Sencore VA-62
 

I took a gamble and picked up one of these in unknown condition for about $50.

http://farm8.staticflickr.com/7063/6...cc22488f_b.jpg

I crossed my fingers and powered it up. It actually seems to work properly :banana:
I don't have any manuals, but I think I can figure out the basics. All the RF-IF modes seem to work. It would be so, so nice if the programmable IF could go down to 21 MHz, but it bottoms out at 35.

I haven't tried the Ringing Test or Drive Signals yet. I think I'll need a manual for that.

Below are the test patterns on my Panansonic Tau TV. I suspect the flaws are in the TV and not the Sencore. Can anyone clue me in on what the 'Chroma Bar Sweep' is for ?

Crosshatch and Dots
http://farm8.staticflickr.com/7156/6...cd2ba78a_m.jpg http://farm8.staticflickr.com/7028/6...7272d0bc_m.jpg

Multi-burst Bar Sweep and Staircase
http://farm8.staticflickr.com/7067/6...d8aeb8f3_m.jpg http://farm8.staticflickr.com/7030/6...b6a542d9_m.jpg

Color Bars and Chroma Bar Sweep
http://farm8.staticflickr.com/7173/6...05c00a9e_m.jpg http://farm8.staticflickr.com/7057/6...664b6674_m.jpg

Bob-

The chroma bar sweep is for alignment/bandpass testing and adjustment if I remember right. I have a VA-48, the predecessor to your unit, and I bought a manual for it from Sencore about 10-15 years ago. Some Photofact manuals perhaps in the 1980s had scope pictures of the chroma bar signal in various circuits. I think you got a bargain!

Nice looking patterns. I wonder how they manage the RF programing on this. Is it new enough to be micro controlled, or more likely some custom analog chip set? I'd have to get right inside and look things over.

Thanks for the info. I've read these are tricky to service so I'm really glad it's working :yes:

I will be soon as I need to clean some dirty controls. I'll let you know what I find.

Early 80s technology at it's finest. The chips are date-marked late 1983 / early1984 There's an 8035 microcontroller at it's heart. I assume the RF is done with a programmable PLL.

http://farm8.staticflickr.com/7044/6...e67f7cff_z.jpg http://farm8.staticflickr.com/7017/6...a91ccc51_z.jpg

http://farm8.staticflickr.com/7029/6...efd688c2_b.jpg

Wow! That was obviously an expensive piece back in the early 80's. I bet with a little program hack and a new eprom burnt, one could have that thing singing down in the 20Mc band. But don't ask me how. I always though some of their 60-70's gear was made sort of on the cheap, but this thing looks first class, fiberglass pcb's and all.

It might be easier than that. Assuming this uses a PLL, there should be a hi-speed digital divider in the feedback loop. Something like ÷ 256.

Perhaps that could be tweaked to ÷128, so it would put out a frequency 1/2 of what the display shows. 22 MHz instead of 44 MHz for example. Then add a range switch so it could do 17.5 - 25 Mhz or 35 - 50MHz. :scratch2:

You're probably onto something there. The schematic should reveal if it's divide by 256.

Unfortunately, I don't have manuals other than the quick start guide I found tucked inside. Anyone out there have a schematic ?

I paid around $1.5K for one of these back in 1986. I never had a minutes trouble with mine. I sold mine with the manual included.

I have the bound 100-page operations manual and a photocopy of the monstrous service manual. Someone let me borrow his service manual to photocopy onto 11x17 pages. The original has a number of super-sized pages that cleverly unfold to about the size of a card table. I brought it to Kinko's to copy on their big fat machines and it was still a bit of a trial. Not something I could readily scan on our dinky home printer.

The operations manual is interesting, although the basic VA62A functions are pretty evident if you look at the front panel.

Phil Nelson

I wonder if you contacted Sencore ... maybe they have a Tech Bulletin for altering the IF frequency?

Carl

Perhaps. I also found a few places that sell the user and service info.

Bob,

I'll do some digging - my Dad had two, sold one, and likely kept the manuals. I fixed his several times, first the meter would act funky, then the power supply couldn't be monitored. Turns out there are some protection diodes across the input of the meter - I got the replacements from Mouser and fixed the metering problem.

Sadly, Dad passed away December 30th, and won't be needing his VA62 or the manuals...

Brian

I'm sorry to hear about your dad and thanks for the offer. bharris kindly emailed me a pdf copy of the Operation and Application manual, but I could still use the schematics and service info. Looks like I can get them from Tucker: http://www.etestmanuals.com/Search.aspx?Mfg=SEN

There has been some some progress made on this front. I'll know for sure in a few days...

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 :banana:

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.

http://farm8.staticflickr.com/7059/6...aee4c119f0.jpg http://farm8.staticflickr.com/7054/6...0e07fd8e08.jpg

21 MHz and 66 MHz
http://farm8.staticflickr.com/7050/6...5a2f915d2e.jpg http://farm8.staticflickr.com/7176/6...1365a2f5d8.jpg

Excellent!

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.

The Tron Gods are truly among us.....:ntwrthy: :D

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??? :scratch2: :D

Cheers,

Excellent work guys! :thmbsp:

Everybody just go easy on the bidding wars on the VA-62's. ;)

What a great service that was to the restoration community. Stories like this make me appreciate the members and want to contribute as well.

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

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?

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

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 .

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

Boy that is one congested piece of test gear. :yes:

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.

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.

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

Low band IF and level modification
 

Here are some pictures of what I ended up with to make the VA62 output an IF level modulated signal for the 15-35 MHz IF band and IF level. I found an error in the VA62 block diagram showing the wiring for the RF-IF Signal switch. The corrected wiring diagram made adding a manual RF/IF output level switch easy. One piicture is a dagram of the switch with the circled numbers that are the terminal number of the wires removed from the RF-IF Signal switch that are wired to the new manual DPDT RF/IF level switch. The pictures show before and after the switch addition.

My software modification to the VA62 EPROM uses the Prog Cable setting of the RF -IF Signal switch to change the frequency of channel number 42 to 25.5 MHz. Pressing the +/- keypad key then lets you enter an offset to shift the frequency by +/- 9.75 MHz in .25 MHz steps. There are some pictures of channel 42 with a +9.75 MHz and a -9.75 MHz offset with the output frequency displayed on a frequency counter. There are scope pictures that show the waveform and voltage level.

I have not tried it with my 721TS, or tested it thoroughly, but everything else still seems to work properly.

Same offer as before, send a PM and I will send a copy of the EPROM .HEX file for you to burn a copy of the modification. Or send me your 2716/2732 EPROM (keep your original safe) with an addressed, prepaid shipping, box and I can burn it for you.

Dave

Clarification: The numbers on the DPDT level switch diagram are the RF-IF Switch (gray one at the top of the 4th picture) numbered solder connection points. Remove the wires connected to the RF-IF switch solder connection points 8,9,10,14, and 17 and then connect those wires to the DPDT switch as shown in the diagram. The DPDT switch will then either supply power to the RF or the IF amplfiers depending on the position of the new DPDT RF/IF Level switch.

And a few more pictures of the modification.

Testing the mods on RCA 721TS
 

Although the scope and frequencies look right, the best test is to try the 25.75 MHz modulated video and audio on an old set. Attached are some pictures. First I hooked the VA62 up to the antenna leads and sent video and audio on channel 3, the first two pictures.

Then, in the last three pictures, I hooked the modified VA62, set to 25.75MHz, up to the third, second, and first picture IFs and set the VA62 levels accordingly. It worked! :banana:

Testing the mods on 721TS contd.
 

I also tried the audio IF and it also worked, although my VA62 tones. I also found my video response rolls off at between 3.0 and 3.5 MHz using the VA62 multiburst bar sweep.

Dave

Nice to see the results clearly on the CRT.

Very impressive, Dave. Now I want to see someone do a bar sweep IF alignment on a vintage set. :thmbsp:

They explain the Sencore bar sweep alignment method in my 1980's vintage school text book by Kiver. They're using the older VA-48 but I'm sure the process is the same. You really need to have a solid grasp on how the IF response curve works in order to relate that to what's showing up on the sets CRT. At my basic level of alignment experience, it just seems very confusing. :scratch2:

I have a VA-48, and also Milton Kiver's excellent book about the B&K 1077 (Television Analyzing Simplified). Can you tell me what book you have with Kiver explaining the Sencore device? Thanks.

Chris,

I was off on the year. It's a 1973 revised text that we used in school. Basically an update of the older Kiver works. If fact much of it reads the same as my 1949 edition, only this is updated for the newer sets and test equipment.

I can try to scan the VA-48 pages. I think there's about 8 pages. If interested pm me an email.

I'm with you Kevin. My 721TS is the only one I have attempted, and I never did get decent audio. I read through Phil's scan of the manual (thanks very much Phil!) and also found the Sencore VA62 burst alignment confusing. But maybe someday it will sink in to my thick skull.

Dave

Something tells me Bob probably has the burst bar sweep alignment method mastered by now. He's been very quiet. ;)