Otari MTR90 MK II Power Supply problem

[tdstotler]

Hello all. My Otari MTR90 MKII was working fine last night when I noticed the machine stopped. I noticed on the power LED meters that -40 Volt and 24 Volt was out. I had lights on everywhere expect the transport controls on the deck, and I had no transport functions.
Today I removed the power supply out of the deck to see if the problem was there or somewhere else and I still have the same issues. I just spent the last few hours disembling the PSU and am starting to check it out. There is no schematic for this PSU as far as I am aware of, my Otari manuals have nothing in it.
If anyone has worked on these and might be able to guide me to where the issue might be I would be much appreciative. I find it quite off that -40 fails but +40 is working. Since 2 voltages went out at once I dont feel its the power transistors but I will check them anyways.

Todd

 

[tdstotler]

Well after tearing the whole thing apart and testing it, I belive the issues might possibly be in the external transformer.
I followed the issues with the non working -40 voltage back though the power transistors, caps, and made it all the way back to the tranny and there is no voltages there, although there are other working voltages there.
This Otari PSU is rather interesting because the AC line enters the PSU box then returns to the external Tranny, then returns back to the PSU box. There must be 42 connection points on the external Tranny.
I was hoping it would not be something like this, I can replace a cap, switch, bad solder joint, but something on this scale? Damn... Where do I even find one of these bad boys? I guess worse case scenario I can add a second PSU running the 40 volt rails and tap that into the outputs of the PSU. Anyone have any ideas?

 

[bruno2000]

Be SURE that all of the connectors on the circuit boards have plenty of solder on the pins.  We have had several MTR-10 & 12 where after a time, those connections cracked.  I believe our MTR90_II manuals have the PS schematics in them.  I'll go have a look and report.
Bruno2000

 

[gyraf]

Agree.

Also double-check the (somewhat underrated) output connectors on the PSU unit. I've had to service a couple of these.

Jakob E.

 

[tdstotler]

Any PSU schematics would be great, my manual has none of them.

 

[bruno2000]

I have scanned what I have.  PM me with an email to send to.
Bruno2000

 

[tdstotler]

Sent you a PM bruno...

Well I disconnected the caps and checked them and they all seem fine, at least according to my cap tester..

I hate this damn loop back and forth Tranny, really makes it a mess to figure out, but I will get it!

 

[tdstotler]

Sadly I am thinking its the external transformer. My AC voltages are all fine and dandy going into the transformer. One of the 30 Volt voltages that return from the transformer is dead as a door nail. I am afraid they only way I can get a replacement for this is to try to buy a scrapped machine somewhere!!! Rebuilding the transformer is a little beyond my skills.

 

[sintech]

http://www.larkingslist.com/ are currently breaking one, check the Little Bits section. Good luck

 

[fucanay]

I had a MTR-10 that had the same problem. Re-flow all of the solder on the PSU board. I found no less that a dozen bad connections on mine. After reflowing/adding solder on the whole board I never had another problem.

Matt

 

[tdstotler]

But unless I am mistaken, if the transformer output voltage is dead, the fault would lie in the transformer itself and not a pc board correct? Or am I missing something here?

 

[fucanay]

Very possibly, but I thought the transformer was dead on mine as well. I even was trying to source a new one. But depending on where you are testing for voltages, it may still be the PSU board. I was trying to test them on the board where they input and even those connections were screwed. It takes only a little while to inspect that PSU board, if it's anything like the one I had. Worth a shot to check that stuff out since it's free to do so.

Matt

 

[tdstotler]

I will check it out today and resolder the connections, traces. Your talking about the regulator board that pulls in and out, top of the power supply box right?

Thanks buddy.

 

[fucanay]

Well, my experience was on the MTR-10, but yes. It had the PSU down on the bottom of the machine. The top of it was a screen that when removed revealed the PSU board. I just removed all of the connectors, unscrewed the board and turned it over to re-solder everything. And I mean everything. It amazed me how terrible it was under there.

Matt

 

[tdstotler]

Ok I feel like a idiot, when I was checking the transformer I was using my new voltmeter and thought I had it set for AC and you guessed it! It was on DC.

So.... The power transformer seems fine, traced the voltages and I found where its cut out at. Right at the 20Amp -40 Circuit breaker, which
is in the reset positon. This did trip right before the unit went down and I reset it afterwards. There is only voltage on one side of the circuit breaker, all the other circuit breakers have voltages on the top and bottom. So I am guessing the circuit breaker is faulty, but I am going to source a replacement breaker before I go further. I dare not attach a jumper to check the PSU because if that tripped once it could trip again and I could cause more damage, but to my eyes it seems I do have a faulty circuit breaker.

 

[tdstotler]

I am happy to report that I have it fixed and everything seems to be functioning quite well.
After getting a new 20 amp circuit breaker from Mouser, I installed that and then fired the psu up and noticed it kept tripping. So I started from there and disconnected the DC output of the one rectifier, still tripped, disconnected the AC, no trip. So I removed the recitifer in question and replaced it with a new one, and the psu powered up fine, all the voltage lights functioned, checked all the voltages and they were perfect, ran the unit for about a hour, no problem, installed it back into the tape deck, everything seems to work..
I have never ever head a recitifer go bad on me, is this pretty uncommon? I imagine when it went bad it somehow damaged the circuit breaker (the otari circuit breakers are pretty flimsy compared to what I replaced in it).
Thanks to everyone for there help and advice! I greatly appreciate it!

 

[tdstotler]

Let me ask the wise ones on here this question?? While I still have this semi disasembled, would it pay me to go ahead and replace the remaining rectifiers in this baby? The unit is 22 years old.

 

[fucanay]

I have no idea if it should be replaced but good job on fixing this thing. You just saved a bunch of money by replacing a rectifier and a circuit breaker.

 

[W DeMarco]

Nice trace work !!  Not sure if your familiar with Blevins down in Nashville.  He always seems to have Otari parts on hand.  http://www.blevinsaudio.com/parts.html  Hopefully you won't need to contact him.

 

[tdstotler]

Oh yes I know Belvins, I have a MCI 636 so he is a very valuable source of information and parts. I have decided to go ahead
and replace all the rectifiers with new ones while I have it apart. The unit is over 20 years old, it is a very easy swap out to replace them and
I would sleep better at night knowing I have new ones in there.
Yes I was quoted around 5-600 to fix this, so far the cost is $5, with new rectifiers and thermal grease it will be around $25.00.
I LOVE DIY!!!! Also I learn new things everytime I fix something.