Author Topic: POWER DESIGNS PRECISION POWER SUPPLIES  (Read 263389 times)

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Offline timb

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POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #325 on: October 11, 2014, 09:16:37 am »
Holy crap, that sounds like a Super Darlington! How big we're those UPS units? 4 car batteries, must have weighed a few hundred pounds between that and the heatsinks, right?

2020B Update:





Holds regulation perfectly (less than 90uV output ripple) and the voltage is spot on to +/-5uV, which is crazy good considering it came to me non-working and I haven't even touched the cal controls!

I'll leave you with 6.5 digits of pure sex:




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« Last Edit: October 11, 2014, 09:40:51 am by timb »
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Online SeanB

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #326 on: October 11, 2014, 11:44:58 am »
They were 2kVA minimum units, with moving involving either a forklift or a really strong trolley and 2 people minimum to lift onto the trolley. Around 200kg of steel alone, with another 10kg of copper, and the 2 1m long heatsinks as well inside.

Most faults had a similar symptom, no working and breakers tripped ( 63A DC bus breaker), and you would find 20 transistors minimum that had delidded themselves, or which had blown a hole in the lid. Plus the internal 80A fuse would also be blown. Most common cause was dead drivers on the main board, or dry joints there, or the PCB traces going open circuit, or all three and dead caps for good measure. They use 100uF 500VAC motor run caps on the output to filter the output, so had a low distortion real sine wave, at the expense of being also a room heater.
 

Online David Hess

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #327 on: October 11, 2014, 03:05:59 pm »
I have a question about the 2N3773.

I have old data showing it with a minimum Ft of 200 kHz and the current On (Motorola) datasheet is consistent with that but the Central Semiconductor datasheet says 4.0 MHz and the STM datasheet does not say but does mention a planar process which implies 4.0 MHz instead of 200 kHz.

Is this like the situation with the 2N3055 where the original process used (epitaxial base) was slow but rugged and it was replaced with a newer one (planar) that was fast but had a smaller SOE?
 

Online SeanB

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #328 on: October 11, 2014, 03:47:41 pm »
Yes planar is generally an order of magnitude faster, but if the die size is not shrunk then SOA would be pretty much the same, as it is a function of current density in the silicon. To meet the  label specs the device has to be equal or better than the JEDEC spec for the particular original manufacturers device. This often means the original device specs may be well exceeded in some areas, typically in voltage and current along with frequency specs, but it must meet the rest of the specs as well, and that includes SOA curves.

You can label a 2N3773 as a 2N3055, and it will comfortably pass any test aside from how the die looks. The other way around it does not work well.

As the devices in question are Motorola and packaged in the cheaper Motorola package, the higher value and military spec Motorola parts would be in a shaped plated KOVAR package with a dome top ultrasonically sealed to the base and with gold plated leads, they do fit the cost of the devices, low cost yet reliable. The remaining old device looks like it was made by Fairchild, who also did offshore assembly of US made dice.
 

Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #329 on: October 11, 2014, 04:06:32 pm »
If you're talking about the parts in my picture, yeah, I had a wide range of choices for the 2N3773s; from 1980's RCA units to modern ST and ON versions. In the end, I went with the mid-90's Motorola parts because the price was right and the seller got me matching date codes (so I could try and get two as closely matched as possible).

The transistors I replaced were also Motorola brand, so it adds a bit of authenticity to the whole thing. =)

One thing I don't understand though... Why did PD specifically use a FS1700E for the driver and MS1700G's for the pass elements? They're both 2N1700's, right? I tested the good MS device and the FS; both have the same curve outputs on my tracer.

Seems weird they wouldn't just use all of one type.


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Online SeanB

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #330 on: October 11, 2014, 05:38:43 pm »
They might be the same device, but different gain binnings. Typically the power devices have a large gain spread, or they were selected for a particular binning for gain within a range at low and high current. with some power devices the gain difference with current can vary from typically 15 at 1A to 0.8 at 40A, and they are still in spec.

e might be binned for good low end gain and the G for good high current capability. In any case the new units will be much better just due to the later tighter process control.
 

Online David Hess

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #331 on: October 11, 2014, 07:06:04 pm »
In the end, I went with the mid-90's Motorola parts because the price was right and the seller got me matching date codes (so I could try and get two as closely matched as possible).

I just buy a few extras and grade them myself.  I recently did this with 2N5886G transistors (80V 25A 200W 4MHz TO-3) and out of four, two matched to within a couple millivolts at the expected operating current.  The original design did not even use emitter ballasting on the parallel transistors so I added that as well when I repaired it.
 

Online SeanB

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #332 on: October 11, 2014, 07:12:41 pm »
A lot of power supplies use equal length emitter wiring to get some matching when running devices at levels where they use 2 or more but want the lower device temp from having more dies and heatsinks. Needs matched devices, preferably to within 5% at operating conditions, but often worked using just devices from the same batch and in the same shipped pack, as they likely did come from the same die and roughly the same area as well.
 

Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #333 on: October 11, 2014, 10:23:50 pm »

In the end, I went with the mid-90's Motorola parts because the price was right and the seller got me matching date codes (so I could try and get two as closely matched as possible).

I just buy a few extras and grade them myself.  I recently did this with 2N5886G transistors (80V 25A 200W 4MHz TO-3) and out of four, two matched to within a couple millivolts at the expected operating current.  The original design did not even use emitter ballasting on the parallel transistors so I added that as well when I repaired it.

That's exactly what I did as well. I needed two, so bought four (with matching date codes to up my odds) and then used my cheap Chinese transistor tester to get the Hfe and base voltages, followed by a run through my homemade curve tracer to verify the current characteristics.

I ended up with two that were about a 1% match. 


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Online David Hess

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #334 on: October 12, 2014, 02:13:13 am »
I just buy a few extras and grade them myself.  I recently did this with 2N5886G transistors (80V 25A 200W 4MHz TO-3) and out of four, two matched to within a couple millivolts at the expected operating current.  The original design did not even use emitter ballasting on the parallel transistors so I added that as well when I repaired it.

That's exactly what I did as well. I needed two, so bought four (with matching date codes to up my odds) and then used my cheap Chinese transistor tester to get the Hfe and base voltages, followed by a run through my homemade curve tracer to verify the current characteristics.

I ended up with two that were about a 1% match. 

A long time ago when I first matched power transistors for parallel operation, I tried a bunch of different methods but found the most cost effective was to tie the base to the collector and measure the forward voltage at a high current but below saturation.  About equally effective was measuring Vbe at the expected base current.  Both correlated well with hfe and produced good current sharing.
 

Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #335 on: October 12, 2014, 07:37:16 am »
Figure this one out... Earlier I was fiddling with the supply I just replaced the transistors on. I was testing out LEDs in place of neon bulbs. As I finished up, I was putting some LEDs back in a box when I saw (and heard) a huge spark emanate from the transistor area on the case! I though maybe a test lead had grounded against the case; everything seemed to still work fine.

A few hours later I was load testing the supply. After I was finished, I turned it off to let everything cool down. About 30 minutes later I come back, flip the switch and CRACK, another huge spark.

WTF? I did a continuity test on all the transistors, the isolation is fine.

There's no scorch marks anywhere and nothing smells.

I've yet to see it happen again, but two times makes me suspicious...


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Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #336 on: October 23, 2014, 12:24:00 am »
So, it's been s bit since my last update on the 2020B! The issue in my last post was caused by a bit of liquid trapped under the Silpad (from the IPA I used to clean the contacts with after soldering).

My parts came in from Digi-Key yesterday, so I put everything in last night.





New banana jacks and neon lamps.







Plus a new fuse holder to replace the one that broke during shipping!

So, I button everything up, plug it in, flip the switch and...problems. =(

If I set it to 1V, I get 1.5xx, with the x being constantly drifting digits. Anything higher than about 3V and it jumps straight up to 28V. The 10-20V range puts the output to 32V. Strangely, even though it seems out of regulation, I can still manipulate the last three digits with the dials (though it drifts up fast).

I have no idea what could possibly be wrong. Last time I checked the unit (3 days ago) it was working fine. I've only replaced what I mentioned above.

Something I did notice, Q4 is getting way too hot; it's at the point of burning your finger if touched. This is the transistor that powers the LM399's heater I think. I checked the voltage across the LM399's Zener pins and I'm getting 7.0028 volts, so that's in spec.

I wonder if Q4 is shorted, or if the heater is shorted even? Hmm.

Thoughts?


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Offline timb

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POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #337 on: October 23, 2014, 11:29:29 pm »
Q4 is fine, so is the LM399's heater.

I started systematically checking voltages last night and finally ran across an issue!

The two inputs of the voltage regulation op-amp are at different voltages. This has to mean that either something in the driver path or feedback loop is broken.

Time to start buzzing out all the wires I think.


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Offline ElektroQuark

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #338 on: October 24, 2014, 07:13:58 am »
Those little beautys are really entertaining.
I really enjoy this type of thread so, I hope you find the fault and plenty of research and photos be needed. I want to see them here  >:D

Offline MarkPalmer

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #339 on: October 24, 2014, 02:50:35 pm »
I love Power Designs power supplies, and use them almost exclusively on my benches short of one HP supply.  I don't have one of the precision models (yet) but have several of the lower voltage/higher current and dual supplies along with one of their 10 V to 6 kV 20 mA high voltage supplies made at Power Designs Pacific in California, who made up to several hundred kV, several hundred pound monsters!   Although decidedly old-school, PD supplies are built like concrete and can take just about anything you could ever dish out to them.  The New York based company lasted in to the 1980's then just sort of dropped off the face of the planet one day, probably bought out by someone.   :(

-Mark-

I'll take apart and post some pictures of the 6 kV supply and post them soon.  You thought this little precision model was interesting.......  ;)


« Last Edit: October 24, 2014, 03:01:18 pm by MarkPalmer »
 

Offline timb

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POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #340 on: October 24, 2014, 03:12:15 pm »
So all the board to control wires seem fine. I started checking diodes (in-circuit) and found two that appear to be shorted. Hmmmm...




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Online SeanB

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #341 on: October 24, 2014, 11:38:35 pm »
Those will read as shorted as they have jumpers across them at the back panel. Those protect the sense inputs.
 

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #342 on: October 25, 2014, 02:53:51 am »
Those will read as shorted as they have jumpers across them at the back panel. Those protect the sense inputs.

I’ve got those removed for testing, as I thought about that. It may be a bad cap after some more testing. But that wouldn’t cause the problems I’m seeing I don’t think. I wonder if it could be the Op-Amp? Hmmm, looks like the OP-05CP is equivalent to the uA741. Might grab one and see.
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Offline motocoder

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #343 on: October 25, 2014, 07:10:30 am »
Those will read as shorted as they have jumpers across them at the back panel. Those protect the sense inputs.

I’ve got those removed for testing, as I thought about that. It may be a bad cap after some more testing. But that wouldn’t cause the problems I’m seeing I don’t think. I wonder if it could be the Op-Amp? Hmmm, looks like the OP-05CP is equivalent to the uA741. Might grab one and see.

Did you check Q3?
 

Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #344 on: October 25, 2014, 07:28:17 am »

Those will read as shorted as they have jumpers across them at the back panel. Those protect the sense inputs.

I’ve got those removed for testing, as I thought about that. It may be a bad cap after some more testing. But that wouldn’t cause the problems I’m seeing I don’t think. I wonder if it could be the Op-Amp? Hmmm, looks like the OP-05CP is equivalent to the uA741. Might grab one and see.

Did you check Q3?

It's on my short list. It's not shorted, but it could still be bad. I'll have to take it out to test it, but I need to fix my cheap Chinese component tester first, as it shit the bed the other day. (I may have blown the ATmega after hooking it to a 9000uF cap that wasn't discharged by I clipped it to a blue-yellow wire instead of a yellow-blue wire in something I was testing...)

Weird thing is, the supply semi-works at the 1V setting (I get 1.5V out), but once you pass 2V or so you basically lose regulation and get 28V. On the 10-20V setting you get 32V.

I guess Q3 could be saturating very early or something? I just don't get what could have killed it. It worked fine the other day! It hasn't even been plugged in!

And Sean, you're right, I double checked and I had the RV/RC jumpers removed (when buzzing out some wires) and thought they were the sense jumpers when I looked last night. (The supply is upside down right now, easy 5AM mistake to make I suppose.)


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Offline motocoder

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #345 on: October 25, 2014, 07:33:44 am »

Those will read as shorted as they have jumpers across them at the back panel. Those protect the sense inputs.

I’ve got those removed for testing, as I thought about that. It may be a bad cap after some more testing. But that wouldn’t cause the problems I’m seeing I don’t think. I wonder if it could be the Op-Amp? Hmmm, looks like the OP-05CP is equivalent to the uA741. Might grab one and see.

Did you check Q3?

It's on my short list. It's not shorted, but it could still be bad. I'll have to take it out to test it, but I need to fix my cheap Chinese component tester first, as it shit the bed the other day. (I may have blown the ATmega after hooking it to a 9000uF cap that wasn't discharged by I clipped it to a blue-yellow wire instead of a yellow-blue wire in something I was testing...)

Weird thing is, the supply semi-works at the 1V setting (I get 1.5V out), but once you pass 2V or so you basically lose regulation and get 28V. On the 10-20V setting you get 32V.

I guess Q3 could be saturating very early or something? I just don't get what could have killed it. It worked fine the other day! It hasn't even been plugged in!

And Sean, you're right, I double checked and I had the RV/RC jumpers removed (when buzzing out some wires) and thought they were the sense jumpers when I looked last night. (The supply is upside down right now, easy 5AM mistake to make I suppose.)


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Check those two protection diodes on the op-amp input too.
 

Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #346 on: October 26, 2014, 12:39:48 pm »
Checked em, they seem fine as well.

Okay, so none of this makes any sense to me at all.

When I first turn on the supply, here’s what I’m seeing:

0V Position: 0.4V
1V Position: 1.4V
2V Position: 27.xV
3V Position: 28.xV
4V Position: 29.xV
(Etc.)

Now, if I turn the dial back to 0V, I get 8-9V on the output and Q4 (the LM399H heater transistor) gets hot as shit. If I pull the current set knob and push it back in, the output settles back at 0.4V and Q4 gets cool again.

Now, here’s something interesting for you: If I hook the reference (ground) lead of my scope to the negative terminal of C4 (without even having the probe connected to anything) the voltage goes down by a large margin (1V is 1.03V, 2V is 2.08V, 3V is 3.22V 4V is 4.4V, 5V is 5.6V and at 9V is starts out around 10V then drifts up to 12V after a few seconds).

Here’s a few scope captures from the Voltage Regulation Op-Amp:


Inverting Input, 6V Output Selected


Non-Inverting Input, 6V Output Selected


Output Pin, 6V Output Selected


Non-Inverting Input, 1V Output Selected


Output Pin, 1V Output Selected

I’m stopping for the night as I’m getting tired (and frustrated) and don’t want to miss something or make a mistake.
« Last Edit: October 26, 2014, 12:42:10 pm by timb »
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Offline robrenz

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #347 on: October 26, 2014, 12:52:29 pm »
The readings you listed imply problems in the Voltage setting resistors and swithches. I suggest setting up the PS for external resistance control as a test. This will eliminate possible problems in the resistors and switches in the unit. You need know good resistances to see what the rest of the circuitry is doing.

Offline timb

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #348 on: October 26, 2014, 01:18:44 pm »
One of the first things I tried. 1k ohms gives exactly the same result as if the unit was switched to 1V (1.4V).

The unit worked fine a week ago and I never touched the switches aside from cleaning them with DeoxIT. I've also measured out most of the individual resistors with kelvin clips and they're spot on.

(In the numbers I gave above, I forgot to add 0V is 0.4V. Last time the unit was working, it was 0.000xxxV, so that indicates a problem outside of the switches, right?)


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Offline robrenz

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #349 on: October 26, 2014, 01:41:30 pm »
(In the numbers I gave above, I forgot to add 0V is 0.4V. Last time the unit was working, it was 0.000xxxV, so that indicates a problem outside of the switches, right?)

Sounds like it.


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