Sencore VA-62A 15MHz kit, cd, etc.
 

I hear that Zenith 6S321 makes, or made, these eprom installation kits. Are they still available?

Thank you;

Lee:smoke:

Did you send him a private message?

Yes. No response.

No activity since 2018.

Anybody know if he's still active?

If this mod is for thr va62 I would like to know more about it
Doug

Yep. But, as I understand it, the eproms vary according to whether you have an early VA-62 or a later production VA-62 or VA-62A. I have the VA-62A.:smoke:

This might get you up to speed on this Doug.
http://videokarma.org/showthread.php?t=253433
http://videokarma.org/showthread.php?t=267686


He also had one or two other threads on the kit.
Use the search on the forums here to find more threads.

I bought a kit about three years ago. I just recently used it.
Then I made a boo-boo when checking out the VA62 (some power supply issues) and blew a chip in the display. I'm still waiting to get the chip from Germany, so I'm kind of dead in the water until then.
I should have completely checked out the VA62 before making the mod.
The kit comes with a CD that contains the service info among other things.

Ah! Thank You.

Scarey mod, that switch.

Power supply problems? Like a bad Lytic? Mine seem to look fine.:smoke:

I replaced two electrolytic caps and a 5 V regulator IC. (So far.)
The big 450V cap on the supply to the Drive Amplifier (sweep drive output) was bad. If I remember right two other supplies were just out of spec. Hum and voltage level. Looking at my notes, both caps were on the main supply, the regulator was on the meter supply. There were also some resistors that looked like they had been replaced but did not match the schematic value or wattage.
This might mean someone tried to correct a problem elsewhere.
The Maintenance manual will be uploaded to BAMA shortly. It has the locations on the board to check voltages and lists the supply limits. That manual has much more in the way of tests and checks, although it looks like you need things like a vector scope for some checks.
There is a main supply board (#900) and another board for the meter and ringer supply (#1900).
Watch those board connectors!

My VA-62A appears to be a virgin. No repairs that I could see. All the big lytics appear to be fine, no buldging, leaking, etc.

Which DPDT Switch did Zenith specify for the mod? Can't tell from the picture.:smoke:

Since Zenith6S321 seems to be MIA at the moment, therefore can't provide the mod kit, the best approach would be to download the EPROM data file from the earlier posted threads. Then send it to Matt's Basement Arcade to have a EPROM burned.
Website; https://mattsbasementarcade.com/
On ebay: https://www.ebay.com/itm/23267907567...gAAOSw3zNak5mR

EDIT: You will need a miniature DPDT toggle switch, for a thick (plastic) panel, like this one.
EDIT: https://www.mouser.com/ProductDetail...YPLoz4kA%3D%3D

You might find it cheaper elsewhere.
The kit included a water slide decal to label the switch, you you have to come up with your own label.
A CDROM with a lot of info was included containing the schematics, operator manual, and a Maintenance (Service) manual.
Most of that info has been uploaded to the BAMA site now.
https://bama.edebris.com/manuals/sencore/va62/

Thanks much. You've been a grand help. I'm piecing everything together, except for the decal, perhaps.

I was poking around inside the Sencore very carefully, pulling and reconnecting all the jumper connections and rebedding some of the ICs in an attempt to restore color output to the test patterns, but to no avail. So I contented myself with giving the interior boards a quick blow of compressed air and cleaned up the inner and outer surfaces of the cabinet. That's all I dare do.

I won't be able to get to it for a few days as I am training a new horse in dressage.

No-Time Tolouse...!:smoke:

Right!
The Maintenance manual isn't really a troubleshooting guide but it has performance checks and adjustments. With the schematics it should be possible to trace the signals with the aid of a scope and of course a meter.
From what I've noticed it is pretty involved with signals going through other boards you might not think are involved.

A "Simplified Guide" has been uploaded to the BAMA site.
It is entitled to be about the VA62A but it fits the VA62 also.
Seems to be intended to be use with a later model RCA TV that has SAW filters instead of the adjustable IF transformers/filters.
https://bama.edebris.com/manuals/sencore/va62/

I just got in this switch, but it's a 3PDT Switch with 9 lugs on the back. Not 6 like shown in Zenith's tutorial. And it's arrayed differently.

I think it's the wrong switch.:smoke:

Nope. Duh. I get it. Just don't use the center three lugs.:smoke:

Well well well, I must of had one less coffee than I needed.
I made a mistake somewhere along the line, I don't know where I made the mistake that you need a 3PDT switch! I'm going to have to go back through my posts and make the correction. Zenith's switch diagram shows it to be a DPDT.
DPDT is what his text says.
Thanks for pointing this out. No one including myself noticed it.
The switch only needs to be a DPDT.

I did the chip swap, and that worked fine. Every function was preserved, and the MHz Programming goes waaay beyond the stock 35-50 megs.

Then I added the switch, and that seems to work ok, but when engaged up or down in makes a little electronic burp, ever so slight. Plus, the unit lost its 39.75, 41.25, and 47.25 MHz trap settings. They all come up reading too low in frequency.

Why? And, do I really need the switch?:smoke:

If you read all of the posts Zenith made he mentions that sometimes the PLL (Phase Locked Loop) oscillator will not lock on the frequencies at the extreme limits and toggling the switch could jog it into operating. So the switch might jog other things unfortunately.
Even though the RF-IF switch is set to 30-50MHz (IF frequencies), the change in the EPROM program really uses the RF oscillator section, not the IF oscillator when you select a frequency outside the normal range.
As designed the RF oscillator selection powers up the RF output amplifier not the IF output amplifier. The IF amplifier puts out a signal that is 100 times larger than the RF amplifier. (The TV tuner has a gain of about 100.) So the RF amplifier output is too small for use injecting into the TV IF. On the other hand the IF amplifier output is so large it would overload the TV RF (antenna) input. The switch mod allows you to select whichever output amplifier (level range) you want.

The reason for the "low" trap settings is that they are not "low"at all. They are tied to the MHz setting I dialed up, in this case 22.75 which in turn spits out 16.75, 18.25, and 24.25 MHz on the three Trap settings of 39.75, 41.25, and 47.25 respectively.

But here's a big problem. My scope doesn't pick up or measure ANY of these new custom readings.

I don't know.
I wish the part I ordered would arrive so I could try my unit.
The guy supposedly sent another one after the first got lost.