PS/2 30-286 potential PSU issue

[kishy]

Alright, so I had THOUGHT that these PS/2s had a power supply that, when switched OFF, actually was off...apparently not.

I just heard a buzzing noise in the room, and I eventually narrowed it down to the 8530. I don't normally leave my machines plugged in when not in use, as you may recall from a recent thread about leaving XTs turned on for extended periods of time, but in this case I was planning to go back and use it later (very soon actually, it's getting lateish). Yanking the cord caused the buzzing to stop immediately, with no delay or slow fading. Pull plug, silent.

As an aside, it looks like I was justified in keeping ALL machines unplugged, regardless of PSU type. Take that, doubters.

The switch was off...I thought on these the switch (to be specific, the big plastic red one inside) was connected directly to AC power so if it is turned off, there is no electricity being supplied to any part of the system?

If that's not the case why was there buzzing? What electronics come "before" the big red switch?

Machine is unplugged and not being used again until I figure this out. Would prefer not to risk damage to the rest of the (otherwise flawless) machine.

 

[NeXT]

Hmm. As far as I know there isn't anything before the red switch.

 

[kishy]

Hmm. As far as I know there isn't anything before the red switch.

Yeah...that's what I had always thought. I guess I'll have to take it apart (the PSU) and check both poles of the switch for continuity when off. I'm not an electronics expert but I suspect if one pole is not being properly turned off and there could be a possible "leak" to ground, some things might make some noise...or something to that effect. First thing to check is definitely that the switch does work of course.

 

[Chuck(G)]

Is the BRS before or after the AC line filter? Sometimes a leaky capacitor in one of these will cause the inductors to buzz, even if the power switch is off. I've certainly seen AT power supplies built this way.

 

[IBMMuseum]

I've seen a similiar issue with the 8086-based Model 30 PSU a few years ago. The two Model 30 versions (8086 and 286-based) share nothing as far as the case or power supply, and the 8086 version has full-sized PSU planar connections (in the style of the PC/XT/AT). There is smaller plugs on the Model 30 286 PSU, and the PSU is shared with the Model 53SLC2 and Model 55SX systems.

 

[Chuck(G)]

Take that, doubters.

Well, as a technological society, we're certainly in for surprises when we have "always on" devices. For example, there's this nightmare.

 

[kishy]

Is the BRS before or after the AC line filter? Sometimes a leaky capacitor in one of these will cause the inductors to buzz, even if the power switch is off. I've certainly seen AT power supplies built this way.

Forgive me but what is the BRS?

I've seen a similiar issue with the 8086-based Model 30 PSU a few years ago. The two Model 30 versions (8086 and 286-based) share nothing as far as the case or power supply, and the 8086 version has full-sized PSU planar connections (in the style of the PC/XT/AT). There is smaller plugs on the Model 30 286 PSU, and the PSU is shared with the Model 53SLC2 and Model 55SX systems.

I imagine the primary differences were output wattage (and of course the necessary components to change it) and connectors, with few or no other differences. I'd expect the circuit(s) inside to be otherwise very much the same, though I may be way off on that.

Well, as a technological society, we're certainly in for surprises when we have "always on" devices. For example, there's this nightmare.

Yikes, that's scary. Fortunately we have an electric stove with an...uh, I guess you'd call it analog knob you must turn on before it comes on.

 

[Chuck(G)]

Forgive me but what is the BRS?

Big Red Switch

 

[kishy]

Big Red Switch

Oh I see. In that case, what is the line filter? I'm guessing it would be a large capacitor or couple of them, but how would I pick it/them out from the others?

 

[Chuck(G)]

Oh I see. In that case, what is the line filter? I'm guessing it would be a large capacitor or couple of them, but how would I pick it/them out from the others?

Frequently, the line connector takes the form of a "can", with all of the goodies integrated inside:

It's not unknown for the innards to develop issues.

 

[kishy]

Frequently, the line connector takes the form of a "can", with all of the goodies integrated inside:

It's not unknown for the innards to develop issues.

Ohh, alright, I would just say it's probably before the switch then based on the switch being a very large distance from that assembly, but I will open it up and let you know for sure when I've got a chance.

 

[IBMMuseum]

The 8086-based Model 30 PSU is 90 watts. I think the other is somewhere slightly over a 100 watts. And in some cases, that "BRS" is a "BWS" or "BBS" mounted on the PSU, it's hidden, so IBM didn't attach too much color significance to it.

 

[kishy]

Frustratingly, IBM used a security screw for the PSU casing and I can't get into it without damaging the screws, casing, or both. It's like philips with a peg in the middle. I have the common security bits but not that one.