Otari FET Packs (MX70)

[Dreams]

Otari Part No. I-0053

Potted 7-pin SIP

Anyone know if these are available anywhere?

There are 10 of them on each audio card, and a bunch of mine have gone bad. Somehow...

It looks like they're just series-shunt jfet mutes used for switching.

I'll post an image of the circuit.

I first noticed the problem with these when monitoring the repro head; the input signal could clearly be heard just before the delayed signal from off tape. I've got a whole set of spare cards from a parts deck, but eventually that well will run dry, and some that I've pulled from there are showing the same problems. Makes me think that there are more of these causing other less obvious problems.

My first thought was buy all new ones. My second thought was de-solder them all and test each one in a test jig. My third thought was just say forget it and throw some new J111s at it. Thoughts on my thoughts?

Sorry about the terrible picture quality....

 

[plimousse]

Hello,
Please try : http://www.audioproz.com
Cheers,
Pascal

 

[Monte McGuire]

I used to have an MX-70, and none of these ever failed. A few output amplifiers failed on the previous owner's watch, but nothing else ever failed. Maybe check the power supply voltages before you send more hybrids into the abyss? ;-)

 

[Dreams]

I used to have an MX-70, and none of these ever failed. A few output amplifiers failed on the previous owner's watch, but nothing else ever failed. Maybe check the power supply voltages before you send more hybrids into the abyss? ;-)

That was the first thing I did. Everything looked ok; voltages were pretty on and ripple looked fine.

I wouldnt say that they "failed" as such. Offness was pretty seriously degraded though.

I've not really run into that kinda thing before. I've seen dead fets on other gear, sure, but not leaky like this.

 

[Dreams]

Speaking of those output drivers, anyone have any experience with these:

http://www.recordingservicesandsupply.com/item/otari/output-driver-replacement-for-/lid=44716247

Maybe Brian Roth would like to comment?

 

[Brian Roth]

Interesting that someone would ask (I didn't want to "pimp" my own gizmo!)

Last spring, a friend/client brought me his MX-80 24 track which had been stored away for several years.  It had a few misc. problems (like the AC mains inrush relay circuit) but otherwise ran well.

BUT, I quickly discovered that ten (!!) of the balanced line outs were dead, usually with a large DC offset voltage on XLR pins 2 or 3.  The current Otari rep here in the USA only had 7 in stock at something like $110 apiece.  So, I breadboarded a perfboard proto for proof on concept, then laid out a circuit board.

Even though the output hybrids were the newest version, they still had failed.  Later conversations with an ex-Otari support engineer revealed even that version had problems with certain batches.  Interestingly, 9 of the 10 bad output hybrids had separated from their aluminum heatsinks.....


Bri

 

[Dreams]

Hey Brian, thanks for the reply.

I've seen two different revisions of the I-0178; the "A" and the "B".

Seems they just couldn't get them right, for whatever reason.

A few of our "B" versions failed, and we're currently working our way through the parts machine cards which have the "A" version drivers.

I wouldn't be surprised if we placed an order for a few of your replacements in the next year. Good to know they exist.

What do you think about making replacements for the FET packs?