Technics RS-AZ6 cassette deck head replacement

[shakalnokturn]

I bought this tape deck to repair, not cheap enough it seems.

Original symptoms were that counter was not counting and operation stopped as soon as keys were released. It sounded easy enough to take a gamble.

That was soon fixed, it was a shorted electrolytic on the supply to the reflective IR sensors.

Then I had the bonus that the tape was drifting outwards and getting folded due to a bad pinch roller but I had spares around...

After that it played great.

The record test was a fail though. Right channel was very low and both were lacking in treble.

It's a nice 3 head model with magnetoresistive play head that's quite unique to the RS-AZ6 and RS-AZ7 decks that weren't produced very long.

The record head has a nice wear groove in it to explain the poor recordings. Unfortunately a good head assembly looks unobtainium.
The magnetic record head and magnetoresistive play heads are glued into and onto a common support.


Not having much to loose (other than the risk of damaging the play head) I thought I'd try replacing the useless original record head only, knowing that alignment with the play head was going to be much fun...
Going through my stash I found a play-only auto-reverse transport that had a small enough head to fit in the Technics AZ head assembly.

Next step was removing both heads by heating them with the soldering iron enough to soften the surrounding glue, then pushing them out of place, cleaning the glue off the salvaged head and AZ assembly recess.

AZ assembly has a small spring clip that lightly holds the head in place so I loosely fitted the replacement head, readjusted the play azimuth then did a record test at 10kHz while monitoring through the play head.
Fiddling with the record head position I was able to get same levels on both channels although most of the time right was lower than left, frequency response was good but record level was much too low even with record level at maximum.

I'll have to scope to check that the L/R heads are actually getting similar input, the deck has few trimmer adjustments, according to service manual the CPU does most adjustments automatically so I'm not sure how I'd go about correcting if there was an imbalance.

Anyway, rec level too low, something is wrong... took the replacement head back out and compared it to the original with the "transistor tester" (TM).

Original head (blue):
Left:   68 / 4.5mH
Right: 71 /3.4mH

Replacement head (black):
Left: 214  / 63mH
Right : 235  / 61mH


Wow! Such a difference! I'm sure that could be a reason for the low recording level.

The deck uses an AN7356 to drive the Rec. heads. How would I go about getting it to output sufficient levels considering that the level meter is around -10dB on playback while recording is at maxed out (in the red)?

A couple extra questions:
Could the differences in inductance between L/R on heads be due to the wear, or more to the proximity of the metal encapsulation?
Anyone know the use of the small flathead screw on the side of the heads? Used during manufacturing I guess... Slant adjustment? Gap adjustment?

[shakalnokturn]

Service manual.

[commongrounder]

That head has many hours on it! If the assembly proves to be truly unobtainable, there may be just enough left on the worn head to explore relapping. Record-only heads can get away with wider gaps, due to how the magnetic flux is generated. The gaps on your example seem to be (visually) similar to each other, which is good.  The big question is how many more hours you would get before the head is truly finished off, and whether that would be worth the cost of lapping.  Back in the day, when a head was that worn, I’d just replace it without a second thought. Your replacement head is definitely not electrically compatible with the record circuitry. The drive will not be adequate for proper bias and audio. At the very least, you’ll have a good playback machine. Best of luck!