Great. As if I didn't already see this dam print on the inside of my eyelids. A switch that shorts VR6002, and an unidentified set of relay contacts.

I expect that the relay switches between record and playback. Fixed tracking for record and adjustable tracking on playback.

I know Tom, I've been perusing the print all week. Record is ALWAYS VERT/TACH coincidence. There's no 'tracking' to it.

The point was, that that contact set did not exist on the earlier version and that it is not designated by so much as a dashline to the actuator or another contact set. Neither is the remote tracking pot and switch designated where it enters the board. This barely qualifies as 'halfass documentation'.

The off-board remote part is everything inside the dashed lines labeled "TRACKING". The physical connectors to the board are shown by the three open circles. Which is sort of confusing at first because the relay is also shown with three circles. And the relay is on the servo board, even though it's drawn outside the lines.

It's also not at all clear that the relay contactng the solid triangle means "playback" and the open triangle is "record". You can sort of infer that from looking at the other relay contact that sends the control pulses one way or another, but that's way over in another part of the schematic.

You can sort of figure how this happened. The PX-A505 board is identical to the older PX-506, with the exception of the tracking control. So some poor junior Akai engineer who got the job of redoing the schematic said "Ah so! I simpry erase line on edge, draw in tracking control in brank part. Sayonara."

Anyway, I jumpered the lower two points of the tracking control connection together which gives the effect of providing +9 V. to pin 8 of IC-6004 via 139K of resistance, which in retrospect is probably pretty important to its operation (duh), given that it goes right to the base of one of the internal transistors.

I powered it up and got a definite improvement. I can now get a stable image vertically with just some slight random sideway pulling. I was then able to improve it further by adjusting the input and exit tape guides that control the height of the tape as it wraps around the drum. At the same time, I discovered that the input tape guide was actually coming loose, which no doubt wasn't helping the image stability at all, so I carefully tightened it down to the head assembly base plate.

Tomorrow I'll try to add a pot to the tracking section to see if I can improve things that way. Then I'll go through the servo board alignment procedure - it's like two pages worth of adjustments in the manual. So although it's still way too soon to declare victory, it looks like we're finally making some progress.

Vertical display stability in helicals depends heavily upon the entrance guide. That's where V sync gets reproduced. You don't have a reference tape to set it with, and even if you did after all this time it would no longer be reference. If you can get it to play ONE tape, that it didn't make yesterday, it's a major achievement.

Trust me, I've only been working on helical video since 1969. Not that I understood all the parameters at the time, but shortly later I did and today it tends to fall into the TMI category.

I've been simply just too bummed to write anything about this project for several days now. Here's what happened: if you recall, I was finally getting some wobbly video from my VT-100. I figured a complete adjustment of the servo board couldn't hurt. So I carefully went through all of the adjustments in the manual. Turns out all but one were already exactly correct.

Then I took another look at the monitor to see how much that improved the picture .... and found a blank raster. That's right, now in play mode I'm getting nothing. No pulling or tearing, not even any noise, no video at all, just a plain blank raster. Arrrrrggghhhhh!!!!!!

Blast. Well, tape that old is probably shedding like a Samoyed in June. Mostly when heads clog you still see noise as RF AGC goes wide open. But could also be muting, can't say if that set has that feature.

Worse, the 'convenient' solvents like isopropyl and freon substitute don't dissolve binder. Got any left over xylene laying around?

This is beginning to sound like one of my plumbing projects.

You'd think, but no, much to my surprise, all my tapes are in excellent shape, thanks no doubt to having been stored in plastic bags in a temperature/humidity controlled environment (my living room) all these years.

And the funny part is that I decided to give it another try today, and now it's working again. Go figure. Anyway, after watching the monitor for a few minutes, it looks like some sort of horizontal sync problem. I can get the image to stop rolling vertically using the vert hold, but it's tearing side to side, sort of like trying to watch the old SSAVI scrambled cable channels back in the day. All I know for sure is that the servo board is now working properly.

Unless anyone has a better idea, I'm going to try scoping the video output to see if I can get a clue there. I want to see what the sync pulses look like.

After all this time, bad caps and bad solder connections are likely. If your video comes and goes it might be very time-consuming to scope out the problem, but there isn't much else you can do. First thing I would do is try to find out if the problem is thermally related or just bad connections. In video circuits a marginal capacitor will often cause rounded edges of a waveform; time to sit down and watch a bunch of waveforms at various test points.

Scope video out at around 20us/d. See if H is a nice sharp box or a bowl. The TV may simply be unable to find it. For that matter, the scope may not be able to find it.

SUCCESS!!!

When last I posted to this thread, I was totally bummed because in quick succession, my video output vanished and then the capstan solenoid wouldn't kick in when you hit Play. Well it took me this long to get un-bummed. In the meantime, I managed to find another VT-100, figuring it might have some useful parts in it (I tried it out and of course it didn't work).

So I started with the video board from my original deck. This is a real pain to work on because it's mounted to the top of the deck frame directly beneath the supply reel, so there's no way to test it while playing a tape. So I connected my camera to the video input to act as a video source. I then quickly found that the second video amp, an Akai LM-1, was dead. This is not the first time that's happened. This board had the same problem many years ago. And way back then, I bought a spare LM-1 in case I might ever need one. Well, now I needed one. And by some miracle, I knew axactly where it was. I swapped it in and hey presto, video appeared.

Then I swapped in the servo board from the new VT-100 I bought. I quickly found that the first FF-10 IC in the phase control half of the board was dead, just like on my original board No big shocker there. Fortunately, I still had two extra FF-10 clones that ARF member Matthew made for me last year. In it went, and then I discovered that the next FF-10 was also dead. So I soldered in my last FF-10 clone and tried it again. (That pesky FF-10 is clearly the Achilles heel of the VT-100).

This time I was rewarded with a perfect trapezoid wave on TP-4 along with a nice speed control pulse riding the ramp, and the head speed was now correect (no longer running double speed) Finally! But the picture was still totally screwed. It looked like someone twisted the horizontal hold control all the way to one end, but even worse than that.

But I had just been reading that this problem can be caused by severe mistracking. I looked at the head drum tape guides on my new machine and noticed they were both showing about two threads above the adjusting nut. The input guide on mine looked right. But the output guide had the nut riding right at the very top of the post. Then I noticed something odd. There was a spacing washer under the nut which my new deck did not have. I removed the washer and replaced the nut so that two threads were showing. This caused the tape to now ride about 1 mm. higher.

Then I powered up and hit play. And wouldn't you know it, a clear picture popped into view! It took just a tiny tiny tweak of the output guide to totally stabilize it. Now it's absolutely perfect.

So now all I need is to quickly hook up my video digitizing card to the output and copy all my tapes before the thing dies again At least I now have confirmation that my video heads are working. Most remaining VT series machines have bad heads. I have to say that this was the absolutely most difficult restoration project of anything I've ever worked on. But it was also very rewarding. And I couldn't have done it without all the help I got here. Many thanks to everyone who followed along and offered suggestions. And particular thanks to Matthew who was able to create a modern clone of an ancient impossible to find obsolete IC. I ended up needing every one he provided me and they all worked perfectly.

Congrats Michele. VTRs are cantankerous enough even when they're not cutcorner engineered. I remember our VTR guy at Ampex CEPD fuming for days over a single unit, and he had all the parts plus factory training.

Thanks! Now maybe I can finally clear off my workbench for my next project. I'm thinking of taking on my 1968 RCA CTC-24. It would be awesome to watch my Akai tapes on a TV of the same era

Shorten your H-AFC time constant. For noise immunity, sets prior to the advent of video recording had very leisurely AFC response.

Why the devil, after all this time, did staff move this from 'antique television'? VT100 is older than Portacolor, and they never moved those.

Congrats! Double congrats! I am also super thrilled to hear the my FF-10's all worked! Are you going to try to troubleshoot the old servo board now that you have a working one to compare against? I think we would all be curious as to what the original problem was... Also, if I am not mistaken, you now have the parts to three VT-100's. Are you by any chance interested in selling one of them? I would love to own one of these amazing machines. Finally, if you ever need the video amps, just send me the dead one (or the schematic, if it shows what they are made of) and I will be happy to make you a replacement. And, of course, if you ever need more FF-10's, all you have to do is ask - I have lots of boards left.

-Matthew

Yes, actually the plan right now is to first make copies of my old tapes. Once that's done, I do want to go back to the original servo board and figure out once and for all what the devil is wrong with it. As you point out, having a working one for reference should greatly simplify that task. When I gave up on it last time I was futzing with the PUT oscillator.

Once I figure that out, I should be able to get a second deck working. One of the ones I got is actually a VT-100S, which is sort of a deluxe VT-100 with extras like a tape counter and a freeze-frame switch. That still leaves me with two decks. They're not in great shape but I'd be willing to part with them.

In the meantime, I'd definitely like another four FF-10's. I can't believe how many of these I've gone through. Every servo board I tried had at least one bad one on it. And if you can make an LM-1, that would be way cool. That's another high-failure rate part. My 100S has a bad video board and I think it's the same problem there. It's a pretty basic two transistor amplifier, with 4 caps, 4 diodes, and 8 resistors. The VT-100 uses three of these. I'll post the schematic and a photo of the part tomorrow - it's pretty late right now. Thanks!

Here is the Akai LM-1 video amp IC:


The pins are:
Input - pin 2
Output - pin 7
Vcc (+9 v.) - pin 8
Ground - pins 1,3,4,5,6

And this is what it looks like:



I assume that "TAIYO" is the Japanese word for "garbage".

The exact dimensions are 1 1/16" x 5/8" x 1/4". Pin spacing is standard 0.1". Since unlike the FF-10 the pins on the LM-1 are distributed symmetrically, pin 1 has to be marked. The input DC voltage is given as 5.1.

I have it working in simulation. Nice flat response to about 1MHz, 20dB gain.

-Matthew

Wow - that was fast work! I think we need 2 MHz. bandwidth though, as the specs indicate 200 lines of resolution. Or am I computing this wrong?

I did a bit of research on the UJT, just to see if I could come up with a cross reference and what do you know, I did! According to the datasheet at:

http://www.datasheetarchive.com/indexdl ... 102975.pdf

the D13T1 is a standard 2n6027, available everywhere (mouser, for example, has them for $0.37)! I would buy a few and see if that fixes your servo board, once and for all. It is always possible that the replacement UJT got damaged in moving it from one board to another, especially if they are prone to failure.

-Matthew