Otari smoking (literally....)

Blue Jinn

Blue Jinn

Rider of the ARPocalypse
OK, so on a lark I bought a MX5050BIIB (Ebay...) . Not too expensive. As is, so didn't expect much and figured worst case could use as a parts machine anyway. So, transport doesn't engage at all. It was sort of ff and rew, but not playing at all, and then froze up with just buzzing. Reels were stiff to move by hand even. Finally a pop and puff of smoke from the left reel table. Anyway, suggestions? I am getting a manual with schematics, for the other Otari I have. Figured I'd take it apart and have a look.
 
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Check if the reel-tables got pushed in during shipping.
They shouldn't be stiff and if you tried playmode and reel-motors stuck, the fuse or in worst case motor went dead :(
 
The tables would spin though in FF and REW. (Altenately, and only on one side, so it seems both motors were engaging, with the opposite very tight.) It almost appears as though the breaking mechanism is locked somehow. Before the buzz/pop/smoke, it would play and then slow down and stop. (This was only holding the tape guides, and not with any tape wound.) Wouldn't budge with some tape threaded. I'll look at the tables though, have another exact model to compare with.

I'm wondering if it may be a selenoid. Am I correct in guessing that this would be how the breaks are engaged?
 
The more I look into this, I'm thinking a selonoid. There is a piece connected to a spring on the back of the motor, which connects to a square box. If I hold that up the table spins freely. I took a quick glance at a blow up diagram and it would appear that is a selenoid. So either the selenoid is bad, or the control circuit. However, given the buzzing and the puff of smoke originally in the vicinity of the reel hub, what do you think?

Otherwise the reel table is a little bit off balance as I look at it spinning, but I am not sure if that can either either be compensated for, (assuming I get this thing working) or if it will matter (assuming the wow/flutter isn't too much an issue)
 
Took the cover off. Neither solenoid fires. Also, the motors both turn, at the same speed and in the same direction no matter whether in REW FF or PLAY. So, it's not as easy as the solenoid, it must be electronic now. If anyone can tell me where the motor control circuitry is, maybe it's an obvious problem. I recall a thread here about a small 2pf capacitor going bad, will have to search that thread....
 
Well, found a fuse missing on the main board, replaced that, but no difference. The motors all turn (left clockwise, right counter-clockwise) if play engaged. The right will go if FF/ left if REW. None of the solenoids will engage either. Motors turn at same speed no matter what function engaged, and regardless of the L-H switch setting. (That is they look to be going same speed, eyeballing it.) So more digging...
 
So, got a schematic. Fuse number f701 keeps blowing. This segment provides power to all the solenoids. The fuse is on the 0AC side, there are two "postive" AC's going to a relay prior to the bridge rectifier. This segment of power supply seems to be fairly isolated, the solenoids all connect via a plug and the AC appears (as best I can follow the spaghetti) directly to the transformer. (Don't have that part of the schematic.) Any way, seems to me the fault must be in this pwr supply segment, unless I am missing something. The only other connection to any part of hte main control board is the coil on the relay. Disconnected the connector fo rthe solenoid, fuse blows. Replaced the cap on the other side of the rectifier, fuse blows. The relay seemed to have some leakage in the coil not quite shorts in it but not infinite resistance either. (I am not sure if normal) so going to replace that next and the bridge rectifier. Will keep updating here, but as always, open to suggestions.
 
In case anyone is following this thread. Replaced the bridge rectifier on the pwe supply for the solenoids. They now fire and that seems to have fixed teh transport issue. It was iffy at first, but last few times no problems. Not sure if the relay is sticking in there or not. So for now, seems to be fixed... Having a schematic makes all the difference... Have not tested the deck further yet.
 
Don't know what the smoke was from originally... Hasn't smoked since, and I'm guessing that maybe there was some dust or something, or maybe some friction on the brake. Apparently teh machine had sat for quite some time. Don't know its pedigree at all. Looks really good on the outside however, although some evidence of wear on the heads and lifters.
 
Nice job!!

Solenoids still sticking at all? A lot of them have rubber "cushions" in them to make them quieter and a lot of times those go gooey like pinch rollers and such.

Nice work tracking down the issue...we weren't much help :o but thanks for keeping the thread going. It is valuable info.
 
Thanks for this thread! I have an Otari that I'm just beginning to dive into - mostly preamp issues. For me the learning curve is like climbing a ladder... :D
 
could be caps

if it sat for a long time and smoked after you powered up could just be caps...thats what my teac2300 did, and i replaced a couple of two dollar caps and it runs like new..
 
Don't really know where the smoke came from. The power supply problem was on the other side of the machine, and there do not appear to be any capacitors in the vicinity of the motors. I'm thinking maybe there just was dust or someting on the break felts, or some other piece of dirt that was causing friction because the breaks were on.

The machine seems to have sat idle for quite some time. Most of the switches etc, need to be jiggled a little bit. I have two of these and the other one came with the manual which was invaluable.
 
More followup: Put on a reel of lo-fi jigs and reels, and listened r=through the headphones. 1/4 track playback seems to work OK. Tach is a bit off, so need to check that out, see if something is sticking, (will get tired of counting in FF/REW after about a "30sec" (worth of tape) has gone by...
 
I (ahem) had the tape threaded incorrectly. Tach works fine. Other functions iffy, which seems to be just dirty switches. Has anyone heard of Blue SHower? Can't find deoxit local, just RS branded and Blue Shower.
 
Well, more on this particular Otari. I went ot test out again, and here is something that I just can't figure out:

Seems like every possible adjustment on this thing is out of calibration.

Recorded test tone from on board oscillator. There is a switch to swtith to standard output, based on operating level, or via the output pot. Huge difference on one channel using standard output, but can get to 0VU on playback if manually adjust. OK problem one identified. VRXXX needs adjusting (need that MRL tape....)

Here is what I can't get my head around:

Recorded the tone. RW. Playback, tone is off, so speed is off, have use the pitch adjuster. (Noticed this on playback of some other stuff on teh tape) NOw as far as I can tell though there is only one speed adjust pot. So if it was recording and playing back at the wrong speed it shouldn't matter, on the same machine.

But it would seem as though playback is slighly faster than record, if the tone playbacked different. I could monitor "source" on left and adjust the pitch control for the right just like tuning a synth oscillator....

I can't figure out what would cause this...
 
Wow...

That's...bizarre.

You are right that if the speed of a machine is off you won't hear it if recording and reproducing on that machine...

This is a multispeed machine right? 7.5 and 15ips? There would be a voltage divider or something for the capstan oscillator and I'm wondering if something is screwey with current leakage in different transport modes, but I just can't figure that...I mean...the capstan servo doesn't typically care if you are in PLAY or REC mode...it just knows "go" and "stop"...or actually it just usually knows "go" and the pinch roller does the rest.

So, let me get this straight...you tracked with the speed control on "internal" or whatever, and when you reproduce against the tone oscillator you can hear that the oscialltor output and the tone reproduced off tape are "out of tune" and you have to use the pitch control to get the reproduced tone to match the oscillator output??
 
sweetbeats said:
Wow...

That's...bizarre.
Click to expand...

I agree.

This is a multispeed machine right? 7.5 and 15ips? There would be a voltage divider or something for the capstan oscillator and I'm wondering if something is screwey with current leakage in different transport modes, but I just can't figure that...I mean...the capstan servo doesn't typically care if you are in PLAY or REC mode...it just knows "go" and "stop"...or actually it just usually knows "go" and the pinch roller does the rest.
Click to expand...

It is actually 3 speed 3.75, 7.5 and 15, there is an internal switch to choose between two sets of them, and then trimmers for the three. But you're right, I don't see sep speed adjustments for "REC" vs "PLAY" just the three speeds, the capstan should just go or not go.

So, let me get this straight...you tracked with the speed control on "internal" or whatever, and when you reproduce against the tone oscillator you can hear that the oscialltor output and the tone reproduced off tape are "out of tune" and you have to use the pitch control to get the reproduced tone to match the oscillator output??
Click to expand...

Yeah, exactly. I could actually tell from listening (I'm that good :) ) that the pitch was off. So I monitored "source" on left and "tape" on right and could hear the difference, so I adjusted the pitch control down to "tune" the playback.

Yup. It's weird. The tape is Quantegy 031 white box, but Quantegy not Ampex, (AFAIK, it all came in a Quantegy box, but nothing is sealed with the white box stuff) so no sticky tape issue. This AM I just ran some tape through it on play to just let the motors work a little, on the assumption that maybe, just maybe, the capstan was sticking for some reason on record.

Now that I think of it, a song that I had recorded on that same reel to align a Dolby unit w/ the other Otari sounded like it was playing back slower. So maybe there is a problem wtih teh capstan motor or motor control. The thing is it didn't sound like it was drifting. The tone (20 seconds worth) was steady.

So tonight I think I'll just record a full tape of tone, and see if playback wavers at all.

:confused:
 
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