MCI JH110

[CurtZHP]

O.K. I spoke too soon.

While doing some other adjustments on the machine, I'm hearing a noticable hiss in the right channel when recording a 10kHz tone and listening to the output of the playback head (REPRO).

Otherwise, she's fine. Any thoughts?

2 track?

Yes.





(edited because I think I found the problem)

[Brad McGowan]

After a few weeks off we're visiting this monster in the living room again. We shotgunned all of the ICs and sockets and the transport seems to be rock solid in all speeds. Now we're having trouble trying to get our tape recorder to record.

Audio passes through when the channel is on Input. Nothing comes back when on Repro or Cue. Is there something obvious I'm missing that would prevent the signal from either getting to or returning from the heads? The head connectors on the rear of the electronics are connected.

Also: This machine came from a tv station and we're told that it was a JH-110A that was upgraded. We're running into a few inconsistent things (like I didn't think there were supposed to be these red sockets on an JH-110A but they're all over ours) that are making troubleshooting a little less streamlined than we thought. There is the white cylinderical transformer on the Repro cards which matches our 110A manual but the card also has two 2003M labeled can ICs on the board where the manual shows the 2001. The thought from an earlier post on this thread that the 110A used the 2001 and the 110B used the 2003/5534 (which are in ours on the Bias and Audio Motherboards). Were there a standard set of upgrades to the JH-110A that were frequently done or was it just as much as whatever someone felt like doing?

I just picked up a JH-110A 8-track and am having a similar problem with getting one channel to record. It shows level on input, but nothing comes back when the machine is in repro and the VU meter doesn't move. Did you ever solve this problem? I'd love to know what it was!

Regarding the 2003M can IC's.... I think I can shed some light there. MCI made an 18V version of the "A" right before the "B" version came out. Unlike earlier "A" versions it didn't have the transformer input but had an electronically balanced input using a 5534 (2003P). Like you I have the 24V "A" manual and it doesn't mention any of this stuff.

Does anyone know a good source for the switch caps with the colored indicators? I know that C&K makes them for F-series pushbutton switches, but I can't seem to find a supplier.

thanks,
Brad

[Beneficial]

I had a similar problem with my JH110C. REC mode seemed to work for a channel but then I had nothing playing back in REP mode. In my case the molex connector that connected the tape head wires to the back of the audio electronics drawer was dirty/loose. I Cleaned that and reconnected it so it fit tight and everything worked fine.

[Brad McGowan]

What's the easiest way to get access to the back of the audio electronics drawer?

thanks,
Brad

[Beneficial]

Hmm... I have a 2-track deck so the electronics sit under the transport. In the 8 channel model I'm not sure how it's wired up.

[airloom]

In response to dirtdog's post:
No, we haven't fixed the damn thing yet.
- John

[Brad McGowan]

I return seeking the wisdom of the experts here. I?m still having a couple of problems that I can?t seem to sort out:

1. The locator counter seems to only function properly half the time. Some times when tape is rolling it will just stop counting. It seems to randomly work. It makes trying to locate a total pain. Sometimes if I turn the machine on/off it comes back to life. Other times it remains ?stuck?. What might cause this? What?s the best way to troubleshoot this issue?

2. Channel 2 doesn?t seem to completely erase what was previously recorded as new material is being recorded onto the track. The previous signal can be audibly heard underneath the new signal as I?m monitoring in repro. The odd thing is that I was having this problem on channel 1, but it migrated to channel 2 when I moved channel 1?s record card to channel 2. What on the record card might cause this? The AC voltage levels on the large variable capacitor (whichever one relates to erasure) on the motherboard seems to be in family with the rest of the deck. Any ideas?

Thanks in advance, smart people!

Brad

[CurtZHP]

Brad,

The voltage on that capacitor should be at least 40V. What were you seeing?

It could also be a bias adjust issue.

[Brad McGowan]

Yeah, I see about 46VAC.

Tell me more about the bias adjust issue.

Brad

[CurtZHP]

Actually, the more I think about it, I'm not sure if adjusting the bias cards will have any effect. Although, it is possible that the bias oscillator (which is common to both channels and the erase head) could affect it.

What do you have in the way of documentation on your machine? Do you have a the tech manual?

[Brad McGowan]

I have the full original manual with all the schematics.

Brad

[CurtZHP]

There's a page in there about checking the bias oscillator. I was thinking of that, but I'm having a hard time convincing myself that's the problem.

/still thinking.....

[ladewd]

Brad,

Erase head wrap has a lot to do with erasure levels between channels. Think about it, the erase heads are not in line with each other. the trick is to get the wrap so that each channel has equal amounts of erasure. After that, there's the ringing up of the erase coils and caps, but this is the easiest adjustment to start with. As you move the head from side to side, you will see channel one erase better, then channel two. Get it in the middle before you go into tweaking coils and variable caps. At least that's my .02.

Don't know what to tell you about the locator. Could you have an intermittent connection on the count generator photocell? I'm not sure I'd go diving into the processor board untill I've determined that you're getting a good tach from the counter.

Edit:

OK, I didn't notice you swapped cards and the problem followed the card. Still, give the wrap a shot. When you swapped record boards (not bias boards) the erasure got better???

CA

[Brad McGowan]

Okay the locator seems to work now that I jiggled the connections and sprayed some contact cleaner. The erase head wrap should be about perfect since I had the heads relapped and optically aligned by JRF Magnetics.

My damn MCI JH110 is still driving me crazy though. Can someone please measure the RMS AC voltage on the left tab of the erase peak trimmer C1 on the audio motherboard while recording and tell me what you get? I think it's "point C" on the motherboard schematic in the manual. The manual says that I should be able to get 60-70 V RMS with trimmer R9 on the strip board set fully clockwise. I'm getting more like 40V, and I still hear the old tracks on the tape when recording over them.

I finally obtained a frequency counter so I have the bias frequency dialed in finally. I just need to sort out the erase voltage levels. Will the erasure be deeper with the bias frequency at 120kHz rather than some other frequency? I got really frustrated and left the studio, but I probably should have seen how well the erase was working once I had the frequency properly adjusted.

thanks,
Brad

[mattallen]

The master oscillator has to be 120khz