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  #46  
Old 04-16-2012, 08:43 PM
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Zenith6S321 Zenith6S321 is offline
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VA62 EPROM mod. clarification

I edited my post #31 to clarify the wiring of the DPDT RF/IF Level switch. Attached is a picture of the VA62 block diagram showing the RF-IF Switch wiring with its numbered wire connections. There was a mistake in the schematic that I corrected in pencil.

Last edited by Zenith6S321; 09-09-2016 at 11:48 AM.
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  #47  
Old 04-17-2012, 09:01 AM
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Dave's reprogramming of the uP for the Sencore VA62 is ingenious.
I received his EPROM yesterday and installed it this morning. My VA62 can now go down to 12.0Mhz but at that low frequency the amplitude is subdued and waveform a little malformed.

But, that is a non-issue. Don't need for it to go that low frequency anyway.
My VA62 produces a nice waveform and good amplitude down to 15.0Mhz:



Here it is at 18.5Mhz:



Here at 26.30Mhz:



Here at 42.75Mhz:




Have not installed the toggle switch yet.
Need to visit Radio Shack for a nice looking switch.
Think I will put masking tape on the inside to capture metal filings.

Carl
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Last edited by cwmoser; 04-17-2012 at 09:17 AM.
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  #48  
Old 04-17-2012, 12:50 PM
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Followed the schematic and got the DPDT switch installed.
What a pain in the a**!!
Its really tight in there. I cut loose the cable straps and got the switch installed. Looks like everything is working as described. I did note that when a signal did not occur, toggling the switch brought it out - like Dave noted.



Now, I got to spend some time learning how to use this to align vintage TVs.

Carl
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  #49  
Old 04-17-2012, 06:20 PM
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Nice work Carl, I'm glad the installation went well! I must have checked my RF/IF switch wiring four times just to be sure I had the wiring right since I did'nt want to mistakenly send the -15VDC to the +15VDC, and vice versa, to the wrong RF/IF amplifier power inputs. I also found it a bit tough to fit the new DPDT level switch in the panel but I think its the right placement. I find that I forget which RF-IF SIGNAL switch positions can can work with the DPDT in the RF or the IF position so I may tape a copy of the list on my VA62 for reference. Good to hear that toggling the new RF/IF switch persuades your VA62 PLL to lock in the same as mine.

Dave
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  #50  
Old 04-18-2012, 07:27 AM
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Very nice mod that Dave developed.
Makes those old Sencore VA62's very useful on vintage TVs.

Anyone have suggestions on the best way to learn the fine points about aligning IF in TVs? I watched bandersen's video and I guess just jump on a TV and experiment. Too bad we don't have hands on instructional classes anymore. Might be a consideration at a future ETV Convention or Radio swap meet.

Carl
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  #51  
Old 05-08-2012, 07:44 PM
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Some more info on the modification

For anyone interested in the modification that allows the Sencore VA62 to be used to generate TV video/audio modulated IF for any frequency from 15.75MHz to 35.25MHz as well as the original 45.75 MHz, attached is a document describing the installation, whats modified, and its new capabilities for the EPROM plus RF-IF switch modification. I can supply the EPROM for $5.00 and USPS first class flat rate shipping is about $6.25 IIRC. Or I can send you a .HEX file if you want to burn you own EPROM. YOU WILL have to install an RF-IF manual level switch to get the IF level output for the 15.75MHz to 35.25MHz range (on channel 42).

Dave
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File Type: txt SENCORE VA62 1-99MHz CH42 Modification EPROM.txt (2.5 KB, 131 views)
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  #52  
Old 05-10-2012, 10:41 PM
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Sencore VA62 vs VA62A

I have been asked whether there are any differences between the Sencor VA62 and the VA62A. I have always thought they were functionally identical. Can anyone shed any light on this subject?
Thanks,
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  #53  
Old 05-12-2012, 08:59 AM
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Quote:
Originally Posted by TubeType View Post
I have been asked whether there are any differences between the Sencor VA62 and the VA62A. I have always thought they were functionally identical. Can anyone shed any light on this subject?
Thanks,
I posed the same question some time ago and the answer I got was that the only difference between the VA-62 and the VA-62A was that the "A" version extended the UHF channel range. Today that is so little an issue that I would go after the best condition/price and not consider if its "A" or not.

Carl
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  #54  
Old 05-12-2012, 09:40 AM
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Thanks Carl,
That's why I never noticed the difference between the two boxes. I'll pass that info along.

Quote:
Originally Posted by cwmoser View Post
I posed the same question some time ago and the answer I got was that the only difference between the VA-62 and the VA-62A was that the "A" version extended the UHF channel range. Today that is so little an issue that I would go after the best condition/price and not consider if its "A" or not.

Carl
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  #55  
Old 09-09-2012, 07:16 AM
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Has anyone used a modified VA-62 to align a vintage TV?

Carl
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  #56  
Old 09-09-2012, 08:56 AM
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wow that one's cool, i have the sencore va-48 its not as modern as that one is.
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  #57  
Old 09-09-2012, 10:12 PM
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I just picked up a VA-62 this week. I'll send you a PM concerning the chip.
Thanks,
Phil
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  #58  
Old 09-17-2012, 08:47 PM
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chip modification offer

Dave,
Are you still offering the modified chip?
Thanks
Phil
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  #59  
Old 09-18-2012, 07:05 PM
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Zenith6S321 Zenith6S321 is offline
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Yes, did you get the PM I sent?

Dave
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  #60  
Old 09-19-2012, 03:40 PM
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Just got it.
Thank you
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