Ampex MM-1000 Story...

  • Thread starter Thread starter sweetbeats
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sweetbeats said:
I'm going to run the ground wire to the 24VDC supply is shown in the schematics, and star-ground from the breaker panel lug to the transport plate, the console chassis, and maybe even the overbridge.

What do you think fellas?
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I say if it works, go for it. I'd just hate for this issue to be a regression of some deeper issue going forward which blows up in your face mid-session. Could just be one-of-those-things, quirks that don't go away and aren't necessarily harmful.
 
That's EXACTLY why I'm looking for some affirmation here from anybody smart which is pretty much all y'all.

I have no interest in additional grounding being a band-aid fix.

So, anybody?

I might shoot a video going over this as it might be easier to digest...

But I'm hopeful that grounding is really the issue since the ground wiring presently on the machine doesn't match what the schematics spell out...
 
sweetbeats said:
This is a side-note here...chassis grounding...look at that system schematic on 8-5/6 again, and particularly in the upper left of the schematic at TB1, J1 and the Power In connector. Again, J1 is the input of the 24VDC regulated supply. TB1 is that screw-terminal block mounted to the breaker panel. Notice that the ground from the Power In connector goes to the chassis, to TB1 and branches to J1. Guess what? On my MM-1000 the ground comes from the Power In connector straight to TB1, and then from TB1 to a stud on the metal breaker panel, and then...that's it. :eek: This is not good right? The breaker panel is just a 2U rackmount panel so even if IT is connected to ground, there is no gaurantee that it will conduct ground to the rest of the chassis. It is painted metal, and a fairly heavy coat at that, and that's supposed to ground the rest of the chassis?? And, you got it right, there is no ground to the 24VDC supply. I pulled J1 apart and there is just hot and neutral lines in there even though there is a lug for a ground. So I'm thinking regardless of anything else I need to run a ground line from TB1 to the 24VDC input J1, and also star-ground the rest of the chassis including the transport plate??
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Is that what you're referring to? The discrepancy of the grounding between what you have and the schematic?

You asked if the breaker panel chassis is supposed to provide grounding to the whole chassis or not. I'd like to know: If you set your multimeter for a continuity test, (you know, the one where it beeps if there's zero resistance) put one probe on the breaker panel plate and one probe on the transport. Is there beepage?

Are you 100% certain that you're not missing any components to the chassis? Any extra trim panels and whatnot?

If you reconnect the transport plate to the control relay box, do you still get voltage if the "mains" throw switch is 'off'?

Now on the schematics page 8-5/6, the only other mention I See of GRound is J11 and P701. Check that out for oddities.

Correct me if I'm wrong:
TB1 is a screw-down terminal strip. Not a connector, right? There's not an opposite side to TB1 where wires can travel to other things? If that's true, then when Mains is off, there should be only neutral and (ground? or not in your case?) going to J1. How could those two connections still leak out 6 volts to the transport plate?

Is it possible to remove components of the actual transport and test? I know you've tried disconnecting supply cables to each transport component from J2, but what about actually taking out those respective components altogether and testing? If this is being caused by wonky continuity from one particular component on the transport, this would tell you.
 
I almost forgot!

With the Mains throw OFF, and J2 unplugged from the transport plate, (but still hooked up to the Control Relay box), what voltages do you have coming out of those bare pins on J2 coming out of the control relay box?

Obviously, if voltage is getting to the transport plate with mains throw off, it's gotta be coming through that cable somehow. Which pins are hot?
 
Muck, et al, here is a video that will hopefully make things more clear (I hope):

YouTube
 
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I keep Ohm's law playing back in my mind --

A high amount of voltage on the transport plate, along with a very low amount of current, is only possible with an extremely high resistance.

Given that you didn't have any continuity between your ground and transport plate, then this is obviously the equivalent of an extremely high amount of resistance. Even extremely low currents will be represented by extremely high voltages, due to the high resistance.

Summary of my ramblings: It makes perfect sense to ground the transport plate as you have done. If it fixes the issue, and all other things work they way they should, go for it. A chassis ground doesn't do much good if it doesn't ground the whole chassis, does it?
 
Interesting problem. I was wondering if the grounding post on the panel should be painted. I'm sure it would make little or no difference in this situation, but I was just courious. What I can't understand is why you have power where none should be. I hope you figure it out.
 
I was wondering if the grounding post on the panel should be painted. I'm sure it would make little or no difference in this situation...
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Ed, what do you mean exactly? Are you saying it looks like the post IS painted and shouldn't be or if it is NOT and should be...

I think the problem is figured out...just looking for some validation from brainy folks...

The trick is that there basically ISN'T voltage where it should be...yes there is measurable "voltage" on the meter, but the current is so low, and I believe the cause to be the fact that, because the chassis and transport plate is not grounded the neutral leg is able to "float" away from the ground reference.

The neutral and ground legs are tied together in your service panel. The ground is there as a safety, okay? If something goes wrong with your neutral leg the voltage present on the hot leg is going to want to resolve itself and it'll do it through you if there is no other way. That's what the ground is for.

I can't explain the physics of it, but I think I understand that once the ground and neutral legs enter the system they should go the same places so they stay at the same reference. At present my ground stops at the MM-1000 breaker panel, and the neutral continues on, the differential between the ground line left behind at panel and the neutral reference elsewhere in the machine drifts apart the futher it goes...why there is anything at all to reference on the transport plate when neither the neutral or hot legs connect to the plate (because I have tested continuity between the plate and the neutral and hot legs and there is NO connection) I have no idea...

So, I *think* there really isn't a problem per se except that the proper grounding was never put into place.
 
sweetbeats said:
So, I *think* there really isn't a problem per se except that the proper grounding was never put into place.
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I was suspecting that myself but didn't feel qualified to jump in.

I suspect that your machine came from the era of "what doesn't kill you, makes you stronger". :laughings:

I mean, I wish I had a dollar for every time I used to get electrocuted in my buddy's basement, when I touched my lip to the microphone that was running to an old Traynor tube guitar amp. The ground loops were horrific! :D

And, we survived them! :)

Cheers! :)
 
sweetbeats said:
Ed, what do you mean exactly? Are you saying it looks like the post IS painted and shouldn't be or if it is NOT and should be...

I think the problem is figured out...just looking for some validation from brainy folks...

The trick is that there basically ISN'T voltage where it should be...yes there is measurable "voltage" on the meter, but the current is so low, and I believe the cause to be the fact that, because the chassis and transport plate is not grounded the neutral leg is able to "float" away from the ground reference.

The neutral and ground legs are tied together in your service panel. The ground is there as a safety, okay? If something goes wrong with your neutral leg the voltage present on the hot leg is going to want to resolve itself and it'll do it through you if there is no other way. That's what the ground is for.

I can't explain the physics of it, but I think I understand that once the ground and neutral legs enter the system they should go the same places so they stay at the same reference. At present my ground stops at the MM-1000 breaker panel, and the neutral continues on, the differential between the ground line left behind at panel and the neutral reference elsewhere in the machine drifts apart the futher it goes...why there is anything at all to reference on the transport plate when neither the neutral or hot legs connect to the plate (because I have tested continuity between the plate and the neutral and hot legs and there is NO connection) I have no idea...

So, I *think* there really isn't a problem per se except that the proper grounding was never put into place.
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Sorry I wasn't more clear. I meant it looked painted and I didn't think it would make a good ground with paint on it. I hope you have it figured out.
 
It is good to hear that you got nothing out of the bulb. As you may recall we (I) was worried about your comment indication that you could feel current passing into your fingers. Let's hope that that was not the case rather than an intermittent fault with some power behind it.

I think that tying the transport plate to the protective ground is a good idea (provided Ampex is not up to tricks as I expect they were not).

A high impedance meter loads the DUT less than a low impedance meter. Thus it tends to be more accurate. But it also picks up very low power level voltages that can be induced into metal plates that are not grounded. Picks up in the sense that the plate acts as an antenna..

--Ethan


sweetbeats said:
Okay...to make a long story short (no pun intended), I couldn't oven get anything out of a 25W bulb...so for all intents and purposes there is no current there. This is supported by the fact that I measure no *voltage* when I set my cheap-cheap-cheap DMM to VAC and probe between the transport plate and househld ground...its a cheap meter and the impedance is too high I bet, but the voltage is measurable with my Fluke 85.

So I temporarily ran a ground wire from the ground buss on the breaker panel to the transport plate and guess what? The voltage drops to 0.2mV *with everything hooked up and running*!!

SO...no real current to speak of and voltage drops to basically nothing when I tie the ground to transport plate.

Safe to assume this is just a matter of a floating neutral line and the proper solution is proper grounding?

I'm going to run the ground wire to the 24VDC supply is shown in the schematics, and star-ground from the breaker panel lug to the transport plate, the console chassis, and maybe even the overbridge.

What do you think fellas?
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Ethan...thank you. That's reassuring.

I wondered about the plate just picking stuff up...that's a lot of metal and there's a radio station down the street so...

I did a more quantitative test today...I set my meter to AC current and measured between the transport plate and the mains ground and it was 118mA...that's okay right?

Is it safe to assume that with absolutely no continuity between the hot or neutral outputs from the breaker panel and the transport plate that there isn't a short, and the current is the result of some sort of floating reference?

Ethan, I'm pretty much certain that I did feel current, but not anything ike tingling...it felt like...like...118mA. :D

Ed, yes the threaded stud is painted, but forget that concern...so's the breaker panel...console...that ground lug wouldn't propogate to anything else anyway...I took my continuity tester around the rest of the system today and even with stuff bolted up nothing is connected to the ground.

I believe this is a frankenpex...so I can't just assume things are the same as the schematic. And the grounding is just...totally absent...for now.

I just wish I could know for sure that it is just a result of it not being grounded properly, and not some wierd killer thing...

The voltage at the plate drops in half each time I disconnnect something from the transport.

*sigh*

Maybe I could just toss it in the car and bring it by your place, Ethan. :laughings::laughings::laughings:
 
Its only 118 mA.....

"Death can occur from any shock that carries enough current. Small currents (40 mA - 700 mA) usually trigger fibrillation in the heart which is reversible via defibrillator"

So do you have a defibrillator and someone there to apply it to you?

I'm not sure what you mean by mains ground. Is this the:

A) protective ground at the outlet that the Ampex is plugged into.
B) the neutral wire at the outlet that the Ampex is plugged into.
c) something else.

All sheet metal and "plates" should be connected to the protective ground (the green wire) directly or through each other.

The neutral wire (white) is not a ground. It is the return wire for the (black) hot wire. Any resistance inthe neutral wire forms a voltage drop that can become excessive and hurt you if you treat it as a ground.

-Ethan
 
Ethan, by "mains ground" I'm talking about the ground terminal at the outlet to which the Ampex is plugged into.

DANGIT!!!

106VAC 118mA...the MM-1000 is a DEATH MACHINE!!!

I'm so tweakered over this...thought I had it figured out bu I'm clearly back at square 1...even further behind now since I now understand that its not just some drifting reference differential.

But WHY wouldn't it light that 120V 25W bulb??
 
watts = volts x amps right?

106V, 118mA...so 106V x 0.118A = 12.51VA or watts...12.5 watts of power ought to make that 25W bulb glow nice right???

ARG!
 
I was told once upon a time that DC current is far more dangerous then AC current. 118 milliamp is just a shade over 1 watt of power with the 105 VAC pushing it, which would explain why it won't power your 25 watt bulb.

I'm tempted to suggest that you're chasing a non-issue.

Cheers! :)
 
Jeff, I so want to believe that's true, but according to my understanding, a milliamp is 1/1000 of an amp, so 118mA is the same as 0.118A. That multiplied by the 106VAC present at the plate when everything is hooked up is about 12.5 watts.

Am I wrong?

So that's why I'm thrown back to confusion on this and thinking I need to pull everything apart again...but...there's no continuity between the hot and neutral legs and the plate...:???:...oh me, oh me.
 
Well now, 118 mA is not RFI pickup. It represents real power in the form of leakage current. You need to find where the leakage is coming from. Some insulation or blocking cap or something is sourcing that current. Or perhaps is is coupled capacitivly to some other charged plate. 118 mA is 7.4^17 electrons per second in case you were wondering :)

In terms of the actual power I wold suspect that the light did not lite because the voltage dropped from the 100+ volts no load to something much lower. thus a much lower wattage.

Perhaps disconnecting everything near it one by one without frying yourself or your machine will help find the source. Then be sure that things are well grounded to the protective ground.

Do I recall correctly that you measured little or no voltage between the protective ground and the neutral wire at the outlet you are using?

--Ethan

PS Sure, just put that beast into a moving truck and bring it up.
 
sweetbeats said:
Jeff, I so want to believe that's true, but according to my understanding, a milliamp is 1/1000 of an amp, so 118mA is the same as 0.118A. That multiplied by the 106VAC present at the plate when everything is hooked up is about 12.5 watts.

Am I wrong?

So that's why I'm thrown back to confusion on this and thinking I need to pull everything apart again...but...there's no continuity between the hot and neutral legs and the plate...:???:...oh me, oh me.
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You're correct. My math was off. :o

scuttles out of thread...

Cheers! :)
 
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