Motorola 7-VT2 worth restoring ?

[bandersen]

I recently picked up an Eico 944 flyback and yoke tester so I can finally check the donated flyback. It's good!

Gave myself a little shock too

[electronjohn]

Have you had any success with the lead on that 7JP4? I was giving it some thought, and would think that using a needle-shaped diamond bit in a Dremel might be a good way to whittle enough glass away to solder on a wire. Just thinking, y'know.

[bandersen]

I had some time while waiting for parts to arrive, so I decided to tackle that damaged 7JP4.



I found one lead that was broken off at the glass It was for the vertical deflection so I can test it as is.


It's a runner


I had an old HP CRT from a logic analyzer with burns that's going to be sacrificed for the base. I wrapped it in a blanket and gave it a whack.


I filed down the glass around the broken lead enough so I could solder a new wire. I had it wrapped in a blanket and wore eye protection. Even so, I was very nervous while working on it.
I then attached long, thin wires to thread through the new base.


Here goes nothing!


Success

[bandersen]

Originally Posted by electronjohn

Have you had any success with the lead on that 7JP4? I was giving it some thought, and would think that using a needle-shaped diamond bit in a Dremel might be a good way to whittle enough glass away to solder on a wire. Just thinking, y'know.

Ha - good timing. It was nerve wracking enough with a needle file. I'd be a mess trying to use a dremel. The glass (flint?) files away pretty easily with just steel.

[zenithfan1]

Excellent job Bob!

[bandersen]

Originally Posted by zenithfan1

Excellent job Bob!

Thanks Mark.
BTW that is your 7JP4 on eBay- right? Can't be too many guys in Kenosha with a 7TV5A

Hope you get a bundle for it.

[zenithfan1]

Yep, that's mine. I often wonder how many people in Kenosha have cool tvs. I don't think too many either.

[Zenith26kc20]

Looks like after over 20 years of service (that's right!) Twenty years, one of the 6KV (that's all I could get back then to replace the tubular) ceramic discs in my Motorola VT71M-A failed. I rescued this set from a pile of garbage around two years before that and the owner of the shop I worked in roared laughing when I told him I was going to get it going. I find once these sets are up and running, they are pretty reliable. I just ordered new 6KV caps for the five in the set. I guess it's about time. It's still fun to have this old set running when cable service is needed and thie rest are hidden away!

[bandersen]

I'm finally tackling this TS-18 chassis which is a real mess. I already knew about the missing tubes, HV cage and flyback.

What I didn't expect was wire and component leads to be clipped throughout the set. Some components missing too, but most often just one end is clipped and the part is still hanging in there.

So, I'm starting at V1 and checking every single connection and component in the whole set!



While doing so, I discovered a 10 MFD capacitor that's not in the schematic. It seems to go from the cathode on V4 to the filament node of V8, V9 & V16 (the CRT).

Any idea what this is for? Does anyone out there with a TS-18 have this cap?




Thanks!

[bandersen]

Argh! I just discovered that one deck of the channel selector switch is broken

[bandersen]

I'm not one to give up easily so I stayed up late tonight and repaired that broken switch wafer.

Here's one of my reference photo so I can put it back in properly



It wasn't too hard to remove, but I'd hate to do it without the benefit of a digital camera.
Repairmen must have had great memories back in the day



The offending deck is on the right. The phenolic wafer snapped in two locations.



The tip of the fine-tuning shaft has also broken off



I used a couple drops of super-glue to hold the pieces together. Then, some quick set epoxy for strength. I used a toothpick to apply it to avoid getting any on the contacts.



Finally, I used a little contact cleaner on those silver contacts. Seems good as new. Time will tell.

I'll deal with that fine tuning shaft later. It can be removed fairly easily even when it's back in the set.

[bandersen]

Originally Posted by zenithfan1

You rock Bob, never say die should be your slogan! Great work!

Thanks Mark. I've decided that I'm going to reuse, repair, refurbish parts whenever possible rather than cannibalize another set. I think I'll draw the line at attempting to rewinding a flyback or yoke

Did you see my earlier post about that odd 10mfd capacitor?
Does your TS-18 have it? Unless someone can confirm it does something useful, I'm going to follow the schematic and remove it.

[bandersen]

Here's a better picture of the capacitor in question. The green wire on the + side is soldered to pins 2 and 7 of V4. The negative goes to the 0.005uF and the CRT filament wire (the yellow wire at the top).

I'll just leave it out for now. Once the set is operational, maybe I'll clip it in to see what effect, if any, it has.

[bandersen]

Hey John and Mark I hate to bug ya, but I'm a little confused again!

One lead to my Brightness control is going nowhere


According to the schematic, one end goes to B++ and the other to the Contrast control.

I don't think that's correct though. That end of my Contrast control is going to ground (pin 6 on the 6SL7GT Vert Sweep Output) and it looks original. From what I can make out from Mark's 7VT5 pictures, his Brightness control is going somewhere around the ballast tube. Maybe to ground as well ?




I think that schematic might be missing a dot where the vertical line intersects the "ground" horizontal line. (see attachment)

I'm also wondering if that wire from the Video Amp to the Contrast control should be shielded. Isn't that what the dotted line around it means? My lead is just plain old wire.

Any ideas? Thanks!

[bandersen]

Originally Posted by Eric H

I have an extra TS-18A laying around, looks like the wire goes to pin 3 of the tube directly over it.

No sign of that extra cap on this one either.

Thanks for the quick reply and great photos! pin 3 is B++ and the other side looks like it's ground.