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  #16  
Old 03-02-2012, 07:54 PM
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bandersen bandersen is offline
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Quote:
Originally Posted by Kevin Kuehn View Post
.. I bet with a little program hack and a new eprom burnt, one could have that thing singing down in the 20Mc band...
There has been some some progress made on this front. I'll know for sure in a few days...
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  #17  
Old 03-09-2012, 09:49 PM
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A VK member sent me a modified EPROM that unlocks the frequency input. It's a 2716 and mine had a 2732 EPROM, but it seems to work fine

The amplitude is a little reduced and there is some distortion on frequencies I tried, but overall it works just fine. I expect the output amplifier is designed for the 35-50 MHz range so some attenuation is to be expected outside that range.



21 MHz and 66 MHz
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Last edited by bandersen; 03-09-2012 at 09:54 PM.
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  #18  
Old 03-10-2012, 01:38 AM
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Excellent!
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  #19  
Old 03-10-2012, 08:30 PM
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Zenith6S321 Zenith6S321 is offline
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VA62 EPROM modification

As an avid reader of these forums I came across Bob's post about wanting a wider frequency range on the VA62. A few months ago I did my first restoration on a 721TS and found out how touchy analog RF generators are to use for a marker generator. I happened to have a VA62 and its schematics which I used to fix its 1MHz reference to the PLL. Back in the day I did some digital design work. So, like Jeremy Clarkson of Top Gear (love that show) I figured "how hard could it be?". I read the EPROM, used Google to find a dissasembler, and spent a few evenings looking through the schematics and the 28 pages of assembly code. I found the code that limits the keypad frequency input to 35.00 - 50.00 MHz and changed the limits to be 3.00 - 99.00 MHz. As Bob's cool video shows, the VA62 is designed for the 35-50 range, but will work outside that range to some extent. My Run 18 VA62 can reliably be programmed for 15.00 - 99.00 MHz. Below 15 is hit or miss. My VA62 uses a 2716 2K Byte EPROM, but the schematic shows a jumper to accomodate the 2732 4K Byte EPROM that Bob's has. The 8035 microcontroller can address two 2K Byte program memory banks. It would be useful to know if there are different firmware revisions or if they all use the same version. If you want to mod your VA62 PM me. I can supply the .HEX file if you have an EPROM burner or I can burn your EPROM if you send it to me along with a prepaid box to ship it back to you. As Bob's video shows the mod requires opening the VA62, removing the old EPROM and inserting the mod EPROM. This static sensitive electronics, so you do this at your own risk.

Last edited by Zenith6S321; 09-08-2016 at 08:47 PM.
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  #20  
Old 03-11-2012, 06:24 AM
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Quote:
Originally Posted by Zenith6S321 View Post
As an avid reader of these forums I came across Bob's post about wanting a wider frequency range on the VA62. A few months ago I did my first restoration on a 721TS and found out how touchy analog RF generators are to use for a marker generator. I happened to have a VA62 and its schematics which I used to fix its 1MHz reference to the PLL. Back in the day I did some digital design work. So, like Jeremy Clarkson of Top Gear (love that show) I figured "how hard could it be?". I read the EPROM, used Google to find a dissasembler, and spent a few evenings looking through the schematics and the 28 pages of assembly code. I found the code that limits the keypad frequency input to 35.00 - 50.00 MHz and changed the limits to be 3.00 - 99.00 MHz. As Bob's cool video shows, the VA62 is designed for the 35-50 range, but will work outside that range to some extent. My Run 18 VA62 can reliably be programmed for 15.00 - 99.00 MHz. Below 15 is hit or miss. My VA62 uses a 2716 2K Byte EPROM, but the schematic shows a jumper to accomodate the 2732 4K Byte EPROM that Bob's has. The 8035 microcontroller can address two 2K Byte program memory banks. It would be useful to know if there are different firmware revisions or if they all use the same version. If you want to mod your VA62 PM me. I can supply the .HEX file if you have an EPROM burner or I can burn your EPROM if you send it to me along with a prepaid box to ship it back to you. As Bob's video shows the mod requires opening the VA62, removing the old EPROM and inserting the mod EPROM. This static sensitive electronics, so you do this at your own risk.
The Tron Gods are truly among us.....

I've gotta see if Dad's VA62 is still among his stuff. He sold one that I know of (Dad had three VA62's at one point, only two of which worked).

Say......you wouldn't by chance know how to modify an RCA CT100 so that it accepted a Portacolor 10VAHP22 CRT, would you???

Cheers,
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  #21  
Old 03-11-2012, 10:47 AM
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Excellent work guys!

Everybody just go easy on the bidding wars on the VA-62's.
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  #22  
Old 03-11-2012, 03:22 PM
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ChrisW6ATV ChrisW6ATV is offline
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Quote:
Originally Posted by Zenith6S321 View Post
I read the EPROM, used Google to find a disassembler...
What a great service that was to the restoration community. Stories like this make me appreciate the members and want to contribute as well.
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  #23  
Old 03-12-2012, 07:18 PM
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Zenith6S321 Zenith6S321 is offline
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Thanks for the kind words. I grew up dragging home old TV sets and back then they were all tube models so I have a soft spot for them. Among them was what I now know was a Dumont RA-109 and a CTC-5. Anyway, another VK member asked if it would be possible to get video and audio modulation with a programmable frequency. I did hook up my VA62 set for 45.75 MHz to my RCA 721TS set to channel 1 and got both video and audio. There are only a dozen or so unused locations in the EPROM, so don't hold your breath.

Dave
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  #24  
Old 03-12-2012, 08:32 PM
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It doesn't look like the signal rolls off too bad yet at 21Mhz, and probably not even worth messing with it considering the variable output level. Could they have used another PLL as a programable bandpass filter, or would it more likely be a simple high pass op-amp stage on the output?
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  #25  
Old 03-12-2012, 09:36 PM
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Zenith6S321 Zenith6S321 is offline
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A quick look at trying to change the 45.75 MHz to be programmable finds that its not controlled by the PLL. It has a separate fixed source. I will investigate Brian's origiinal request for replacing the programmable cable function (chan 2-73 with +/- 9.75 MHz offset) with a programmable frequency.

No clue here about the passband of the analog amps that might cause a low frequency attenuation.

Dave
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  #26  
Old 03-13-2012, 01:15 PM
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Phil Nelson Phil Nelson is offline
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I loaned my photocopies of the service manual to a fellow collector (Tom K.) and he scanned the schematic and parts list. This is 100 megabytes of material.

I'll be happy to share it, but I don't want to post anything that size permanently on my website.

If you're interested, let me know and I'll figure out a way to get the files to you, either by temporarily posting on my website for download, or by mailing you a CD.

He also provided a scan of the (22-megabyte) operations manual, but I gather that some people already have that. Anyway, same deal there -- let me know if interested.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

To send me email, kindly go to http://antiqueradio.org/contact.htm .
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  #27  
Old 03-16-2012, 12:58 PM
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Phil Nelson Phil Nelson is offline
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On request, I posted the VA62A files temporarily on my website.

Operation & Application Manual (22 megabytes):

http://antiqueradio.org/art/temp/VA62Desc&Oper.pdf
http://antiqueradio.org/art/temp/VA62Rcv&MonApps.pdf
http://antiqueradio.org/art/temp/VA62VCRApps.pdf

Schematic & Parts List (100 megabytes):

http://antiqueradio.org/art/temp/Sheet1a.pdf
http://antiqueradio.org/art/temp/Sheet1b.pdf
http://antiqueradio.org/art/temp/Sheet1c.pdf
http://antiqueradio.org/art/temp/Sheet1d.pdf
http://antiqueradio.org/art/temp/Sheet1e.pdf
http://antiqueradio.org/art/temp/Sheet1f.pdf
http://antiqueradio.org/art/temp/Sheet1g.pdf
http://antiqueradio.org/art/temp/Sheet1h.pdf
http://antiqueradio.org/art/temp/Sheet1i.pdf
http://antiqueradio.org/art/temp/Sheet1j.pdf
http://antiqueradio.org/art/temp/Sheet1k.pdf
http://antiqueradio.org/art/temp/Sheet1l.pdf
http://antiqueradio.org/art/temp/Sheet2a.PDF
http://antiqueradio.org/art/temp/Sheet2b.PDF
http://antiqueradio.org/art/temp/Sheet3a.PDF
http://antiqueradio.org/art/temp/Sheet3b.PDF
http://antiqueradio.org/art/temp/Sheet4a.PDF
http://antiqueradio.org/art/temp/Sheet4b.PDF
http://antiqueradio.org/art/temp/Sheet5a.PDF
http://antiqueradio.org/art/temp/Sheet5b.PDF
http://antiqueradio.org/art/temp/Sheet6a.PDF
http://antiqueradio.org/art/temp/Sheet6b.PDF
http://antiqueradio.org/art/temp/Sheet7a.PDF
http://antiqueradio.org/art/temp/Sheet7b.PDF

To download a file, right-click on the URL and choose Save Target As...

Grab these files now if you want them, as I won't keep 'em up there forever.

Regards,

Phil Nelson

Last edited by Phil Nelson; 04-17-2012 at 11:39 PM. Reason: Fixed typo in one URL
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  #28  
Old 03-16-2012, 07:09 PM
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Kevin Kuehn Kevin Kuehn is offline
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Boy that is one congested piece of test gear.

From what I gather, it sounds like the output level was factory programed to a flat response at the various RF/IF frequencies for each individual VA-62. So any variation at lower IF frequencies is likely coincidental and would need to be programed out via Eprom.

Are you guys pursuing these units to use as an IF marker generator; to be used along with another sweep generator? Or are you planning to use the Sencore multiburst modulation method of IF alignment?

I'm curious just how well the Sencore multiburst alignment method caught on with repair techs? For my hobby use I think I'll prefer to stick with the old tried and true scope method of actually seeing the IF response curve on a scope. I can however see the practicality of the burst method for a busy repair shop.

Last edited by Kevin Kuehn; 03-16-2012 at 11:44 PM. Reason: spelling
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  #29  
Old 03-16-2012, 08:53 PM
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bandersen bandersen is offline
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I'm planning on using it as a programmable IF/RF and marker generator. Many of the sets I have require peaking each IF coil at a specific frequency then double checking the overall response cure with a sweep gen. and markers.

I'm curious about the Sencore method though. I've only read about it briefly in the manual.
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  #30  
Old 03-16-2012, 11:26 PM
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Zenith6S321 Zenith6S321 is offline
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I'm a novice at alignment, but I wanted a digital frequency marker generator for the lower IF frequencies for the older sets.

It was suggested to me that it would be useful to get an video and audio modulated IF output from the VA62 in the 15-35 MHz range. At the moment I am testing a modification that causes one modulated Cable channel number to output in that range. The +/- .25 MHz steps let you shift its frequency across +/- 9.75 MHz. I have this mod coded and it seems to work OK, but I need to make sure I did'nt break any other function. More testing is needed.

Also, it looks like a physical modification will have to be made to get IF output levels as the VA62 is set to output RF levels in the cable switch positions. Suggestions would be appreciated. I was thinking of adding a switch, but I think it will need to be a triple pole double throw.

Dave
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