POWER DESIGNS PRECISION POWER SUPPLIES

[bitseeker]

I guess they were cutting back on the cost of printing manuals even more than slipping in the R version. In the one you linked to, they just inserted a note, "Where reference is made to models 5005R and TW5005 in Section 1 and Section 2 of the following manual, substitute model numbers 5005T and TW5005T."

[SharpEars]

I guess they were cutting back on the cost of printing manuals even more than slipping in the R version. In the one you linked to, they just inserted a note, "Where reference is made to models 5005R and TW5005 in Section 1 and Section 2 of the following manual, substitute model numbers 5005T and TW5005T."

"All instructions in this manual apply equally to the Model 5005R and to both sections of the model TW5005T."

I had to fish through it to make sure it applies...

[bitseeker]

Yeah, there are so many models of PD supplies and then variations of them to boot.

[SharpEars]

Yeah, there are so many models of PD supplies and then variations of them to boot.

I got this one for a song, because it's older than dirt and is lacking remote sense. I just hope I can get the thing to work. I'll probably wind up using it to "burn in" 5 ppm resistors and voltage references into the thousands of hours of on time range. That's pretty much all I use my PD supplies for - a damn shame.

[bitseeker]

Cool. It should clean up nicely too -- not all banged up like some I've seen.

[SharpEars]

Cool. It should clean up nicely too -- not all banged up like some I've seen.

I'll post pics after I get it to work and clean it up.

[SharpEars]

How do you clean the big old pots on these things. I am getting voltage spikes up the wazoo trying to adjust the voltage setting. Do you have to actually open them up and spray them?

[SharpEars]

How do you clean the big old pots on these things. I am getting voltage spikes up the wazoo trying to adjust the voltage setting. Do you have to actually open them up and spray them?

Any thoughts?

[bitseeker]

Are you referring to the Bournes multi-turn pots? I had a busted one in my TP340A and tried to fix it, but the contact inside is fiddly and never behaved correctly at the limits. So, if you do open one to clean inside, it may or may not work correctly afterward. It might be OK if you just pop the rear cap off to flush it with contact/electronics cleaner.

I don't know what the single-turn pots are like inside.

[SharpEars]

Are you referring to the Bournes multi-turn pots? I had a busted one in my TP340A and tried to fix it, but the contact inside is fiddly and never behaved correctly at the limits. So, if you do open one to clean inside, it may or may not work correctly afterward. It might be OK if you just pop the rear cap off to flush it with contact/electronics cleaner.

I don't know what the single-turn pots are like inside.

Yep, I'm talking about the multi-turn pots that are some two inches in diameter and quite thick. I see that there are metal tabs in impressions holding the metal back to the sides and was wondering if I need to deform these tabs to take the back off and then flush the insides with potentiometer cleaner. Or, is there an easier way to pop the rear cap off or do this without any disassembly of the pots?

[bitseeker]

The housings on mine were all plastic. No metal tabs.

I haven't yet opened my 2010 precision supply, but it might have one like you describe since it's older than the TP340A. The other PD supplies I have use single-turn pots.

[bitseeker]

I see that there are metal tabs in impressions holding the metal back to the sides and was wondering if I need to deform these tabs to take the back off

That sounds very similar to the all-plastic pots. See if you can lift each tab without permanently deforming it and ease the cover off in order to minimize hardening the metal.

[eas]

I think someone (robertz?) mentioned that he drilled one or two small holes in the ends of the pot housing, used a syringe to inject contact cleaner cleaner, blew it out with compressed air, repeated if necessary, and then added some electrical lube through the same holes.

[SharpEars]

Well I opened up the Power Designs 5005R  in an effort to repair it. Let me start by giving you some background:

This model is fairly old like most Power Designs supplies and has a low granularity (coarse) single turn voltage knob (0-50V) with a higher precision single turn 0-1 V control knob inside of it. Inside the unit, there are two pots piggy back mounted with the fine on top and the coarse on the bottom. It was a real bitch trying to separate them to clean them. The two pots are wired in series and the sum of their resistance is presented to the voltage regulation circuit.

Now, the problem presented itself when I tested the unit. Because all of these analog pots are older than dirt, tiny crap inevitably got inside of them. The result of this is a very VERY serious problem. To make matters worse, the main voltage control pot is not wirewound. It has a solid circular (ring) resistive metallic (or more likely ceramic because it's a Cermet pot) element inside and offered (notice the past tense here) seemingly true contiguous adjustment. Unfortunately, because the thing is older than dirt, crap managed to get inside of it, whether it's the lube used to lubricate it (and there's quite a bit in there) or metal/ceramic dust from too many turns or the environment (or whatever). So, when the wiper (which is tiny and barely makes contact with the resistive element) gets dirt between it and the smooth track, guess what happens? Basically, you get a "break before make" open circuit scenario telling the supply to shoot a full fifty volts to its output terminals. So, any reasonable circuit you have connected, save for your current limit setting, gets instantly fried. This made me appreciate modern digital circuits with rotary encoders providing inputs to microcontrollers (i.e., solving this entire problem).

I first noticed the spikes when I tried to test the supply through its entire 50 volt range. As I turned the coarse voltage control pot from 0 to 50, I saw occasional brief spikes to 50 V along the way. More surprisingly, the fine tune control (which has a wirewound pot backing it) also caused spikes. This behavior makes the supply not only useless, as is, but also dangerous, both to DUTs and small furry animals. One can argue that you can set the voltage first and then connect a circuit or device, but I feel that this is too much to ask and a mere touch of the voltage control pot can shoot a 50+ V spike (i.e., infinite resistance in the regulation circuit) through the device connected to it, because a single grain of crap got under the wiper or it (i.e., the wiper) left the resistive element for ten milliseconds due to vibration and tight tolerance (combined with a crap speed-bump it was balancing on partially).

I tried to take the pots apart and clean them, but this was futile. The things are just way too old and the tolerances too tight inside. They were never meant to be taken apart and cleaned. There's lube inside and the wiper is at such tight tolerance with the cermet track that any shift when it is taken apart will result in more of that "break before make" action when put back together. It's just not worth the effort and danger. I certainly would not trust any sort of "drill holes, blow and clean solution," because even if it works perfectly on day one, all it takes is for a single particle to get in between the wiper and track and your circuit under test is literally toast.

So, the solution to the dilemma was to take a single 10 kOhm Chinese Bourns imitation 10-turn pot and replace the two (coarse and fine) with the single multi-turn pot. Sadly, the hole in the metal front panel was too small and I had to drill it slightly larger to fit the fake Bourns pot. The whole endeavor including removing the old pots, examining them and mounting the fake Bourns took about two hours.

In the end, this seems to have worked fine and allows, with some manual dexterity, adjustment on the order of about 5-10 mV. Also, there is no longer a "break before make issue," because with a new non-corroded, non-polluted wirewound pot, it's always "make before break." My only concern is not knowing how many watts of power are being placed through the pot itself to make sure that this is within the 0.6 W or so that it is rated for. In a conventional voltage regulator circuit, the current flowing between the Adj and Out pins is tiny. In this particular supply's circuit, who knows...

I have two TW4005 dual-supplies I got recently that need similar treatment due to the same voltage spike issue when the coarse control is turned. The bottom line is that unless you are willing to replace the pots on Power Designs analog supplies that use pots for regulation (i.e., the non-precision supplies), they are a bad idea (to buy). Even on the precision units, you absolutely must properly clean the switch contacts for them to work properly and without danger. All it takes is one open circuit caused by "crap interference," even in a switch designed to make before break, and you can kiss your DUT goodbye.

[mtdoc]

So, the solution to the dilemma was to take a single 10 kOhm Chinese Bourns imitation 10-turn pot and replace the two (coarse and fine) with the single multi-turn pot. Sadly, the hole in the metal front panel was too small and I had to drill it slightly larger to fit the fake Bourns pot. The whole endeavor including removing the old pots, examining them and mounting the fake Bourns took about two hours.

In the end, this seems to have worked fine and allows, with some manual dexterity, adjustment on the order of about 5-10 mV.

Hey, waaaiiit a second.  Didn't you raise a ruckus about these fake pots, contact the FTC, Bournes, etc to try and prevent them being sold.  Now it turns out (no pun intended) that after getting a refund, one of them was used to fix your power supply.  What the ..

[SharpEars]

So, the solution to the dilemma was to take a single 10 kOhm Chinese Bourns imitation 10-turn pot and replace the two (coarse and fine) with the single multi-turn pot. Sadly, the hole in the metal front panel was too small and I had to drill it slightly larger to fit the fake Bourns pot. The whole endeavor including removing the old pots, examining them and mounting the fake Bourns took about two hours.

In the end, this seems to have worked fine and allows, with some manual dexterity, adjustment on the order of about 5-10 mV.

Hey, waaaiiit a second.  Didn't you raise a ruckus about these fake pots, contact the FTC, Bournes, etc to try and prevent them being sold.  Now it turns out (no pun intended) that after getting a refund, one of them was used to fix your power supply.  What the ..

Yep, you are right. It just so happens that this 10k version I bought knowing full well it's a fake, it wasn't advertised as genuine and came with a ten turn indicator (and I had to pay $1.50 for shipping). So, the seller didn't really lie about anything in the listing, although it does say Bourns on the back of the pot. If you look carefully at the link to my prior post that you yourself provided, you will notice that the items pictured were 2k pots (1k and 5k units were also part of that purchase).

I didn't refund this 10k pot, since there was no pre-conceived notion or advertisement of authenticity and therefore I felt no desire in making the seller refund and take a loss. If I really wanted to pursue this, I could have easily gotten a refund under eBay's "no counterfeit goods" policy, but I am fair to sellers that don't make false claims in their listings, even if they still sell counterfeit "junk" for counterfeit junk prices.

So far, the pot is working pretty well. I don't expect it to last through 100,000 turns though...

My goal in the prior post was not so much eliminating the fakes off of eBay, it was about punishing sellers that market fakes as genuine/original goods and/or post BS specs that are not even remotely accurate. Those are the ones I go after when I feel like "making them pay for scamming us." Counterfeit good will always be sold, but claiming they are originals, that's where I draw the line on punishment. The "notifying the FTC and Bourns" were just scare tactics used on the seller when he insisted they were genuine and wanted me to send them back at my cost. Of course if he persisted, I would have definitely sent all the pics and info I collected to eBay and would have still gotten a refund, as I did with the boost converters mentioned several pages down in that forum post when the (other) seller began to act like an ass.

[mtdoc]

It's all good. I was just tugging on your (Sharp)ears. 

[Joule Thief]

I have a PDS 5005 coming next week to add to the bench. I will be on the lookout for noisy pots.

I just refurbed an older HP 6113A displaying noise while setting the output voltage with the 0 - 100 uV control.

Upon disassembly of the control (pic below), dried lube was the culprit. The dried lube cleaned off easily with IPA and a light coating of Rheo-Lube returned the performance to being repeatable at the 10 uV level. I hope the PDS supply is just as accessible

 

.

[Vgkid]

So who on here bought the 2020(B???) on ebay?

[SharpEars]

So who on here bought the 2020(B???) on ebay?

That was a very good deal on it. If I didn't have one already, I might have jumped on it. I am not too big of a fun of it now that I have one, because the 1 million and 1 switch contacts take forever to clean and they do need to be cleaned.

[SharpEars]

I have a PDS 5005 coming next week to add to the bench. I will be on the lookout for noisy pots.

Cermet pots are a whole different ball game, one dust particle = "infinite" voltage through your circuit... If you do get a 5005, please report back on what you did.

[Joule Thief]

I have a PDS 5005 coming next week to add to the bench. I will be on the lookout for noisy pots.

Cermet pots are a whole different ball game, one dust particle = "infinite" voltage through your circuit...

Maybe we should look into design and construction of an add-on (or add-in) adjustable crowbar over volt protector for the smaller, higher voltage PDS supplies?

a "micro bar" to borrow from an EEV Blog theme.   


http://www.onsemi.com/pub_link/Collateral/MC3423-D.PDF


I know Lambda used to offer these as an attachment to be bolted on to the rear panel of some models of their supplies.

https://www.surplussales.com/Semiconductors/pdf/ps-lmov-2.pdf

[SharpEars]

I have a PDS 5005 coming next week to add to the bench. I will be on the lookout for noisy pots.

Cermet pots are a whole different ball game, one dust particle = "infinite" voltage through your circuit...

Maybe we should look into design and construction of an add-on (or add-in) adjustable crowbar over volt protector for the smaller, higher voltage PDS supplies?

a "micro bar" to borrow from an EEV Blog theme.   


http://www.onsemi.com/pub_link/Collateral/MC3423-D.PDF

Or just do the sensible thing and not attempt to repair pots that cannot be repaired/cleaned reliably. Put in a multi-turn Bourns pot (or fake version thereof) like I did and be done...

[Joule Thief]

In the "good old days". some pots had multiple contacts on the wiper element in attempt to avoid this scenario.

[bitseeker]

So who on here bought the 2020(B???) on ebay?

Is that the one that was looking a bit long in the tooth and had mismatched dials? Wasn't me. Although I'd like to "upgrade" my 2010 by getting a 2020B, the aesthetics matter too and I didn't want to deal with mismatched parts.