Outline · [ Standard ] · Linear+ What To Use For 'scratchy' Pots?, want to clean the pots on an MX-80

[sweet_beats]

Okay.

What do I use and how do I go about helping the gain/pan/level pots on my Tascam MX-80 rackmount 8 X 2 mixer to be less scratchy?

I picked this thing up on eBay for $35+S&H (!!! !!! I don't think they knew what they had...not that this is a sought after unit or reknowned for its pres, but I think I got the better end of the deal...) and it is in pretty good shape cosmetically (7-8 out of 10), has all the original send-receive jumpers, knobs, etc. The only issues with it are channel 7 only works up to the send patch point, and the controls are scratchy throughout. Regarding input 7, if you try to route the input to the L-R buss it is dead (i.e. jumper in place, preamp provides no gain...turning the gain knob all the way up and thumping the mic doesn't activate the clip LED as it does when the jumper is removed...). I hear some humming. I think it is a short. Its not a big deal because I plan on only using it as an 8-channel preamp anyway and bypassing the mixer via the channel send points, but I'll probably tinker anyway and see if I can trace where the issue is. The pan and level controls are on a stacked pot and the level pots on channels 7 and 8 look a little bent, so maybe they got struck at some point that's the issue with channel 7...anyway, most of the controls are scratchy when rotated causing some inconsistent performance particularly at the gain-amp stage. How do I clean them up?

BTW, for reference, I think this unit features the same pots as are found on the likes of the 234, 34B, and M-200 series consoles of the same era (I'm assuming as the knobs are the same and I'd assume they would be using the same internal hardware as well).

Anybody know if this uses the same pre's as the M-200 series consoles (i.e. M-208, M-216), and any comments on them? This is my first exposure and my first impression based on my preliminary function tests last night (spoken vocal ---> SM-57 --> MX-80 --> Alesis Monitor I mkII Actives) was favorable. Very accurate "broadcast" character with healthy low-end presence. I was suprised actually, and I'd probably get lambasted for complaining at $5-6 a pre!!

[MidiMagic]

I have found nothing better than Caig CaiLube MCL moving contact cleaner.

The hard part is getting it into the parts that need it. You have to open the unit, and some units have sealed pots.

I would suspect the contacts in the send jack. They are supposed to close if there is no plug in the jack. If they are not closing, no signal gets past the send.

This is a fairly common problem, especially if someone hit the plug while it was in the jack, or if the contacts get dirty. Use the same Caig product to clean the contacts.

Open circuits hum. Shorts to ground make no sound at all, unless they are intermittent (when they grickle).

Another possibility is an open connection on an XLR jack in the mixer. It will still pass signal, but at a low level with a lot of hum

This post has been edited by MidiMagic: Jul 11 2007, 02:09 PM

[sweet_beats]

Thank you for the input.

I have found nothing better than Caig CaiLube MCL moving contact cleaner.

I've heard of it. I'll check that out.

The hard part is getting it into the parts that need it. You have to open the unit, and some units have sealed pots.

The unit is open. I can access the face of the pots. How do I tell if they are sealed, and what do I do if they are?

I would suspect the contacts in the send jack. They are supposed to close if there is no plug in the jack. If they are not closing, no signal gets past the send.

Is this true for RCA jacks? The send and receive jacks on the MX-80 are unbalanced RCA jacks. Signal IS getting past the send jack though. If I pull the channel 7 jumper, connect a mic into input 7 xlr and then patch the send jack to my monitor setup with nothing in the receive jack everything is great. If I then put the jumper back and route the monitor source cable to one of the buss outs (balanced or unbalanced), there is nothing, whereas this works with all other channels.

Open circuits hum. Shorts to ground make no sound at all, unless they are intermittent (when they grickle).

Right...okay. That makes sense. Actually, the hum occurred while I was experimenting plugging the mic into another input and patching that channel's send jack to channel 7's receive jack...it was late...I didn't really think it through at the time and as I review my actions now that doesn't make sense to try that.

No, to clarify, when a mic is plugged into input 7, and the jumper is in place, I can crank the gain, channel level and master output level knobs and it is eerily quiet, including nothing making it from the mic to the speaker so I guess it isn't humming now that I think about it (except when I'm trying a poorly thought out cockamamie experiment... )

Another possibility is an open connection on an XLR jack in the mixer. It will still pass signal, but at a low level with a lot of hum

You mean like if the internal wiring for pin 2 OR pin 3 of channel 7 was compromised? But that wouldn't explain why it performs great when I patch only to the send jack with nothing in the receive jack. If I'm understanding you correctly, that would be a pre-gain stage issue but I'm suggesting that the circuitry is healthy all the way up to the send jack.

I'm attaching pictures of the front and rear of the MX-80. Not great pictures but all I could nab from where I'm at.

Attached thumbnail(s)

[pianodano]

SB,

the pots are normally self cleaning wipers.

Old engineers trick for scratchy pots:
Wrap a shoestring around pot and spin it up for a couple of sconds. Wala - all done.

Danny

This post has been edited by pianodano: Jul 11 2007, 07:24 PM

[sweet_beats]

midimagic, thanks again for the tip.

For all following this thread, Caig CaiLube MCL is now the DeOxit Faderlube according to the Caig Website.

Looks like the right stuff.

dano, thanks for the shoestring tip. I'll try that. Instinctually I always take and sweep a scratchy pot back and forth several times and that seems to help. Shoestring would make that more effective. Thanks!

[sweet_beats]

UGH!

The problem is not simple...everything is A-OK with the cross connects from the I/O jacks (i.e. XLR input, RCA send and receive jacks) to the control board, so it is a component on the control board or a fault on the control board itself. Having no schematic for the MX-80 makes it a challenge, and it doesn't help that I barely know more than what it takes to cause trouble.

I'm suspecting a problem with a pot as one of the shafts seems like it may be *slightly* bent, and the knob had a small abrasion on it so that is where I'm going next.

This is just an update I guess, but I'm open to any suggestions.

Attached thumbnail(s)

[zenbubblegum]

Hello there,

I recently got a TEAC 144 (£20, so beautiful, easily the best item I've ever bought on eBay) but it too has scratchy pots like sweet_beats' mixer. Will this FaderLube stuff be the ticket for me, too?

Where should I be squirting it? Do I need to open the thing up, get the casing off and spray around all knobs, faders and contacts? Is there any ill-effect in being over-zealous in the spraying?

Also (slightly off-topic, I hope the mods won't mind), if anyone wanted to suggest some general care and maintenance tips for an aged but feisty Portastudio, it would be much appreciated.

Or just point me in the direction of a few threads - I've already read a bunch using "TEAC 144" as the search term, but there may be more useful info lurking under different headings.

I'm no electrical engineer (far, far from it) but I'm not afraid to take the back off something and at least have a look inside, maybe do a little housekeeping. Sadly, I don't have a manual, so any schematic references would be lost on me.

Thanks in advance.

Jonathan

[MidiMagic]

One little squirt is enough. Don't overdo it. I did once, and warped a switch stack. It also eats certain plastics.

There is usually a little slot in the side of the can on the back of a pot where the terminals come out. Put the lube in there, then rotate the pot end to end many times.

On linear faders, you can put it down the slot on the control panel the handle comes out of.

If the pot is sealed, the shaft is the only entrance point, and that is iffy. But I usua;lly don't have trouble with sealed pots.

I just helped someone restore a 1960s Fender Stratocaster with this.

My dealer still has many cans of the product under the old name.

[MidiMagic]

Hello there,

Or just point me in the direction of a few threads - I've already read a bunch using "TEAC 144" as the search term, but there may be more useful info lurking under different headings.

I'm no electrical engineer (far, far from it) but I'm not afraid to take the back off something and at least have a look inside, maybe do a little housekeeping. Sadly, I don't have a manual, so any schematic references would be lost on me.

Thanks in advance.

Jonathan

Get a related product, CaiKleen RBR, and clean the belts and pinch roller with it.

[zenbubblegum]

Thanks, MidiMagic. I've already read a number of your previous posts across these forums, so I appreciate your help on several issues.

I've ordered a can of FaderLube, so I'll get busy when that arrives. I made a call to the repair shop that are currently servicing my MSR-16S (it's been four months so far...) and was quoted £150 to service this 144.

He was very positive about it, as apparently a lot of parts are still available, but the machine only cost me £20, so I think I'll do what little I can myself! It works and records beautifully, it's just the tape transport is somewhat noisy. I'll just use hypercardioid mics!