MX 5050 no Rew or FF

technoplayer

Recovering Gear-aholic
I acquired an Otari MX 5050 b-II and an MTR 10. I planned to use the 5050 to replace my Tascem 35-2 as the Otari has the added lower speed which I need. The 5050 is clean, and records/ plays/ functions fine except it will not rewind or fast forward. Mechnically the solenoids, motors, brakes, etc function fine in the play mode , so i am now looking at a potential electronics issue.

All the plugs and fuses check out. Only odd thing I can find in that capactor C 801 on the main rear board (the on that hinges out) is not there. It looks like it MIGHT have been at one time, but..???

Can anyone with a 5050 b-II confirm if this cap is present in their machines? it is one of the large vertical electrolytics.

And a link to the schematics would be really helpful
 

Blue Jinn

Rider of the ARPocalypse
I had some pwr supply problems on this board as well. This board supplies pwr to the solenoids and motor control circuits and relays. Are you positive the fuses are all good?

I'm still scouring the schematic for C801. Give me a few more days.
 

technoplayer

Recovering Gear-aholic
Thanks Jinn!!

I only did a good visual chack on the fuses, but i did not pull them and do a continuity check. But I will...

That C801 is a fairly large capacitor on the lower left corner of the board (when in the down position)

The messed up thing is that it plays and records fine...the reel motors and capstan motor operate fine, the reel brakes engage and disengage as they should in the play mode, the pinch roller solenoid engages fine, etc. That is to say MECHANICALLY it seems to function as it should....EXCEPT the rewind and fast forward buttons are non-functional dead. I traced the wires from the switch to the circuit board, unplugged it, and tested for switch funcation at the plug. It reads that the switches work fine. The contact closure signal is getting "lost" somewhere before it gets to the place where it should A: confirm the brakes are released and capstan solenoid is disengaged and B: corrently powers the reel motors for either FF or REW motors as selected.

Just to narrow things down, is the large swing out board in the rear the one that has the transport control functions on it?
 

technoplayer

Recovering Gear-aholic
UPDATE TIME.

So last night I'm walking by the 5050, so I just randomly turn it on hit FF and
THE DAMN THING WORKS.....for about five minutes anyway, fast foward and rewind worked perfect.....

Than thay stopped working again. Gremlins

What makes me VERY optimistic now is that in my mind it confirms the electroncs are solid and complete. I suspect this narrows it down to an electromechanical issue, possibly a sticky relay. Since i do not have schematics on this unit, a relay problem is an easier one to solve cause I KNOW what those look like.

Anybody else have an opinion here??
 

Blue Jinn

Rider of the ARPocalypse
Sounds like it could be a sticky relay. This is a 5050BII correct? I have a schematic, but haven't been able to trace where the FF/RW relays engage. Also, I've done a fair bit of research into replacement relays and am reasonably certain the Omran G5LB is equiv. I also have an NTE part number around here somewhere. I'll post again when I find that relay. I actually have it (the relay) lying around here somewhere.
 

technoplayer

Recovering Gear-aholic
Thanks Jinn.

yes, Its a MX 5050B-II-2

I tried some manual checks this weekend.
>> Unplugged and replugged every connector internally to check for loose connectiosn (again) and break up any potential oxidation
>> Flipped out the rear circuit board, which contains most of those Omron relays. They all seem to actuate when the play function is enabled, which is not surprising. I would expect separate relays for each reel brake solenoid, each reel motor, and the capstan. What gets me is why the reel motors and brakes would work in the play mode and not FF/ REW

The relays are all the same, and are very easy to get to and replace.
Still in a fog as to why they started working..then stopped
 

technoplayer

Recovering Gear-aholic
NOTHING happens when FF or rewind is pressed. No reel motor power, no brake release, NADA.

Everything behaves properly in play and record mode at both speeds. The brakes release and the reel motor spin and etc. It's just FF and REW that are totally non-functional. (except for one 10 minute period one day last week when EVERYTHING worked fine). I would think if was power supply related it would either always work or never work.
 

westgate

ɹǝʎɐld ɹǝpuǝ&#6
NOTHING happens when FF or rewind is pressed. No reel motor power, no brake release, NADA.

Everything behaves properly in play and record mode at both speeds. The brakes release and the reel motor spin and etc. It's just FF and REW that are totally non-functional. (except for one 10 minute period one day last week when EVERYTHING worked fine). I would think if was power supply related it would either always work or never work.
i think 'tech-repair-experience wise', you're lightyears ahead of me but would a squirt or two of deoxit in the ff/rw switch mechs help at all?
seems to work for similar situtions on a few of my consumer decks.
good luck!

edit-i do see where you say the signal is getting past the switch, tho. it's a toughie.
 

technoplayer

Recovering Gear-aholic
Thanks...yeah, I de-ox'ed all the switches and pots first off, as typically something is going to be scratchy or intermittant on a vintage machine. . That goes for doing a un-plug and replug on every connector and edge connector.
Clean and lube, check all the rubber parts for stickys, clean clean clean,
etc.

My next pass will be to turn it on and run it in play mode all day. (play flip play flip since no rewind) ....maybe if it warms up it will behave different.

I conclude at this poiont that somehow the switch closure signal from the REW and FF switches is not getting to the relay energize circuit. Maybe a capacitor in the latch up circuit??
 

Blue Jinn

Rider of the ARPocalypse
The schematic I have is way to big to easily scan.

Looks like the momentary switches are pwr by -21v which then causes the +5 cv to go to the IC605 (BA843). (If I'm following this correctly.) There should be a control voltage at points 12 15 & 18 on board PB-46Q. (Rec/Rew/FF respectively). These three switches share a common pwr source point 82-3 pwrd by (apparently) -21v at point 82-2 with the EDIT in normal mode. This voltage goes to a resistor and 7414 and 7403 (as best I can tell it isn't labeled). The top of the resistor indicates +5v, so I'm assuming (again, I got my BSEE out of a cracker jack box....) this is the voltage sent to IC605 which in turn sends a cv to the base of Q604 and then to RL 601 (FF) or Q605 & then to RL 602 (rew). I'm assuming the cv on the base of Q604/605 causes it to conduct thence operating the relay. (grounded emitter) Check for voltage on the base of Q604/605 when either is engaged and pins 15 and 13 of the IC. Here is the datasheet for IC605 (BA843)

http://www.datasheet4u.com/download.php?id=543673

I can't seem to resize the relay data to fit and still have it readable. The NTE part number is R46.


Let me know if this helps. I'll look some more. I am pretty swamped right now so I don't have the time to open my machine and poke around.
 
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Blue Jinn

Rider of the ARPocalypse
Any progress? BTW my Otari now has the right channel not recording or playing back properly. Still identifying the problem...
 

slowmotion

New member
Could be just a dried out/blown motor run cap. I had one in an Akai RTR and it would play and record fine but not work with any of the higher speed functions. Replaced it and it works just fine. Not the motor START cap (which will most likely be pretty hefty), but the motor run cap, which will be a bit smaller, but still pretty much wired directly to the motor somewhere.

Just a thought.
 

technoplayer

Recovering Gear-aholic
Not much to report. The day job went into overdrive and I haven't seen the inside of my studio in weeks. Where I was at before the dam break:

>> It plays fine on both speeds, brakes release, tension is good.

>> ONE TIME when I powered it up it worked perfect for about ten minutes, which in my mind excludes totally blown or missing components

>> I have done the de-oxit treatment on all pots and switches

>> I have continuity on the FF and REW switches back to the PCBS, so its not a switch malfunction. Anyway, it would be hard to imagine both would go flat at the same time.

>> I have cross referenced that IC605...it is called a tape key controller, basically a simpe logic IC that translated the key closures to the tape deck logic circuits. The original ROHM IC is un-obtainable, but there is a Mitsubishi M54410P that is a drop in replacement. Not saying thats the problem, but its the prime component in deciding which key closures will send signals to the transport control electronics. Once i get in there with a VOM and scope I will be able to see if the IC605 is passing the signal along.

Sigh....where does Sweetbeats get the time......
 
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