Ok. Let’s try this again…RCA 9TC240 Alignment

[Chris K]

Originally Posted by Penthode

It is not as simple inserting composite video in this set compared to the 721. I have a 721 and the picture is excellent through the tuner and IF. The set you are working on is better but if all you are interested in is getting a picture on the screen, yeah that will work.

Gonna keep on keepin on!

[Penthode]

Originally Posted by Chris K

Gonna keep on keepin on!

Great! You mentioned the trap null adjustments were okay?

What does the sweep look like on your scope? It can be made to match the published curve. I have done it with the equipment you are using. Can you detail what you are getting?

[Chris K]

I’ll be working on it Thursday night.

[Penthode]

[Chris K]

Originally Posted by Penthode

I picked up the spare chassis today...3 of them. I want to swap out the brightness control first thing then do a quick reassessment of all the steps. I'm starting to know all of them from memory! I may not be able to get what I should but I sure as hell know the procedure by now. That's a big advancement for me.

[Chris K]

The parts pieces have the fabric fine tuning/pulley strap intact. I wonder if there's a way I can make it more supple and less prone to breakage when I remove it? I've rigged a rubber replacement for my TV but because it stretches, there's backlash when you fine tune the set.
EDIT: Actually it looks like leather.

[Penthode]

I used a leather strap. Bought some thin leather from Hobby Lobby. Cut a long strip of correct with a razor blade. Pre-stretch it then cut the strip a slightly longer than needed. Then with the razor blade cut taper (sloping) ends and then lap the ends together with a dab of white glue or super glue and clamp until glue is hard with a pair of pliers. Belt still working fine on my KRK5 tuners (three of them) with no slip after 20 years.

The same method was used for the mandrel drive belts on the earliest Edison cylinder phonographs from 1888 thru 1912 except they used fish glue. ( I have a 1900 Columbia AT, 1901 and 1903 Edison Model A Standards, a 1906 Edison Model B Triumph and a 1910 Edison Fireside which have belts made this way and play faultlessly).

Here is a YouTube video of the process.
https://youtu.be/NF9A-_xMBck?si=3yBpeNXUjuekhMDD

[Chris K]

Very cool. I replaced the brightness control and there’s still intermittent full brightness even when it’s turned all the way down. Something else going on with that. Anyway I got into the alignment process and the damn HP 8600 Digital Marker went all wonky again and wouldn’t display frequencies. I’m not going to be able to keep using the screwdriver tap method on this anymore to get it to work. I’ll do some troubleshooting but does anyone know of a similar instrument that would work with the HP sweep generator I’ve been using? No 8600s on eBay at the moment.

[Penthode]

No the HP 8601a/HP8600a are a unique pair. The HP8600a is a very reliable unit. What do you mean it is not reading frequencies? How are the switches set?

[Chris K]

It’s not a setup or connection issue. This is an intermittent issue where all the frequencies read zero or when in CW more an inability to lock in on frequency. The cure for this has been shock to the unit with a tap with a screwdriver or picking up the front and dropping it an inch etc. it’s something inside that’s very subtle and is going to be a SOB to run down. It’s been an issue since I got the thing. This issue has been more frequent since I put the unit in a stack of other equipment so I’m going to pull it out, get it working again and have it just stand alone. But this kind of issue isn’t going to be easy to run down. It’s a fault somewhere in one of the boards. I’ve tried cleaning the plugin contacts and making certain they are seated well but that’s about as far as I’ve gone. I don’t think it’s an issue I can fix. I’ll just have to live with it until I can get another unit.

[Kevin Kuehn]

It sounds like a intermittent solder joint. Requires opening things up and applying pressure to various areas with a length of wood dowel in attempt to isolate it to a smaller area. Eventually you can hone in on it, but often takes a lot of time.

[Chris K]

Originally Posted by Kevin Kuehn

It sounds like a intermittent solder joint. Requires opening things up and applying pressure to various areas with a length of wood dowel in attempt to isolate it to a smaller area. Eventually you can hone in on it, but often takes a lot of time.

Yes that’s what I think. More than likely in the main board and not one of the modules. The main board is more susceptible given it’s a horizontal board and will flex. I’ll be working on it tonight

[Penthode]

It uses cards on connectors. It is made by HP and should be nearly bullet proof.

I would simply open the box and reset the connectors and cards and VOILA it will work again.

[Chris K]

Originally Posted by Penthode

It uses cards on connectors. It is made by HP and should be nearly bullet proof.

I would simply open the box and reset the connectors and cards and VOILA it will work again.

I did and cleaned the connectors again and made sure everything was seated firmly. I reassembled it after pulling off the 30 lbs of equipment on it and it's working fine. Time will tell but as long as it's operating, I'll get back on it tonight.

[Chris K]

Originally Posted by Penthode

I may not be available in the morning so here goes. The table measuring at the junction of L104 and R126 is impossible because on my diagram there is no junction.
The reason your VTVM goes off scale is because there is a DC bias of at least 10vdc there.
To adjust the traps do this:
Connect the VTVM to pin 1 of V106 and ground.
Switch the VTVM to the 5vac range. Not DC.
Next switch the HP8601a AM modulation on to 1kHz.
Adjust input RF until you see about 3 volts AC on the VTVM
Adjust the traps null at frequency specified.
Raise the RF level as necessary to keep the null at no less than 1 vac.
Repeat this for each of the trap frequencies.

So I'm starting the trap adjustments over again. Just to confirm the procedure outlined above is after removal of V107 substituting the potentiometer I made and adjusting it to -4.5V DC at resistor R135/R136 junction?