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R/E/P => R/E/P Archives => Bruno Putzeys (Designer) - Dave Hecht (Master Tech) => Topic started by: cdnaudio on December 30, 2007, 01:53:28 AM

Title: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 01:53:28 AM

Hi All,

New to the forum.

I have an OTARI MTR 90 MKII that is recording intermittent loud static clicks... all about the same amplitude, on all tracks. Bias, erase, demag have all been done - repeatedly! Reseated Molex connectors. Checked bias and erase frequencies on an Oscilloscope, they look very clean. Machine sounds great otherwise. The clicks only start after the machine has been on awhile on a given day.

Being a newbie to tech-ing and scope operation... I'm not sure if what I'm looking at is correct. The 5V and 24V rails seem clean (looking at the DC output in AC scope mode, super zoomed in - there's a tiny bit of ripple), but both sets of +/- 20V buses look like jittery sawtooth waves. None of the rails measure out exactly right, but they're all pretty close.

Does this sound like I need to re-cap to anyone here?

I'm not seeing any sort of intermittent pop on the scope, but as I said, I'm not sure what I'm looking for exactly. Any suggestions would be much appreciated!

PS: If I do need to recap... how the heck do you get the PSU out with all those connectors on the side????

Thanks!
Bob

Title: Re: MTR90 MKII L - Recording Clicks
Post by: thedoc on December 30, 2007, 02:02:13 AM

What condition are the heads in?

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 02:22:31 AM

They've had their last lap, but don't look particularly worn. They do record clean for 20 minutes after initial power up...

Obviously I'm hoping heads aren't the issue.

Title: Re: MTR90 MKII L - Recording Clicks
Post by: sodderboy on December 30, 2007, 12:34:49 PM

It is like single clicks, or clustered clicks?

Since it is all tracks after a warm-up, I would be looking at any global voltages with the scope- all PSU voltages, erase and bias signals, mute logic, etc.

Look at the motherboard schematic and you will see how many common signal connections that should be checked.

Try a re-seat of the head connectors- machine off of course!  You can check for continuity between the head shields and the machine deck.

If still no joy, remove the remote.

And as for the PSU caps, you have to break the whole thing open like a nut.  Re-crimp all crimp connections, replace any hard wires, and CLEAN all lugs, screws and cap studs with alcohol.  The lug connections are a weak link in any power supply.
Mike
PS: and make sure that the clicks are not coming from the console!

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 01:06:04 PM

Thanks for your help... it's definitely not coming from the console. Machine is disconnected for now.

When I check the voltage rails, what sort of things am I looking for on the scope?

Title: Re: MTR90 MKII L - Recording Clicks
Post by: Rick Sutton on December 30, 2007, 03:39:04 PM

OK this is a long shot. Any possibility that this is static discharge? I have seen this on old decks with worn tape path/heads. Has this come on recently with cold dry weather?
Just a thought. If this is a possibility try raising the humidity in the room and see what happens, this sometimes helps, Also see if different tape formulations affect it.

Title: Re: MTR90 MKII L - Recording Clicks
Post by: Dave Hecht on December 30, 2007, 03:58:59 PM

Sounds like you may have a couple of issues here. As for the static noise, the first thing I would check for that is the heads. When I've run into that in the past, it's usually bad grounding on the heads. Try measuring between the head ground and the chassis, as Mike suggested. You should not just have continuity, buy very low resistance (no more than a couple of ohms). Ive seen machines where some tracks had higher resistance, and the static only occurred on those tracks. As Rick pointed out, humidity will affect static as well. Very dry conditions can cause static problems.

As for the +/- 20 volt rails, I'd double check your measurements again. The waveform you described definitely does not sound right.

Dave Hecht

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 04:18:20 PM

Thanks guys...

.2 ohms between heads and chassis (same as between 2 points on the chassis), I think we're good there?

I'll try upping the humidity and look at those rails again... the problem seems unaffected by tape stock. Nothing looks too worn in the tape path, it all looks pretty new actually.

Bob

Title: Re: MTR90 MKII L - Recording Clicks
Post by: Dave Hecht on December 30, 2007, 04:55:31 PM

Where are you taking the measurement on the heads? I can't remember on the Otari, but on a Studer, you can measure ground for each individual track at the outside of each track. Are you measuring the headblock or the individual tracks? If you're getting .2 ohms on the tracks, you're fine.

Another thing to check for. How is the machine grounded? Is the power cable ground lifted? If so, try re-connecting the ground.

Dave Hecht

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 06:04:46 PM

Hey Dave,

The machine is on an iso ground, orange 20 amp outlet, with a 10 gauge home run ground to the box (only about 12 feet away). It's quiet as a mouse...

The high gauge ground wire wouldn't be inviting any crap in would it????

Just measured the head block, but I'll try the tracks too...

Thanks,
Bob

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 08:02:24 PM

Just spoke to another tech friend who suggested it was possibly an op amp, diode or cap in the PSU - and that my scope possibly isn't fast enough to catch the spikes.

I've figured out that the sawtooth wave I'd seen on the +/- 20 rails was actually my Neutral connection being a little loose. When connected correctly, it's just showing a few little harmonics, but nothing awful.

It was also suggested to leave the machine on for a couple days and see if it stabilizes. It's been off for a couple years, and only on for a couple hours here and there for testing...

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 30, 2007, 11:31:54 PM

Hey, I think I figured it out... it was the outlet...

I shut it off at the box and plugged the machine into a regular "dirty" outlet.. clicks are gone. Now when the machine is OUT of its closet, and plugged into the clean outlet, it's fine... but when I put it back in, it clicks.

I'm wondering if the wire run, where I put the outlet, is the problem. I located it at the front left bottom of the machine for easy unplugging when storms happen. The problem still occurs when the machine is plugged into a different outlet, but the "clean" circuit is still live.

I suspect if I relocate that outlet it will fix it?

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on December 31, 2007, 11:48:23 AM

Naw... that's not it... sounded too stupid to be true as well. It was a coincidence...

So here's what I think I've figured out so far: The tape machine is fine, though cleaning and reseating all the molex connectors made it a bit quieter.

The issue is either power, or something to do with a console connection (though I thought I'd eliminated that possibility 2 weeks ago), OR the machine just needed to sit "On" for a couple days...

When  I look up these threads for help, I find it very helpful when the poster wraps the thread up with, "fixed it! here's what worked for me..." so if I have any additional information I'll pass it on. It's amazing how little info is out there on MTR90 problems...

Title: Re: MTR90 MKII L - Recording Clicks
Post by: sodderboy on December 31, 2007, 10:39:33 PM

Let cold rationality rule.  Keep track of what you do at each step, and look to the previous step to make sure that a "swap" was put back before you go farther.
If a PSU or logic voltage is intermittent, you will see your horizontal scope line drop or spike on the scope, even a slow scope.
I wanted to mention the grounding of the heads themselves, but I did not want to run into a althemusicwizard moment with this poor fella taking DMM probes to the edge of the individual heads.  I use sharpened killer probes for that work so that I avoid a costly slip across the stack.

It IS happening globally, isn't it?

Time to take a fresh-baked ham over to our neighbor's house for a little shin-dig.
Happy New Year!!!
Mike

Title: Re: MTR90 MKII L - Recording Clicks
Post by: Larrchild on January 01, 2008, 12:27:39 AM

Are the same noises going on all tracks at once when all are armed or do the individual channels do it randomly. but only on that channel?

Title: Re: MTR90 MKII L - Recording Clicks
Post by: Dave Hecht on January 01, 2008, 04:26:16 AM

Spoke with a friend of mine who used to be the Otari Tech here in LA. Cleaning the molex connectors was one of the things he mentioned. He also suggested checking for burn marks or melting around the molex connectors. Apparently, there were some issues with questionable crimps becoming resistive and heating up. Also, what lot number / serial number is your machine? He also mentioned some factory update relating to this type of issue on some lots.

Dave Hecht

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on January 28, 2008, 12:08:15 AM

Thanks for your help everyone... cleaning the molex connectors with Deoxit 5 made the clicks go away, and I'd swear the machine is running quieter. Couldn't be working better.

Thanks again.

Title: Re: MTR90 MKII L - Recording Clicks
Post by: amorris on January 28, 2008, 03:55:01 PM

Nice.. Dave, any explanations as to what is happening?

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on June 14, 2008, 11:25:24 PM

Opening this thread up again, thanks everyone for your help last time.

My "random static recording on all tracks" problem has recurred after 6 months... I've tried cleaning and lubing the molex connectors but it hasn't worked this time. Haven't cleaned the head connections yet.

The machine has been powered up most of the 6 months it's been in use and has been running great until today.

Any other ideas besides the ones that have come up so far?

I'm going to make sure I've cleaned all the appropriate power connections in the mean time.

Thanks in advance!

Title: Re: MTR90 MKII L - Recording Clicks
Post by: amorris on June 17, 2008, 10:24:24 AM

you need to probe around while this is happening. youll see it. then work upstream to find the source.

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on June 17, 2008, 11:10:45 AM

Fixed again.

I've been mixing more than recording lately and I could be wrong here, but it seems like the machine is happiest when it's working.

I cleaned all the molex connectors and the D subs that connect the heads... didn't immediately fix it.

Then I erased 4 reels of tape. Clicks were gone.

So we're good for now. If anyone has any input to add it is more than welcome.

Thanks!
Bob

Title: Re: MTR90 MKII L - Recording Clicks
Post by: compasspnt on June 20, 2008, 10:36:33 PM

What has happened with this MTR-90 issue over the last six months?

Title: Re: MTR90 MKII L - Recording Clicks
Post by: cdnaudio on June 30, 2008, 07:21:12 AM

Cleaning the molex connectors and letting it run for a while fixed the problem both times it came up within the 6 months.

When the machine is running, it's running perfectly. Sounds great.

I suspect the problem recurred as I hadn't been recording for a month or so, mostly mixing. Though I did clean the connectors again, the problem didn't actually go away until I erased a few reels... so best I can figure it's happier when it's working.

I suppose this could mean a capacitor problem on the horizon, I'm not sure... but the machine is working fine now.

Thanks for asking.

Bob