PSU for test

[Jidis]

More positive news on that. It does seem likely to be down to an electrical issue with some of the panel switches. There's a square opening at the rear of each one, so I blasted in some plastic-safe Home Depot contact cleaner someone recommended here, to get the mechanics functioning again, and the whole unit magically came back to life, meters and all. When I got home later tonight, the voltage doubler switches for each channel had sort of gummed back up and it was back to doing the "drop the voltage when a load is connected" thing. Tried to clean them again, but they reverted to "gunk mode" faster this time. They probably need to be removed and cleaned more thoroughly (or disassembled).

Bruce- They don't look that uncommon inside. The more well behaved two look like DPDT, but the voltage ones are those multi-pole types with a whole row of pins on each side. The footprints look like lots of stuff I've seen, so unless the switch caps or the pinning is some oddball stuff, I may be able to swap something else in there.

Question: Anybody know how to remove those banana/screw terminal combo jacks on the front without desoldering. They're the type that stops when you unscrew it far enough out, so the thumbscrew part doesn't come off.

Thanks! 

 

[bruce0]

It sounds like the current setting is very low.  Under those conditions when you attached a load it would clamp the voltage down.

Make sure you have the sense and voltage output connected on the back connectors (this is the most common problem - 3 of my psu's and a couple mentioned in this thread - with ebay PSU's because often there is a voltage sense line running to the bench and when they pull out the supply nobody reconnects voltage and sense.). 

Usually the 3 way banana jacks don't come off, usually they are not PCB mount instead they have a nut on the back of the panel that clamps them to the panel.  Have you been inside this thing?  Have you got the manual (HP manuals are available online to download and they are in general AWESOME.  Detailed schematics, step by step teardowns, board layouts, adjustment information, the works.).

 

[Jidis]

Hey Bruce,

The voltage drop on load seems to come along with the gummy switches, so I'm guessing it's due to some bad electrical connections in those hi/low voltage selector switches. When I first cleaned them today, I actually used the supply for a good while and everything acted fine. Once the mechanical issue with the switches came back, so did the dropout thing. I'll probably have to break down and remove them to see how to get them fully cleaned or measure for some new ones. I was looking to get dimensions on the electrolytics anyhow.

Thanks for the info on the front jacks. That's what I was afraid of. I saw the nut on the back, but I guess that means when you unscrew it, they need to pull out frontways which they can't do without desoldering. The main power switch has a similar looking bezel on the front, but it's threaded and there's nothing stopping the switch from being pulled out from behind after it's off.

BTW- The manual has parts lists and schematics, but the only "take apart" type stuff in there is info on rack mounting or something.

Take Care,

George

 

[bruce0]

Looked at the manual.  Pretty good but a bit light for the normal HP stuff.  It does have a PCB layout though, and the part numbers and manufacturers are listed.  HP manufactured the switches (it says).

The switches are used in setting the current limit apparently so flaky switches could put you in a low current limit.  Clean the switches or replace them.  There are spare parts listed online I searched by hp part and the number and several vendors came up (all offered to quote, no online prices.).

I am sure you have this well in hand, but in any case make sure you have it strapped in the default way.  A7/a6/a8 straps change the current limiting so make all the straps match the pic.

 

[Jidis]

Bruce,

Thanks again! Yes, the terminals were checked when I got it. The only difference from their default picture were the ungrounded '+' lines (which I then jumpered).

It's weird how those switches got gooey again so fast like that. When I first sprayed them out, they were perfectly clean with nice sharp clicks, now they're right back to drifting out really slowly and probably not making contact. I'm imagining something like that deal when old lithium grease turns all brown and crusty.

George

<EDIT> - Man, you guys seen the caps in this thing? FOUR pins. Don't see any polarity markings either, unless they're on the bottoms.

 

[Jidis]

I'm going to have to wait and remove these when I get back.

So what do I need to tear them apart or can I just soak them in something?

Thanks!

 

[deveng]

The push button switches, from what I remember when I opened up my units, are Shadow type switches.  I don't think they'll clean up easily (or at least stay good after cleaning).  When I maintained API consoles I always replaced them as cleaning was not reliable.  You can still get these switches from Digikey (now ITT Canon or  C&K F2UEE series).  They go up to 10PDT.  The 360 degree multi turn pots are another story.  Exercising them may help.  If you have an access hole in them I'd not use anything other than Caig DeOxit contact cleaners.  Even this DeOxit only works for so long but its great stuff. 

Its a positive sign that once you get good switch contacts the unit works!  Hopefully all you need to do is replace the switches and you'll be up and running.

Regards,
Jeff

 

[Jidis]

Thanks Jeff,

I'll look into finding a match when they're out, but may still clean them and try them, to make sure everything else works. I think the pots are actually OK. They're not real easy to turn, but I'm not sure what they started out like. For something which may need fine adjustment, and need to stay put, they may be best off a little bit stiff anyway. It doesn't seem to be affecting their function like the switch issue is.

Take Care

 

[Jidis]

Man, I'm wishing I hadn't even messed with this now, or had just dunked the whole front end of it in alcohol or something. Almost every pad which didn't have a trace attached to it just slid right off the board like they were never attached the moment the desoldering gun touched the pin. I don't know if it was age or all the chemicals which have been applied to that area, but it looks rough as hell now and I haven't even gotten the second channel switches off yet. I'm going to have a lot of cleaning up to do, plus I'll have to make absolutely sure that all the pins have a good connection on the top side where needed, which will be loads of fun as the switches are all side by side, blocking access to a bunch of the pins.

Probably best to see if I can match those Shadow switches Jeff mentioned now before trying to reinstall anything. I doubt this board would withstand a second attack.  :-[

George

 

[bruce0]

The picture looks like they are sealed switches.

Not sure how easy sealed switch will be to disassemble (they are silicon or glued so nothing can get in (obviously it didn't work )

 

[Jidis]

Hey again Bruce,

Here's a better picture now that they're out. The openings are on the ends. Not sure how they come apart if they do, but I'm guessing those 'U' shaped brackets on the front may have something to do with it.

I'm undecided now as to whether I'll have the patience to track down a match and wait for a parts order to come in. I'm trying to get better about not leaving stuff disassembled long enough to forget how to put it back together.

I soaked them in alcohol last night, which didn't seem to do much, then some mineral spirits. The two long ones are moving pretty well now, I'll probably let them dry, then spray them out with contact cleaner/lube and let them sit for a day or so to see if they continue to move well. Meanwhile, I'll be looking through umpteen million pages of Digikey & Mouser switches. There are some in there with an actual lead hole in the top-side pins which may help. I think to be safe, I shouldn't trust most of the pads and traces on that board now. I even had through-hole plating wrapped around a few of the switch pins when they came out. Luckily, the connections aren't that involved. I can probably jump a few contacts on the top of the switches to make sure they make it to their original destinations.

If anyone recognizes these right off, let me know. Didn't see the "Shadow" switch there (or is it Schadow?? - which they don't have either). BTW- The "C&K Components" brand at Digikey has some similar ones in their "F-Series", which includes one that looks exactly like HP's power switch.

George

 

[bruce0]

just need to check the data sheet to make sure the switch cap will fit and the spacing off the PCB is right.

 

[Jidis]

FWIW, I totally disassembled them today and actually managed to get them back together without breaking or losing anything. I took the little copper contacts out and burnished them clean and smooth with a buffing wheel in a Dremel. I also stretched those and the actuator springs out a bit to restore some of the pressure and get good connections. Only thing I'm not 100% comfortable with is the mechanism which holds the switch in the in or out position. It's nothing but a little pin which rides in a 'V' shaped groove in the actuator shaft. The groove has sort of a ramp shape inside it, and as expected, has gotten a bit chewed up over the years. Despite that, all six switches seem to have a nice click to them now that they're clean, and they stay put in either position.

If anybody ever wonders what's inside these things, maybe this picture will help. In the closeup on the right you can see some of the crud that was caked up inside them. The pins just go straight through the body of the switch from top to bottom, so if you look through the body when the actuator's out, you see them all along the walls inside. It's three pins per contact, and the contacts slide between pairs (with a center common).

Take Care

George

 

[bruce0]

The switch actuator shaft looks like the one on the F series switch.

I did some basic measure  ( but the data sheet is pretty great for those F2...2u ee whatever switches... very common)  of a switch of that type for you.

The key dimensions on these switches is usually:

1) How high the center of the switch shaft is off the top of the PCB (how high they sit)
2) How they attach.  The F series I think attaches with the will and strength of the PCB pins, which is fine except you mention that you are concerned about the PCB pads.  Some switches have brackets that hold them.  Looks like yours do too.  They don't look melted (from your descriptiong I was worried they were dissolving)
3) The shaft dimensions (square shaft with a ridge, the cap clicks into the ridge.

almost always the  side to side the shaft  position is centered.

Distance to front panel can change too.


Note that I looked at your schematic in the manual and it has a list of parts and manufacturer number.  There is a table of manufacturer numbers to names in that same manual.  It says your switches were MFG by HP, but I doubt it.  Gives a part number though, and maybe you can order it from HP. 


Here are phot's and measures (inches).

 

[Jidis]

Much thanks for the photos Bruce.

Mine seem to measure the same as yours. I can check the pin spacing and stuff in their datasheets, but I have a feeling there's a ton with those same specs. Whose switch is that you've got anyhow?

2) How they attach.  The F series I think attaches with the will and strength of the PCB pins, which is fine except you mention that you are concerned about the PCB pads.  Some switches have brackets that hold them.  Looks like yours do too.

Yeah, I was thinking about that when I was out. It is a problem, not only for the stability, but for the connections. On the bottom side, the four small switches have probably only got a couple pads each which are still intact, and I'm not even sure I can trust them. As much as I hate to do it, I may need to resort to a blob of glue or something to anchor them somewhere. I'm not sure what exactly that bracket is about, but it seems to be custom cut to the number of switches you have. Don't know if that's a separate part you order, or if I can do without it. It has some tabs on it which you bend down slightly to lock it onto the switch body, so I doubt it's interchangeable from one manufacturer to another.

They don't look melted (from your descriptiong I was worried they were dissolving)

No, about the only thing which seems worn on the shaft parts is that little 'V' indentation I mentioned, but like I said, it still seems to work OK.

It says your switches were MFG by HP, but I doubt it.

Even if they were, I don't see any reason to stick with them. I saw an Agilent price list for some of the stuff you can still get, and those front panel binding posts were $21 each or something (for the red one - the black one was *only* 13 or so ...go figure). BTW, the top switch pins almost look like they've been snipped by something. I'm wondering if they had those solder lug things at the top and HP cut them.

Take Care

George

 

[bruce0]

I have no idea if there is any similarity between the brackets.  I don't think so.  You would be lucky if they fit the new switches. 

I know that jeff at classicapi.com carries them, I have different switches from different sources some salvaged.  But I think the sealed one was from Jeff and he has datasheets, and is a good guy might be able to help you out figuring it out.

The HP switch looks like a more solid thing that these, but they are fine.  Of course I don't know the amps etc, but it is spec'd in the schematic, I think it is ... Probably fine.

With plated through holes or really large pads securing the switch with pins and pads works, as the board quality goes down (as it sounds like you have a problem with) not so much.  The brackets make that better. 

Why can't you use the existing switches?  If they are "degunked" and staying that way.

 

[Jidis]

Why can't you use the existing switches?  If they are "degunked" and staying that way.

Funny, I've been doing everything in my power to convince myself not to for the past twenty minutes. I had all but decided to go ahead and get some cheap replacements before I read your post. Now I'm back to thinking about using these.  8)

All poles check fine for continuity with a multimeter, except one stupid side of one of the small switches. I've now disassembled it at least three times and don't see the problem, but knowing what I do now about how they work, I may be able to get it going. Ironically, the two long ones seem to be functioning perfectly. They're the ones which were acting the worst before I started.

Just in case I do go back to looking at replacements, would you by any chance know what some of C&K's options mean for "mechanical function". They've got: Momentary, Alternate (push-push), Interlock, Central Release, Momentary with Lockout, and Interlock with Lockout. The "Alternate (push-push)" seems to be the most common one, but I can't tell if that means it stays "in" when in the "in" state. Interlock sounds more like what we're used to, but I don't even think they stock those, so I'm guessing it's something weird.

Thanks,

George

PS @All - If you ever need to mess with one of these switches, make sure to do it on a well lit surface, arranged so that nothing can escape, fly out, fall to the floor, blend in with surroundings, etc. 

 

[bruce0]

I don't know about interlock, but I think you want alternate push push.  I think this is  push it once, locks in, push it again pops out.  But this is just a guess.

 

[dfuruta]

Interlock on these switches is when you put a bunch of them next to each other, and when you push one in the others pop out.  So, you can only select one out of a group of settings at a time (like on a bench multimeter, when pushing in the volt button pops out the current button, or similar).

 

[Jidis]

Thanks guys! Yeah, I've got a bunch of those Interlock types on an old DJ mixer/processor combo here, but had never heard that term. I suspected Alternate was most likely the one I need. I'm going to go back into that malfunctioning one today and see if I can get it working though. I've got a feeling 95% of the units out there still have the original switches in them and have never even been "de-gunked".  ;D

Take Care