Cheers, Wizard

[bogart219]

Re: Zenith - One color on startup?

There was a half bridge diode chip near the main power in that one of its pin looked burnt so I touched up the solder on it. It has 120 ac going in to it and about 170 dc coming out. Does this make sense? How did the voltage increase.
I got no high voltage at all. Maybe there is more wrong than just the flyback trans. When I take my meter and go from the negative side of that bridge mentioned above to each terminal of the flyback, I only get about 50 volts dc. What kind of voltage should be at the crt board? Thanks!

[PlainBill]

Re: Zenith - One color on startup?

There was a half bridge diode chip near the main power in that one of its pin looked burnt so I touched up the solder on it. It has 120 ac going in to it and about 170 dc coming out. Does this make sense? How did the voltage increase.

AC voltage measurements are the RMS (root mean square) value. In essence 120 VAC does the equivalent work of 120 VDC. But the PEAK value of AC is 1.414 times as great as it's RMS value. And it's peak value is important when AC is rectified. See Wikipedia.

I got no high voltage at all. Maybe there is more wrong than just the flyback trans. When I take my meter and go from the negative side of that bridge mentioned above to each terminal of the flyback, I only get about 50 volts dc. What kind of voltage should be at the crt board? Thanks!

Do you have a schematic? Most TV sets built within the past 30 years use some form of a scan derived power supply. While it is possible for an experienced tech like Wizard to do an effective job of troubleshooting TVs without a schematic, others find it to challenging.

PlainBill

[bogart219]

Re: Zenith - One color on startup?

No bill I don't have a schematic. Yes it is very challenging. One thing I didn't mentioned that I probably should of pointed out before when I said I don't have any high voltage was that I believe I don't have any filament voltage, ie I don't see any small light at the neck of the tube that I have seen in the past. Is the voltage feeding that crt board on the neck of the tube getting its voltage from the flyback transformer also? Wouldn't I need filament voltage first before I could get HV? Thanks!

[PlainBill]

Re: Zenith - One color on startup?

No bill I don't have a schematic. Yes it is very challenging. One thing I didn't mentioned that I probably should of pointed out before when I said I don't have any high voltage was that I believe I don't have any filament voltage, ie I don't see any small light at the neck of the tube that I have seen in the past. Is the voltage feeding that crt board on the neck of the tube getting its voltage from the flyback transformer also? Wouldn't I need filament voltage first before I could get HV? Thanks!

I don't have any experience with mid 1990's Zenith TVs, but I would expect the heater supply for the CRT was either supplied by an independent winding on the power transformer, or came from a winding on the horizontal output transformer. In either case, filament voltage should not be a prerequisite for high voltage.

I tried searching for a schematic for that set, but came up blank. I wonder if it would not be more effective to search by the chassis number.

PlainBill

[Krankshaft]

Re: Zenith - One color on startup?

If you're not getting heater voltage and it's supplied by the flyback (I have never seen a TV that didn't but I mostly work on 95 and newer sets) then either the heater winding is shorted. Or more likely the horizontal circuits aren't functioning.

To check for anode voltage (to see if the flybacks working) without a HV probe power the set up and place your arm about 1/2" inch from the screen if you feel your hairs raise you have HV.

The high frequency whine the flyback makes is very apparant to me as well but I've heard some people can't hear it.

The heater voltage is supplied by the flyback and so is the 30K anode acceleration voltage. The flyback is driven by the HOT no horizontal drive waveform from the deflection IC = no horizontal deflection and no power output from the transformer.

In any case since I heard you broke the screen / focus block most likely that is triggering protection so that the set won't come on anymore.

[Krankshaft]

Re: Zenith - One color on startup?

As for the voltage readings to the flyback from the collector of the hot you should get around 130 volts or so. The horizontal B+ value varies slightly from set to set and some sets even have a POT to adjust this voltage.

This regulated voltage is usually supplied by either a linear regulator (heatsink of this component is unisolated don't touch it while the set is running) or the main switching supply.