Source of growling from Philips PM2525 DMM

[watchmaker]

The source of the growling is the plastic contact wiper that is driven by the motor and gear.  I took the motor out and it ran quiet with no vibration.  There are tapped holes in it that line up with holes in the ckt so I found two screws and screwed it to the board (loctite on threads).

It WAS held in place only by the plastic wiper/motor shield.  Looked at the teeth on the pinion mounted on the motor, and the sections at the end seemed misshappend.  Move the pinion to get a good section to mate with the driven wheel.

Checked for free rotation and felt good.

Then I looked at the contact wiper and the contacts.  You can see chatter marks on the contacts.  The wiper vibrates like hell when searching for the null position which defines the selected function.

The driven wheel is keyed into a bushing that is part of the contact arm.  Everything is delrin, pinion, driven wheel, contact arm, and bushings thru the board.

I cleaned the contacts and adjusted the wheel and contact arm to provide some contact pressure w/o overloading the motor.  Takes some fiddling to find a  happy; but not perfect spot.

Still makes noise, but it is less.  I think the vibrating contact arm vibrated the entire protective shell which vibrated the motor against the board.  But I think without resurfacing the contact strips themselves, the vibration from the search will always be present.

My guess is that they intended to replace the motor/contact arm as an assembly when it got to this point.  Kind of like dealing with a dying VFD.

Dewey

[coppercone2]

did you put grease on the PCB? it looks dry. typically on meters you put some grease on the gold pads so it runs smooth and the contact is better

[coppercone2]

the only thing that bugs me is, does the gear get mounted to a bushing on the PCB or is it exterior? While the force is low, I feel like gears anchored to a PCB with parts on it is... kinda bad. well through hole its probobly more then OK

[watchmaker]

Huh.  Grease??  What kind?  I will look to see what the SM specifies as well.  I saw no evidence of old grease, like tracks or discoloration.  Thanks!

I will take the driven gear back off when I reassemble this.  It is mounted on a long post that is keyed into the wiper arm "tube" and it has a snap connector on top to lock it in place.  That wiper arm tube is a machinist's "loose fit" thought the PCB.  Delrin and phenolic should produce little wear in the absence of dirt and little friction.

It is obvious someone tried to get it it before me me.  Two of the snaps are broken as seen in the photo.  Also the cover (which is used to keep the gearing depth correct (kind of)) is used to hold the wiper/driven wheel assembly and the motor located.  That cover had two out of three push connectors broken. 

Plus one side is split.  As found, all of these are sources of vibration (hence noise).

Also, at 3.1 V, the cal battery must not be 40 years old.  At this point, might as well check the adjustments against my other DMMs which all agree w/in the last digit.  (I was known for my results in the restoration of precision timekeepers).

Moving into this because my hands are shaking and when I use the scope at even 30X all I see are the floaters in my eyes.  I don't get that last bit, need to look up what is happening optically.  But now I only do marine chronometers and aircraft clocks.  And the time will come when I cannot be trusted with those.

Interesting piece of tech equip history.  Is it worth $200?  I do not think so.  For function, the Fluke 8088 or HP 3478a are better choices; even though the PM2525 has capacitance and freq (everyone has a component thingy).

The motor can be replaced (the contacts establish position so there are no issues when the assembly is taken apart) but mine is doing just fine.  But that jiggling of the wiper arm may be the source of the chatter marks on the contacts.  Or, the chatter marks may be the source of the jiggling because of changes in current.  The grease may help here.

I would presume that in such a premier piece of TE, Philips would have ensured the contacts were polished almost optically flat.  This was standard machine finishing back in the 1940s.

For completeness of those following breadcrumbs, mine was fully shielded.  Both top and bottom.  I will include a set of pics in this thread.  I am old and therefore have only done one Youtube and that was to describe the restoration and  function of a rare seconds jump escapement which Omega USA will not touch and sends back to Switz.

So pics and website are what I do.  Even that was built and is maintained by Front Page 98!!!

I wrote about the history of tech in watchmaking (including the search for the perfect mechanical oscillator)
and built a collection around the evolution of industrial watchmaking (btw, the three founders of the Hamilton Watch Co. preceded H. Ford by 10 years).  I got rid of my Simpsons specifically to avoid the temptation to go down that rabbit hole in this area.  And tubes take up way too much space.

OOPS.  Got off a bit on a tangent.  Apologies to anyone highly goal directed.

[abeyer]

such a premier piece of TE

It's a premier piece of something... but I might have chosen another word. 

This whole series was kinda meh overall, even aside from the weirdness of the motor driven selector in the low end model. Overall specs are not really all that great for what they are, and there are plenty of downsides to them. The one big upside seems to be that they seem not to fail often and you can still find them cheap on ebay in pretty good condition, if you're willing to put up with all their quirks.

[coppercone2]

idk slide switches and crimp/connectors work better with grease you got a metal on metal contact.

there is alot to read about this, but typically people will at least put a smear of vasoline or something on a multimeter contact. its not a watch, your not gonna bog down a mechanism, it reduces fretting/friction and typically improves the contact since the grease is thermally conductive

the only time I get paranoid about grease and electronics is on non solid coaxial cables since they might wick, especially the tape wound microwave type.

Different story for switches, that is up for debate.. (I won't do more then oil)

my welder IGBT goes as far as having like a jelly on top of the dies, then there is a buncha contacts that push through the jelly into the contact pads (miller welding machine). I bet it would do pretty poorly without it.

in all likelyhood the telephone system would be total shit without silicone grease filled IDC's

ideally the contacts would be submerged in something, air does nothing good for them, unless they need to haul ass... this is what the telephone company does with silicone grease, and IGBT get like a jello on top (thicker then grease).

you only have problems when things are either mega low force contact or get slowed down too much. a reed relay is something that probobly should be totally clean. A regular relay... not sure. might need redesign of the armature for lower fluid friction ... but they have special oil filled relays and switches that can take much more power.

but your problem is friction and metal on metal side wear

people freak out when you put grease on gold btw, but its still a metal

[J-R]

There are plenty of opinions here on the forums about lubricating contacts.  Even the top tier manufacturers have some DMMs with and some without.

Personally, I have disassembled all of my DMMs and the ones without grease all show signs of material being worn off so now I always apply something if there isn't any there.  If the lubricants cause an issue down the road, I can just clean it off, but replacing worn parts isn't so easy.

What to apply is also a big debate.  I don't like the idea of Vaseline as it is thick so could interfere with contact surfaces, but also has a low melting point which means it might move around to other areas.  I also have concerns about long term stability.  But again, it's easier to clean things later than to replace worn components.

For electrical contact surfaces, personally I start with CRC contact cleaner first.  Then I apply a light coating of CRC 2-26 for lubrication.  It's more like an oil than a grease.

For other non-contact portions of moving surfaces, I use a small amount of Super Lube Synthetic Grease.

Once given the above treatment, my DMM selector switches are so much nicer to use.

[watchmaker]

I thought about this and decided against it.  Yes, I use CRC Contact cleaner routinely.

My reasons against this are that there was no evidence of lubricant on the contact plane, nor did the SM indicate lube when replacing the contact assembly.

Also, upon reassembly (motor screwed down, good "shake" (up down movt of the contact assembly), and reinstalling the cover, it was as quiet as a cat purr.  And it functions correctly.

Adjusting the shake on the contact assembly is tricky.  Too much and the wiper vibrates, too little and the motor drags.

Grease would not be a good choice and the CRC seems to have done the job.  I do not know enough about the DeOxit line to go ahead and buy some, but the liquid would likely work.

This DMM is interesting.  The cover for the drive assembly was apparently a production change given the the presence of mounting holes for the motor.  My guess is that the original plan created problems for proper depthing of the pinion and drive wheel.  So the cover was designed to locate the motor and contact assembly.  Still does that with motor screwed down to eliminate vibration.  The cover may also have been intended to isolate the drive assembly from the PCB.

The source of acoustical noise is that the motor is driven in steps (37 Hz and 53 Hz).

The contact assembly is keyed, excessively so since the positioning is accomplished by a series of motor switch pads that correlate to the selected function.  This means it can be assembled without worrying about alignments.  Ingenious.  But the excessive keying added unneeded tooling expense.  Belt and suspenders.

The instrument is completely shielded.  The enclosure is dustproof with no ventilation.

So it was designed for no heat build up in an era when no one cared about lost electrical energy.

The power switch is in the back and somewhat of a pain to use.

What was the market?  Not rack oriented stations.  Service grade?  With all the other functions?

As for its specs, for the time (mid 1980s?) it seems it would have been viewed as pretty high class.  Especially when you add functions like freq, capacitance and temp.

But as far as value today (other than as an artifact), I do not see it as anywhere worth $200 or even $50 when compared to a Fluke 8840/42 or HP 3478a that can be had for under $100.  If you need a DMM that displays Freq, the Fluke 45 is a better choice.  And the $20 thingys that test all sorts of components make the capacitance function irrelevant.

As an artifact, it is useful to hold onto.  Where the iconic Simpson 260 will never be worth much (far too many made and surviving), given how rapidly things changed, I doubt this was made in very large quantity.

I will upload photos later today for those looking for info on this meter.

[BILLPOD]

Good Morning Watchmaker,  I am well into my seventh decade on this earth and I must have lead a sheltered life, because I had never heard of a multimeter with a motor in it.   I naturally had to Google it, and photos show plenty of push buttons on the face, so the reason for the motor seems strange.   Oh well.....live and learn.  Thanks for sharing your experience with it.

[watchmaker]

Good Morning Watchmaker,  I am well into my seventh decade on this earth and I must have lead a sheltered life, because I had never heard of a multimeter with a motor in it.   I naturally had to Google it, and photos show plenty of push buttons on the face, so the reason for the motor seems strange.   Oh well.....live and learn.  Thanks for sharing your experience with it.

At least two of us appreciate old things!  Maybe it is a defense mechanism?

Anyway, here are the rest of the pics.  The drive cover is located into the ckt board via three expansion  pins.  The motor is a tight fit into the case, and the wheel/contact assembly is located with by the expansion pin showing thru the motor cover.

I failed to take a pic, but the contact wiper position is communicated by a set of contact pads on the outer most ring of the contacts on the board.

A lot of ingenuity and engineering into this unit.  It most definitely was not designed to compete with Simpson or Triplett and is deserving of respect.

I did find a seller of a SM CD on eBay.  It has about 50 more pages than the copy circulated on the internet which is missing the most important stuff (calibration and schematics).  I took gamble for $10.

[shakalnokturn]

This DMM is interesting.  The cover for the drive assembly was apparently a production change given the the presence of mounting holes for the motor.  My guess is that the original plan created problems for proper depthing of the pinion and drive wheel.  So the cover was designed to locate the motor and contact assembly.  Still does that with motor screwed down to eliminate vibration.  The cover may also have been intended to isolate the drive assembly from the PCB.

The source of acoustical noise is that the motor is driven in steps (37 Hz and 53 Hz).

I've been working on one of these, I copied your modification by screwing the motor to the PCB, on mine the holes were not pre-drilled although the solder mask was missing where they could have been.
Here too the gears were engaged just by the skin of their teeth and even then not on the whole height, so I decided it was worth the bother just for that.

Came to the same conclusion on the growling, it isn't directly mechanical but more the low frequency pulse drive (the service manual states 32/56Hz), of course making the switch assembly smoother doesn't harm.
Not much hope of making it silent easily, if I planned to keep this meter I'd probably use a small microcontroller to sample the motor pulses out of the 74HC27 (D1705) and PWM the existing H bridge at a higher frequency.

Does your paper CD copy of the manual give the full schematic?

Edit: Added photos and EPROM dump, apparently different from the one found at KO4BB's archive.

[watchmaker]

This DMM is interesting.  The cover for the drive assembly was apparently a production change given the the presence of mounting holes for the motor.  My guess is that the original plan created problems for proper depthing of the pinion and drive wheel.  So the cover was designed to locate the motor and contact assembly.  Still does that with motor screwed down to eliminate vibration.  The cover may also have been intended to isolate the drive assembly from the PCB.

The source of acoustical noise is that the motor is driven in steps (37 Hz and 53 Hz).

I've been working on one of these, I copied your modification by screwing the motor to the PCB, on mine the holes were not pre-drilled although the solder mask was missing where they could have been.
Here too the gears were engaged just by the skin of their teeth and even then not on the whole height, so I decided it was worth the bother just for that.

Came to the same conclusion on the growling, it isn't directly mechanical but more the low frequency pulse drive (the service manual states 32/56Hz), of course making the switch assembly smoother doesn't harm.
Not much hope of making it silent easily, if I planned to keep this meter I'd probably use a small microcontroller to sample the motor pulses out of the 74HC27 (D1705) and PWM the existing H bridge at a higher frequency.

Does your paper CD copy of the manual give the full schematic?

Edit: Added photos and EPROM dump, apparently different from the one found at KO4BB's archive.

Sent you a PM.

[coppercone2]

I am curious about your beliefs about moving surfaces and grease.

I was reading about gold coatings.
1) A hard gold coating (chemical) is rather tough and this is what lets you get away with unlubricated connectors in electronics. However SEM pictures reveal that there is scraping (and also gold dust formation) upon contact mating, just a acceptable amount within the number of insertions in the specification. There is a bit of nickel or something distributed in the chemical gold electroplate that makes its hardness drastically rise compared to soft gold plate.

2) In an attempt for environmentally friendly gold coatings, the layer deposited is soft gold  electroplate (pyrite based chemistry (I think this is sulfur rather then CN. It only deposites gold and can't put the Ni mixed in the deposition)). This one experienced greater wear on insertion. In an effort to make this process acceptable, they studied lubricants. It was determined with a lubricant this plating could experience less wear, still more wear then the hard gold plate but it offered acceptable cycle life numbers for the specification. This was shown as less cratering/trenching on SEM scans. (or was it TEM?)

In both cases the wearout mechanism is that there is excessive trenching/cratering from repeated friction events. The industry does not like lubricant for process cost reasons.


Anyway, regardless, #1 would do better with lubricant. I don't see a reason why someone would avoid using lubricant on metal to metal contact, especially in a fairly closed system. The fancy microscope pictures reveal its similar to plowing a dirt field. A harder plating is more resistant to wear but oil helps.

This was for some card edge connector or SD card or maybe foldy crimps.


The parameter that can be used to track ware without a microscope is to measure contact insertion force repeatability precisely. The more deviations you have the more roughed up it is.

[watchmaker]

In watchmaking parts are not lubricated unless absolutely required to create a fluid barrier.  Lubricated parts attract and collect dirt and tiny swarf which then adds to abrasive wear.  All this is empirical and is verified by research in Switz.  We do have greases that are used in high pressure locations such as found in chronographs.  We also have an oil designed to be slippery et resist the pressures found on the pallet/escape wheel of the lever escapement, but this requires parts treatment with Epilame.  We do not oil the runners in a chronograph because of the collected swarf/debris/dust etc and the likelihood of stoppage at this low level in the train.

Better to prevent debris from getting in which is why case sealing is so important.  In the case of the PM2525, I presume that was a consideration in the decision to use a housing over the switch.  It both locates the motor pinion and contact wheel while providing a seal around the contacts.

Then, I saw no evidence of a lubricant.  No traces, no tracks. 

Having said that, I am here to learn a brand new field of interest.  So what I know may not apply.

[coppercone2]

I could see that maybe in a watch where there is basically little high speed turbines and stuff its like a pinball machine so debris can get knocked into things but for a single simple rotating object that is also not in motion like a watch on a hand I have my doubts that there will be increased wear for this reason compared to the plowing (high pressure dramatically reduces the contact resistance if it is important in this application).

[watchmaker]

I could see that maybe in a watch where there is basically little high speed turbines and stuff its like a pinball machine so debris can get knocked into things but for a single simple rotating object that is also not in motion like a watch on a hand I have my doubts that there will be increased wear for this reason compared to the plowing (high pressure dramatically reduces the contact resistance if it is important in this application).

Well, even though  I am not the brightest bulb in pack, I know enough that practice in one area is not necessarily generalizable to another.

I am here to learn and if the industry practice is to lubricate these switches, then that is what I will do.  What is the proper lubricant?

THANKS!

[coppercone2]

I don't know. I know people have concerns with the cleaning of silicone grease. If I don't know I use fader lube grease form from deoxit. That one does not have any cleaning chemicals that seem to worry people and it lubricates enough IMO.

otherwise I use deoxit grease loaded with cleaning chemicals. Pretty tough stuff I rubbed a bunch on my welding table and it only got minor damage from acid splatter during my brush electrocleaning experiments when stuff got out of the tray. I am sure it would be super wrecked without.

NYOGEL is something people use industrially for crimps etc.

Fader lube grease comes in a small container and it has the consistancy some where near warm chapstick, I don't see it wicking too much.


But anyway, the contacts are gold, nickel and bronze underneath. The circuit board is epoxy laminate, all super unreactive. IMO the biggest concern is that
1) it lubricates
2) it does not wick (non 'penetating') to make a mess
3) does not react with potentially cheap plastic (body of the rotating thing probobly)

so long life plastic safe grease

[coppercone2]

https://caig.com/product/deoxit-fadergrease-dfg-213-8/

It's meant for moving contacts on conductive plastic. While these are not plastic, it must be pretty darn plastic safe if its meant to be used on weakened plastic optimized for conductivity. Also non reactive. That is the only I have that I would use if I had any concerns about like problems

but again, if you have some kind of concerns about silicone, then I don't know. Maybe just red home depot car grease or something. But petroleum grease dries out etc. Maybe lithium grease of some kind there, but I have no experience with this.

I think your options are either petroleum (which might have improved life with additives) and might effect plastics or silicone based that have greatly increased life but might be hard to clea. I think these re mostly naphthalene based. They get mad tacky when old though. I would not want to stall a motor if its been dormant for 10 years.


Silicone based is the industry standard for tons of stuff including telephone switches, crimps, grease sealed stuff, etc. I think its only a concern if it gets inside of arcing high current relays. I think the fears of it are caused by wicking light silicone oil that manages to get into arcing contacts and glasses them, on satellites. 

[Jwillis]

You never want to use petroleum based lubricants of any kind on plastics. It's not that on some plastics petroleum based lubricants would be fine, but it's the uncertainty of what plastic your using. Silicone based lubricants are  safe for all plastics. You need to be careful of some lithium greases because some are plastic safe and some are petroleum based. Mechanics lithium assembly grease  is petroleum based in most cases and White Lithium grease is bad for nylon. Another problem with petroleum based greases is they dry out and become gummy.
The dielectric grease is best for all electronic mechanical mechanisms, doesn't dry out, higher temperature rating than petroleum based, and can be found in food grade as well. 

On your motor, did you check for any lateral play on the armature shaft? Lateral play can cause a binding on the bearing/bushing which cause the armature to bounce from side to side. This makes a horrible grinding or buzzing sound on electric motors. Because of the wear, lubricants push out easily and the bearing becomes dry and  the noise starts again.

[coppercone2]

lol also there is a trick with some motors like my die grinder if its making a noise drop it on the shaft directly from a small distance to tap everything together. I thought I broke it but a bit of gentle beating in direction of the axis made it run fine (for many hours of operation after), think battering ram