GE 800D restoration - Videokarma.org TV - Video

bandersen · #1 12-07-2019, 03:25 PM

Stated working on the GE 800D last weekend. It's in excellent condition with no chips or cracks plus all the original knobs including the felts.

Wish it was mine, but I'm restoring it for a client. Two things I noticed right away.

The power cord interlock is flopping around loosely.
The thermal cutout has been crudely replaced with a fuse holder

bandersen · #2 12-07-2019, 03:51 PM

Chassis inside looks very clean. It even has an early ST type 25L6.

It was worked on a little at some point in the distant past though. Several electrolytics have been replaced. Perhaps the same hand that put in the fuse holder.

I was able to find service info in Riders vol4 and a Wallace Teleaide for the 800D version that seem to match.

Sams is the only one that usually includes photos with part locator callouts.

Unfortunately, Sams did not seem to cover this chassis. Sams 78-7 covers the 805, 806, etc. which are very similar but different enough it's not really usable.

That's a shame because while recapping I found one lug with clipped leads on both sides. I have no idea what, if anything, went here ???

All the more frustrating because I had another 800, but sold it a couple years ago and failed to take detailed reference photos.

It's between the vertical integrator caps and horizontal circuits. Any ideas ?

Worse case scenario, I'll mark of everything on the schematic as I identify it in the chassis.

MadMan · #3 12-07-2019, 07:47 PM

Neat little set. I like the half-assed circuit boards with lugs for everything. Idk about the missing component. Early modification, perhaps. I'd imagine it'll work fine without it - whatever 'it' is.

bandersen · #4 01-17-2020, 11:29 AM

Slowly making progress. Have most of the paper caps replaced undernearth and have turned my attention topside.

How the heck are you supposed to get at these caps ?!?
Maybe I'll remove the HV cage.

The screen cleaned up nicely. Figure I better protect that speaker before it gets torn.

vortalexfan · #5 01-27-2020, 07:26 PM

Quote:

Originally Posted by bandersen

Slowly making progress. Have most of the paper caps replaced undernearth and have turned my attention topside.

How the heck are you supposed to get at these caps ?!?
Maybe I'll remove the HV cage.

The screen cleaned up nicely. Figure I better protect that speaker before it gets torn.

The TV you're working on appears to be using the same picture tube as my Philharmonic 8200 Set, which is a 12BP4 Picture tube...

bandersen · #6 01-28-2020, 01:59 PM

It's a 10BP4. Very similar to your 12LP4 just a little smaller.

bandersen · #7 03-18-2021, 09:42 PM

I finally got back to this set over the last week. I ended up pulling the picture tube so I could get at the last few caps. Still tricky but I managed.

I popped in a 5AXP4 test CRT, crossed my fingers and powered it up. Crackle from the speaker, high pitched whine and a faint raster.

B+ was a bit low using a 40 ohm resistor and I was getting quite hot. Dropping it down to 8 ohms got B+ close and the image and sound improved.

Popped in a set of good tubes and the image improved more, but sync is non-existant. Also have the contrast all the way up to get an image and weak sound. Signal at the sync clipper is about 80% low so I'm thinking RF or IF gain is off. Will check resistors next.

bandersen · #8 03-24-2021, 08:32 PM

I found a bad mica coupling cap between the 2nd and 3rd IF stages. The associated plate resistor was cracked and more than 50% low.
Replacing both improved gain and sync stability a bit, but vertical hold is still very difficult to maintain.

I'm also trying to eliminate the bright vertical lines and poor horizontal linearity.

The driver trimmer doesn't seem to do anything and is off center from the chassis hole. It all appears to be original though with the exception of the fuse holder.

I unmounted it and it does test good and is adjustable over the correct range. All the surrounding components test good as well.

I'll bend the mounting bracket, remount and try again. Then get a scope on the HOT grid and make sure the drive signal varies as I adjust the capacitor.

This is proving to be a challenging set to work on.

Electronic M · #9 03-25-2021, 01:01 AM

That cap on the hold control could be a paper disguised as a domino...I generally change all caps of that type 1000pF and up as a precaution.

bandersen · #10 04-06-2021, 07:01 PM

Slowly making progress. Very frustrating set to work on!

Went over the horizontal circuit testing every mica cap and subbing when in doubt. Nothing made any difference.

Vertical hold was improved by replacing the marginal 12AU7 video amp and cleaning the vertical hold control.

Another issue has been the contrast control. I only got an image for about the final 20% of the control.

This control straddles the two B1- and B2- buses and provides grid bias for the tuner RF amp and 1st IF stage. I don't believe this set has AGC.

There is a string of three resistors between those two buses that establish the voltage difference between them. One of them - a 47 ohm - was measuring about 90. Replacing that gave me about 35% action on the contrast control.

It's still finicky, but with patience I can get a stable, watchable image.

That leaves the vertical fold on the left side. I saw a slight bump in the sawtooth wave on the HOT grid, but I think it's more likely some ringing in the yoke or damper somewhere.

This is with a 5AXP4 test CRT so I'm not concerned about the focus or off center image.

bandersen · #11 04-13-2021, 03:38 PM

Nothing I've tried has had any impact on the horizontal fold.
It does appear the flyback is a replacement so that could be an issue. While tracing out the wiring I believe I solved the mystery of the clipped terminals mentined at the start of this project.

The Riders service info mentions two variations on grounding the HV doorknob cap. Mine is currently in the configuration that does not require several components. Those clipped leads are in the general area where I would expect them to go if needed.

The service info also mentions two flybacks used during the production run. One with a laminated core and one ceramic. It appears I have the ceramic (powdered iron) type.

The schematic shows a 470K and a 0.0022 in parallel here while I have two 470K and a 0.001. Seems the damping effect would be the same but not harm in try what's shown.

Tom9589 · #12 04-13-2021, 04:56 PM

What is your damper tube, 25W4 or 25Z6?

bandersen · #13 04-13-2021, 05:06 PM

25w4

bandersen · #14 04-13-2021, 05:35 PM

Worst case scenario I can try swapping in this Stancor A-8130. I'll try ringing the old one to check for shorts. Like to avoid using a NOS spare if possible

Frame looks identical and it has dowels to reinforce the phenolic unlike the cracked one in the set.

Only thing that looks different is the lack of a lug on top for the RC combo.

bandersen · #15 04-16-2021, 10:37 AM

Checked the horizontal output tube grid again and the sawtoothlooks good. The damper cathode waveform is another story. It has a big dip in it. Already tried swapping out the damper tube with no effect. Will continue troubleshooting.