(This text was revised in August 2018.)
One of the decks I lusted for in my early teens, but could only dream of, was the TEAC V-1RX. Having read on www.tapeheads.net that it is a good one, I stumbled over an ad for one in the Netherlands. Not cheap, but allegedly recently serviced with all new rubberware (or was it rubberwear?). I bit, and days later I was the proud owner of another ... problem case (photo above is not mine).
The V1-RX is unique in the single-number V series in that it is the only one with a direct drive (single capstan), and solenoid-less transport operation. Being DD not too much can go wrong with the mechanism, or so they say. There is one belt, for the control motor, and then two idler wheels for the tape reels. Upon testing my deck made awful howling noises inside, both while playing and while winding. Winding was slow, and playback was with a juddery takeup reel. Pots and switches were crackly. The dbx was totally malfunctioning. And here I was, thinking that this one would be a low-effort addition to the collection...
Upon opening I found the control belt in good health, but the idlers looked funny and clearly were impeded in their motion, or the idlers themselves where impeding the motion, that was not clear. There is no V-1RX service manual available on www.hifiengine.com, and its unique build make the manuals of its V-2,3,4 and 5RX siblings not very useful, but after long and hard looking I found that the transport section of the Tascam 122MkII was mostly identical. And see what is occasionally offered on ebay.fr!!! https://www.ebay.fr/itm/Idler-Tire-Belt-Rubber-Zwischenrad-Gummi-fur-TEAC-122MKII-Cassette-Tape-Deck/282833205599?hash=item41da2c395f:g:N~kAAOSwk~ZZ-KA~
There are a few forum threads that discuss repairing the V-1RX transport, so I won't go into total detail myself. Just visit http://audiokarma.org/forums/index.php?threads/teac-v-1rx-two-questions.464953/, http://forum.vintage-audio-laser.com/resolution-pannes/remise-etat-une-platine-cassette-teac-1rx-t7708.html, and http://www.tapeheads.net/showthread.php?t=51930. The reel motor assembly with the idlers is removed easily: two screws and lifting out. No need to move the transport itself.
The two idler tires I found in there were simply too large (see picture below), and were pushing against the motor axle and the reel hubs all the time. Small wonder this didn't work smoothly. Off with the old ones, on with the new ones. But wait ... this didn't go easy. After much finicking (don't let the small spring in the idler assembly jump free and fall into the cassette well, for instance ... yeah, I know) I had the tires on their small plastic wheels. But they were not sitting well there, with their run surfaces not quite parallel to the reel tables. Presumably the inner diameter of these tires was slightly too small, putting strain on them once mounted, causing deformation. I tried and tried, until I realised that if the plastic wheels broke during all this trying it would be game over for the deck. So I gave up and used the transport as is. This worked better than before, with reasonable winding and not too much noises. But far from silent.
A lot later I got fed up with this. Ordered a fresh set of 122MkII tires, only to find that they were actually quite obviously too small. The necessary dimensions are ID=13.5, OD=19, D=2.5 mm. What to do? Well ... I went back to the original oversized tires. I thinned them on a sheet of sanding paper to 2.4 mm, and I carefully reduced their OD to 20 mm. I heated them for a while in the sun, and then they went on easily. That made the transport much quieter. Wow & flutter, measured with TEAC MTT-211NA, was less than 0.035% weighted RMS. The best-performing transport in my harem.
In the meanwhile I had found a circuit diagram, now you can have it from HE: https://www.hifiengine.com/manual_library/teac/v-1rx.shtml. I replaced most of the electrolytic capacitors in the power supply and in the audio circuits with my usual Panasonic FCs, Elna Silmics, or Nichicon Muse bipolars. Pots were sprayed, switches were worked tens or hundreds of times (the front panel switches are very hard to reach. Getting the front off is easy, getting it back on again is all but easy!) I also changed the power tranformer wiring from 220V to 240V. Euro has moved up to 230V, and the deck has some rare and hard to replace lamps running off AC, so these better receive the least stress possible. The pictures are from after the work was done. (Does anyone know why Japanese consumer electronics PCBs are always stuffed with all capacitors askew?)
Playback from the TEAC MTT-356 tape was a downer. 6dB of treble loss in the right channel, and 4dB left. I began to fear for a worn head, even though it looked OK, and wasn't even very dirty when it came in.
I didn't try record/playback in this raw state, but opted for a crude alignment first. Contrary to all Nakamichis even this top-line TEAC is rather lacking in the alignment settings department. There is per channel variable capacitance for type IV bias, then a mono variable resistor for type II bias and one for type I bias. Bias for I and II are not independent: both derive from the type IV setting, so re-aligning metal forces you to always re-align I and II too!
I used a Sony Metal XR (1992) and set bias by minimising the distortion of a 400Hz 0dB (200nWb/m ANSI) tone. These are the resulting -20dB frequency responses, top without Dolby B, bottom with (ignore the legends, they are not related):
The next plot is for a Maxell UR (1994). The good news is that it reaches 19kHz, allaying all fear of a worn head.
What then of that significant treble loss on playback? The -2dB at 10kHz and -4 to -6dB at 14kHz actually match the calculated loss for a 10' azimuth error rather well:
Recording test tones and white noise and playing them back on my Cassette Deck 1 with its azimuth control confirm that the TEAC's azimuth was indeed off a bit. I subsequently reset the azimuth, first with the A.N.T.Audio 10kHz A100 tape (http://www.ant-audio.co.uk/index.php?cat=post&qry=alignment_tapes), then followed with fine tuning by means of the MTT-356's 12.5kHz section. For this I had to loosen the azimuth screw first, using nail polish remover. I used a non-magnetic screwdriver. After the operation I secured the screw again with bright-red nail polish.
What followed was a period of repeated measurements with the MTT-356, with a lot of frustration because of aberrant treble levels (today too high, tomorrow too low) and inexplicable channel imbalances. I tried adding capacitive loading to the head. I tried brute-force additional equalisation in the PB amplifier, all to no avail.
What did it in the end was a regime of cleaning and polishing the heads thoroughly, with Brasso and IPA, and then again. And then once more. That yielded this:
Very acceptable. Left sitting below right in the bass is normal for a full track tape. The mids are a bit low overall, but this is probably not abnormal for a deck of that era. This could be redressed by slightly changing the main timeconstant in the PB amplifier, for both channels equally. As built this is 130 us, maybe 140 or 150 us would be a better choice. This can be done by substituting 14k or 15k for R105. (Note: theoretically it should be 120 us, but as heads are imperfect and have losses, it should be more than 120 in any real-life deck.)
I took 15k, ending with this playback curve:
TEAC V-1RX restoration Part 2
