MCI JH-16 Low Frequency Oscillating Same Speed as Capstan

[Scrappersa]

I posted this over on the MCI forums, but they're not really active. I was hoping that some people here may know where to look to figure this out. I've been having a problem with my machine, where certain tracks have a low frequency oscillating sound. It only happens in the first drawer. What I've noticed, is that when I move the black power cable that runs from the power supply to the actual drawer, it switches the channels that the oscillating is happening on, and sometimes even the loudness. But it's not something that happens immediately. I've tried rearranging all of the cables that run to the drawer and pulling the power cable out of the way. It's caused it to be quieter but it is still a problem especially in quiet songs. The thing is that it tends to happen at the speed of the capstan motor. I just placed an order on mouser and bought enough capacitors to recap both power supplies (except in the audio supply the four 3100uf 75v + caps), the capstan tach board, the phase lock loop board, analog torque board, the logic board, and the motherboard.  I did notice that on the motherboard, C1 4.7uf 35v, a tantalum cap looks to be blown out. Has anybody heard of this problem before?

 

[Biasrocks]

Recapping is a good start. If you do the math, those original caps are 25+ years old.

After you recap, I'd suggest doing a FULL alignment and then retest.

Do you have a scope? That can help track down the source of problems.

The MCI forum (http://mcirecording.com/forum) has been a reliable source of troubleshooting ideas with lot's of guys dealing with these machines for years. I see you posted your question over there about 2 hours ago, seems a wee bit unreasonable to get an immediate response. If you do need that, contact Steve Sadler who will diagnose problems over the phone with you. He has a diagnostic service which you can subscribe too which is well worth the price of admission.

Steve's contact: 615-242-0599
[email protected]

Got an '87 JH24 here, running and sounding great.

Regards,
Mark

 

[Scrappersa]

Thanks Mark. I have Steve Sadler's service. He is absolutely amazing, but we have not been able to uncover this problem as of yet. I figured maybe somebody else has had the same problem. I just did a full alignment about two weeks ago.

 

[echo zulu]

The problem you are describing sounds like a bad connection. Before diving into a recap, I would check the 3 multi-pin Jones plugs and connectors on top of the audio power supply. Make sure all the connections are clean.

If you have already done that and still have the noise, there could be an intermittent connection in the suspect drawer's cable. Check continuity at both ends with a DVM while moving the cable around (unplug the machine first!).

 

[Scrappersa]

Hey Echo, I checked the plugs on top of the audio psu and they are fine. I am constantly cleaning all of my molex connectors and it definitely helps. I also did a recap of both power supplies. The problem is still there.

I disconnected the master channel strip board from the first drawer so that nothing would be in the audio path. When I ran channel 4 into my Fireface 400, I still heard that weird oscillating sound. I then took channel 4 and plugged it into my Behringer ADA8000 that is adat into the Fireface, the oscillating went away. I cannot for the life of me figure out what the problem is. It seems like it would be a weird grounding issue of some kind since it disappears when it is in the Behringer, but I had the same problem when I used to run it into a Soundcraft Spirit and a Motu. It looks like the Behringer may be unbalanced line inputs. I've tried rewiring the cable to pin 2 hot, pin 1 hot, pin 3 hot and any combination I can come up with, but it seems like my tape machine does not like most interfaces.

Any ideas?

 

[Biasrocks]

Have you checked that the pinch roller is in good condition? I put a Athan on mine when I got it and that solved some problems I was having with the original PR.

What about the capstan bearings?

Regards,
Mark

 

[Scrappersa]

The pinch roller feels like it's in good condition. I have two different pinch rollers.

I think that the capstan bearings are in good condition. The motor is pretty quiet overall. Is there something that indicates bad motor bearings that I can look out for?

 

[Biasrocks]

The pinch roller feels like it's in good condition. I have two different pinch rollers.

Are the symptoms the same if you change the pinch roller?

I think that the capstan bearings are in good condition. The motor is pretty quiet overall. Is there something that indicates bad motor bearings that I can look out for?

Grinding, weird noises, uneven operation of the capstan.

Do you have a scope, perhaps you could look at the capstan/motor control signals to see if they're clean and as expected.

Have you completely demagnetized the tape path?

Also, David Blackmer has some good tips on MCI's.

I've done almost all the mods he suggests on my machine.

http://www.blackmerdesign.com/?page_id=404

Regards,
Mark

 

[Scrappersa]

Thanks for the link. It was an interesting read.

The symptoms are the same when I change the pinch roller.

The capstan is pretty quiet and the tape path seems to be even and consistent. I haven't had any problems with recording, erasing, or playback other than on the channels that have this sound.

I have demagnetized the entire tape path including all of the metal guides.

 

[Scrappersa]

I took the pinch roller off and let the machine run without it. The sound was still there but what I noticed is that it actually happens at the same speed as the reel motors. I really wonder what is going on with it.

For anybody who isn't familiar with these machines, the yellow and red molex connector is connected directly to the output and input xlr of the tape machine. When I disconnect the molex while leaving the xlr output going into the Fireface, I still get the sound when the tape machine is playing.

 

[Biasrocks]

Interesting. You're saying that without the output being connected to any electronics inside the deck you're still getting the sound. If that's the case it sounds like it's mechanically or Emi induced. Have you tried physically moving the power supplies away from the machine or re-orient them.

Are the motors stock? Have you tightened them down, verified ground connections?

Btw, I/O on these machines are provided on Tuchel connectors. i have never seen XLR I/O's on a JH. Most likely an after market mod, perhaps this is the source of your problem.

Regards,
Mark

 

[Scrappersa]

You're saying that without the output being connected to any electronics inside the deck you're still getting the sound. If that's the case it sounds like it's mechanically or Emi induced.

Yeah, that's exactly it.

The motors are stock. I have not tightened them down but I will when I get home from work. I'll also check the ground connection.

I didn't realize that the input and output were done with tuchel connectors.

 

[Biasrocks]

I didn't realize that the input and output were done with tuchel connectors.

Upon further investigation, JH-16's are XLR; JH-24's are all tuchels.

Regards,
Mark