Ampex VR-1200 2″ quad VTR restoration

photo of VTR

A log of what's happened, so far.  Pictures are clickable to view larger versions.  The yellow tag above circuit breakers marks the one that popped out (once).  I forgot to jot down which one it is, so I'll have to update that information, later on.

A few people have had a look at this machine before I did, and still are, but I haven't asked if they mind being named, so I won't.  I think the first time I saw this machine running (trying to work) was when the owner had group of retired engineers drop by for a demo of various one-inch and two-inch machines, and one of my Philips LDK2 cameras, and one of the visitors just couldn't resist diving in and trying to fix it up as much as he could manage at the time.

There was an auto-servo to control the head penetration on the machine, but it would only alternate between too much and too little, at the two extremes, with no in-between positions.  So the servo was removed, long before my involvement, and a manually adjusted head block installed.

31 Oct 2011

photo of screen photo of screen photo of screen
CRO traces are “RF dub” output above “SWR RF OUT” (waveform monitor output).  First pic drop-out-compensator off, second and third DOC on.

October/November 2011, machine's first observed behaviour:  Scrambled picture, with appearance of some picture buried inside noise, but looking like the horizontal scan rate off frequency (interestingly, proc amp controls adjust right parts of picture—sync and picture gain and black levels, correctly and independently).  Tracking meter low/no output, tracking control ineffective.  RF playback dropouts (used CRO on RF dub output terminal).  Characteristic whine of quad heads sounded not quite the same pitch as I expected.  Signal doesn't make it through the full E-E path through machine, black lines across picture (some asynchronous addition of sync on top of the picture).  Monitor switcher has distorted output (intermittently had async sync drifting through picture, and white crushing).  There are two simultaneous outputs from this switcher, one okay (SWR OUT), the other distorted (the picture monitor video output).  Separate socket for sync to waveform monitor has a very low output level.  Various test points in left hand rack units have no outputs.

All cards in mod/demod and servo racks down the left side pulled and contacts cleaned, no change observed.  Pulled out video out/in leads between modules, and inserted colour bars.  If replace DEMOD out from left hand rack units with colour bars, get a good clean picture on main output.  Suggests AMTEC and COLOURTEC modules are probably okay.

photo of vectorscope photo of vectorscope photo of vectorscope
DEMOD out, COLORTEC out, main video out, in E-E mode, with progressing chroma instabilities

E-E restored:  A coax wire had broken in the (module 5) board for the RF-dub/RF-mod input selector.

Black lines over the picture can now be easily seen.  Appears to be asynchronous sync over the picture.  Careful poking of finger over back of traces on sync processing board (12) around trimpots showed R74 changes the frequency.  Playing with R74 can change their frequency to match the picture, but they're still out of phase (locked on frequency, but wrong position, horizontally).  Width of pulse looks more like blanking pulses, rather than sync pulses.  Temperature/time dependent, needs re-tweaking often.  Yes, I know you don't “fix” things by playing with trimpots, but it's probably been fiddled with before, will need fiddling with again, and I know I'll have to look at the circuitry around that trimpot to find the fault.

photo of screen photo of screen
Black lines over picture

Control head cleaned, properly.  The wrong side was being cleaned before (the shell of the head, not the side that faces the tape).  Tracking meter, now, shows a reading (about 1/3 deflection).  Haven't checked whether that's a fluke, yet (dunno whether the tracking meter shows control track output, or head RF output level).

Tried changing video head, saw no observable difference to picture.  Moments later, smelled smoke and a circuit breaker had popped.  Unable to locate actual source of smoke, nor see any apparent damage.  Smell most strongly around top left of mod/demod rack, or erase head module behind front panel.  Didn't see any change in behaviour when happened, we manually shut off power the moment we smelt smoke, noticed the breaker had popped afterwards.  Breaker unrelated to those functions, can't remember what it was, but marked it on the panel.  Replaced original head, playback same as ever.  Later on, swapped heads, again, playback same as ever.  Swapped back to original heads.  No further smoke smells, or breakers popping.  Not sure if something merely got hot, or actually burnt. 

High-band/low-band mode switch very unreliable, but working normally after sprayed with contact cleaner and switch rotated a few times.

Extensive cleaning of tape path, and internals of capstan motor.  Got a near-normal monochrome playback picture, from a monochrome recording, when machine warmed up.  Before that happened, was playing back with appearance of tv set with horizontal hold slightly off frequency (diagonalised picture, sync locked but off frequency), gradually getting closer to correct rate over time.  Interestingly, doesn't appear to have any of the common quad playback errors (16 line segmented or scalloped picture).  Tracking meter is reading a steady value, tracking controls have no effect (to picture, nor can we hear the servos do anything).  Machine appears to be free-running tape speed-wise and head speed-wise.   Minor tweaks of speed controls on servo boards can make the machine drift onto frequency, but it will not lock, behaving like a tape recorded with no control track.  With very fine speed adjustment, can move noise bar to bottom of picture, and see minimum of skew error, but can't get a noise-free picture.

photo of screen photo of screen photo of screen
Playback beginning to work (late 1960's Adelaide television)

Really unreliable audio level pots, for input and output, cue and normal audio.

+135 volt supply is at 150 volts, at the front panel test point.  And the +24 volt supply at 25 volts.

More to follow… But really need manuals, and someone experienced with servicing these machines.


Later, someone else fixed the +135 supply, bridging together two pins in the supply (on its rear-panel connector, where it plugs into the rack).  Apparently the supply was missing a ground reference.

They temporarily blocked off the signal creating the black line across the picture, and we could see a reasonably good looking picture.  And they replaced a bad transistor on the same board.

The horz phase and stability controls now do something.  I could adjust the wild instabilities out of the picture, and I could adjust the phase until a vertical row of white dots (head switching noise), shifted into the front porch of the horizontal blanking period.

We tried connecting the VTR through an external TBC, to see if that could give us a stable signal, and I'd say it was only slightly better.  It was connected to the demod output, to get a minimally processed signal.  Disconnecting the demod from the amtec upset the servos, so we fed the demod into a distribution amplifier, and the outputs of it to the amtec and the TBC.

There's still a small horizontal shift on the first line from each head, after the switch.  Playing with the tip penetration and scalloping controls don't remove it, and neither did the external TBC.

The internal sync oscillators seem to be always way off.  I don't have circuit notes to know where they are, or how they're done (L/C, crystal locked, or something else).  Switching playback to internal sync mode makes some very noticeable changes to video scan rates, and motor noises, compared to being locked to an external, on-frequency, SPG.  I don't know if the machine is supposed to be able to play off the internal syncs, or if it's just a test option.

Putting colour bars through in EE mode, has some rather horrible looking interference patterns in low-band mode (I'm guessing low band was pre-colour era), which mostly go away in high-band, but not completely.  Though we are missing one of the colour boards, slot 15 is empty, so I suspect that has a lot to do with it.  Also, the EE button lights up and lights out, but doesn't appear to do anything else (whether the machine is stopped, or in playback).  My EE observations on this page are from when the VTR has been stopped.

It doesn't want to actually record.  I saw it once go through the motions, but not record anything, the tape was just full of noise when played back.  Since then, every attempt to record just results in a relay buzzing from the box of relays on the back panel, and no reel motion.  While we have no real need to make recordings, it'd be nice to get that working.  And it gives you a way to make another test tape, rather than risk losing a recording you'd like to keep, if it mangles the tape.

10 Jan 2012

We could have left the signal blocked off, but did want to see if we could get it working properly.  I went through the board with a CRO, comparing the circuit to the diagram of same board as found in the VR-2000, making some presumptions about the signals I'd expect to find through the board, and adjusting the trimpots for the what I'd expect the normal signals to be.

On the sync processing board (12), I could adjust VR74 to get the black line to stay locked in front-porch area.  But now we had a narrower than normal horizontal sync, and a very narrow pulse just before it, giving us an interrupted horizontal sync.  I could adjust another trimpot to widen the front porch pulse, and another to widen the blanking.

Early 2014

Popping circuit breakers, then chaotic playback speeds.  One of the tags in the 12 volt power supply modules went very dry jointed, looking like the wires on it had never even been soldered together, then one of the shunt regulator transistors went short circuit, leaving no negative 12 volt supply.  Intersync chassis board 6 (I think, from memory), is going wonky and not properly switching between NTSC and PAL speeds for the head drum (the NTSC speed control is affecting PAL playback speeds, too), and it seems more like it's free-running rather than locking onto the correct speed.

Sync processing board 12 is still going crazy.

Actually got the machine to go into record mode, for the second time, ever, though the results were horrible (very low signal level, one head much worse than the others, and quite distorted).  I had poked around with a stuck microswitch under the supply reel, which appeared to be a record-lock-out switch, according to part of a manual.  Quite how it was supposed to work, I don't know, as above it is a moving reel, which would stuff up such a switch, and there's quite a gap between the switch and the reel, so they'd never be able to touch.  I could only guess that a weighted ring might be placed over the hub, but there's no apparent mounting holes to hold anything in place.

Previously, it had once gone into record, though only seemed to erase, them promptly emitted a burning smell from a mystery location, then popped a breaker, but we couldn't find anything burnt.  Subsequent attempts just resulted in chattering relays, or acting as if no buttons had been pressed, at all.

The 1200 had decided to let something fail in the head speed control board.  The electronic switch that controls whether it was running NTSC or PAL failed, so the two tape speed trimpots became interactive.  And another servo loop is failing, so it's freewheeling near speed, rather than locking into sync.

At this stage, the VR1200 has been giving us so much grief, that we decided to finally get around to trying to modify the AVR2 to play back low-band tapes (we don't have the optional low-band modules to swap in, but did have spare high-band modules to modify).  And we succeeded.


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