Agilent 66332A Dynamic DC Source 20V/5A Repair and mods

[Macbeth]

Yes, the 6632B does sink current very nicely. You can even set the max current unlike some other Agilent supplies.

It's a 2 quadrant supply, but isn't there a simple board upgrade that is documented in the schematics using relays to turn it into a sorta 4 quadrant? Like a super cheap SMU?

[TheSteve]

There is option 760 which is a polarity reversal relay.

[artag]

There's also app note 5990-3949 http://www.keysight.com/main/redirector.jspx?action=ref&cname=EDITORIAL&ckey=1703016&lc=eng&cc=GB&nfr=-35712.384349.00 which describes using two power supplies for 4-quadrant operation. It's a  bit crude : it just uses them like an H-bridge, so to get full range you have to ensure the supplies are set to opposing voltages. But it does cross zero without a relay glitch.

[Berni]

Yeah there is a connector inside where a little board with a relay fits that simply swaps the terminals around. I thought about DIYing it to upgrade mine but never bothered.

There's also app note 5990-3949 http://www.keysight.com/main/redirector.jspx?action=ref&cname=EDITORIAL&ckey=1703016&lc=eng&cc=GB&nfr=-35712.384349.00 which describes using two power supplies for 4-quadrant operation. It's a  bit crude : it just uses them like an H-bridge, so to get full range you have to ensure the supplies are set to opposing voltages. But it does cross zero without a relay glitch.

Now that's a nice trick i didn't know about. Dang it i only have one unit tho!

[dxl]

Did anyone ever tried to upgrade the Firmware from 6632B to 66332A?

[AndyC_772]

I don't think it's actually a firmware upgrade as such, just a configuration setting.

Isn't there an extra board in the 66332A that does the dynamic signal capture?

[eliocor]

What firmware memory chip (EPROM) is mounted on 66332A?
I can try to replace the one mounted on my 6632B with a new one with the 66332A firmware but I'd like to know what exact chip is used.

[PTR_1275]

I have a 66332a with option 760 (polarity reversal relay) and a 6632b. The 6632b arrived with a smashed screen that I've bought the parts to repair but in between changing jobs and moving house that's not been anywhere near a priority.

When I get some time I'll get the screen fixed and see if changing the option in the menu unlocks it to a 66332a. I'll out of curiosity also check if the 66332a reduces functionality if I set it as a 6632b.

I don't recall seeing any extra boards or component types for the dynamic measurements.

[ElektroQuark]

I have a 6611C, what is it missing from the rest of the family?

[Narmaraktuk]

Many thanks for taking the time to put this up Berni. My 6632B also had a shorted tantalum on the control board, mine was only nearer to the board edge (so say one up in your picture). Seeing someone else with similar issues made for a short repair 

[dxl]

Checked with my HP 6632B but i'm not able to select the HP 66332A type with the calibration setting. Maybe i find some time during the next day to see what firmware it has.

[gslick]

I have dumped firmware version A.01.03 from my 66332A.

I'll have to check and see what firmware version I have in my 6632B.

I have't tried putting the 66332A firmware in the 6632B yet.

[mtdoc]

Many thanks for taking the time to put this up Berni. My 6632B also had a shorted tantalum on the control board, mine was only nearer to the board edge (so say one up in your picture). Seeing someone else with similar issues made for a short repair 

You might want to have a look at Dr. Frank's discovery re: a small design/manufacturing goof on these supplies as spelled out in this thread. I recently picked up a 6632b but have not gotten around to the fix yet. I also have a 6632a. They're excellent PSUs. The current sinking feature is a bonus!

[mark03]

I recently acquired six (!) of these supplies (and one 6632B) at auction.  All but one were wired for 240V.  After I figured this out and changed the transformer connections per the service manual, they are mostly working.  A couple have broken displays, and a few have wobbly knobs.  My first PCB inspections did not reveal any failed capacitors.  I haven't performed Dr. Frank's fix yet.

Here's the strange thing:  Measured on a scope, all of the supplies have ~ 3 Vp-p ripple at 115 to 125 kHz on the output.  Every single one!!  This screams "operator error" to me, but I cannot figure out what could be causing it.  Any ideas?

[carl_lab]

Here's the strange thing:  Measured on a scope, all of the supplies have ~ 3 Vp-p ripple at 115 to 125 kHz on the output.  Every single one!!  This screams "operator error" to me, but I cannot figure out what could be causing it.  Any ideas?

Open sense connections?
Dead output electrolytic caps?

[mark03]

Open sense connections?
Dead output electrolytic caps?

Sense connections are in place.  All of the rail and bias voltages in Table 3-3 check out.  There are a bunch of signal voltages on J307 (between the A2 digital and A1 power boards) that I still need to verify, once I can figure out how to probe them safely.

I think the problem is somewhere in the CV control loop.  When the supply enters CC mode the oscillation vanishes and the output looks good.

I still can't understand how all six of these supplies would have the exact same [previously unreported here] failure, unless they were all abused in precisely the same way.  These came from the Megown T&M auction a few months back.

[Berni]

Perhaps show us some scope screenshots and describe how you measured it.

Oh and does the fast/slow switch on the back do anything? Its supposed to be used to keep it stable with long cables on slow.

[Dr. Frank]

Sense connections are in place.  All of the rail and bias voltages in Table 3-3 check out.  There are a bunch of signal voltages on J307 (between the A2 digital and A1 power boards) that I still need to verify, once I can figure out how to probe them safely.

I think the problem is somewhere in the CV control loop.  When the supply enters CC mode the oscillation vanishes and the output looks good.

I still can't understand how all six of these supplies would have the exact same [previously unreported here] failure, unless they were all abused in precisely the same way.  These came from the Megown T&M auction a few months back.

As they probably come from the same batch or company, they might all have been set up or specially modified for that '332 dynamic thingy stuff.
Maybe you search through all their settings first. As far as I remember, the 6632B has some capacitors parallel to the output, which might be removed in the 332A (just speculating).. what about applying an external cap?

Or do they have jacks on the front?


Btw.: this tantalum cap error is present in the 6632B only, afaik.

Frank

[mark03]

Perhaps show us some scope screenshots and describe how you measured it.

Sure (see attachment).  This was measured with an ordinary 10x scope probe between positive and negative outputs.  Note that the average voltage is exactly correct (4.0V), open circuit or under a modest load (50 ohms).  But if the current limit is tripped, the oscillation goes away and the output is perfect.

Oh and does the fast/slow switch on the back do anything? Its supposed to be used to keep it stable with long cables on slow.

Funny you should mention that!  On all six of my units, there is no switch, only a hole in the chassis covered with a silver sticker, and wire jumpers to fix the unit in the "normal" (slow) position.  The stickers are colored and sized perfectly; it appears to be a professional job, or perhaps manufactured that way?  In any case, per the user manual p. 27 ("Fast/Normal Operation"), this setting should have no effect for open circuit or resistive loads.  The only issue would be if capacitance were added in the "fast" mode.

I checked the voltages on J307 (connector between the analog and digital boards), and thought I'd found a smoking gun when OV_SCR, the crowbar control, was 0.64V instead of the stipulated 5.0V.  A check of the schematic, however, reveals that OV_SCR can never be higher than a diode drop above ground.  I keep finding these small mistakes in the HP documentation, which unfortunately has the effect of making me doubt all of my earlier findings 

FWIW, here's a photo of my analog PCB.  There are definitely some variances with the service-manual schematic.  For instance, U313 (in the current monitor amp) is an AD712 instead of an LM358 as shown; its gain is 2 instead of 1 as shown, due to R427 being a 10k resistor instead of a jumper; and the connection to R427 is made with a bodge wire.  And these observations are just from one small area, since the wire caught my attention.  Perhaps I have an early revision of the PCB?

Btw.: this tantalum cap error is present in the 6632B only, afaik.

Actually, on my 66332A the error is still there.  I haven't changed anything yet because the bias voltages are all within spec, but if I did, what type of capacitor would you recommend?  The SiBaTit ones you used are no longer available.

[Kleinstein]

Instead of SiBaTit caps one can use normal MLCCs, just keep in mind the capacitance reduction with applied high DC bias for some types.  The SiBaTit caps were just an early brand name of relatively high capacitance ceramic caps. Now they go as as X5R and similar.

The AC signal looks a lot like oscillation.  A bad output capacitor (could be just too much ESR) could be a cause. So adding another low ESR cap to the output is definitely worth a try. Even if it does not stop the oscillation it would be interesting so see if the frequency is changing.

Changing the current monitor should not change much in CV mode.

The missing fast/slow switch might indicate the compensation is not as normal - the capacitor (and maybe resistor) values determine if it is slow, fast or something prone to oscillation.

[nctnico]

Perhaps these are special order units tuned for a very specific load. I'd try a large capacitor at the output to see if the oscillation stops.

[AndyC_772]

I might also suggest taking a look at the voltage control feedback loop, and comparing the values of the parts actually fitted against the schematic. Perhaps also remove the main board, take a look at the solder side, and check to see if any parts have obviously been replaced since the board came off the production line.

If the units were a special order, there's a 99% chance that they started out life as tested, working, standard products, which were then changed by hand.

If the fast/slow switches are missing, then your units have definitely been intentionally modified. Also, that modification specifically relates to the transient response in some way, which points a smoking gun at the control loop, IMHO.

[mark03]

Thanks for the suggestions.  I had time to look at this again today, and indeed, a 470 uF capacitor across the output stops the oscillation.  Not being an analog guy, I am hazy on loop compensation.  Could someone explain why adding capacitance would push the output into stability?  For voltage feedback, I thought capacitive loads generally reduced stability.

AndyC's suggestion to look at the PCB solder side was a good one.  I was able to catalog all of the modifications, and it's quite a list, although more components were deleted than anything else.  I picked a good unit to examine, too, because comparing the A1 board from another of my supplies with this first one, there were a couple of differences:  First, the other board looked newer (same PCB rev A3 however), and second, the deleted components were not snipped off like on the first unit; they were never soldered in to begin with.  Definitely a factory modification.

At this point I should probably skip ahead to what I think is the answer.  I should have noticed the white "J02" stickers on the back of my supplies.  This appears to denote a custom option.  I could find no mention of it for the 66332A, but Helmut-Singer has an old document on their web site for the 66312A (a very similar supply):  http://helmut-singer.de/pdf/hp66312a.pdf  See pages 6-10.  The listed component changes don't seem to bear any relation with what I found through reverse engineering, but perhaps the reference designators are different between these supplies?  Here are some choice quotes:

Option J02 is a factory-installed modification which modifies the bandwidth of the 66312A.  [It] incorporates changes to substantially increase the power supply bandwidth and output voltage slew rate. This allows the modified instrument to effectively compensate in remote sense mode for load line voltage drop resulting from very high slew rate load current transitions and thus maintain the remotely sensed output voltage constant. For 0.05 to 0.2 A/usec slew rate loading the transient voltage is reduced an order of magnitude over a standard instrument. There is a  consequence to bandwidth performance improvement. The penalty for higherspeed performance is that stability can no longer be maintained for the wide variety of loads that a standard unit is able to tolerate.

External compensation components:

A minimum load capacitance and series resistance must be maintained for stability. As the remote load may not have sufficient load capacitance, a 25 uF capacitor and 0.25 ohm resistor are fumished, kitted with option #J02. The capacitor is a film type; its low leakage characteristics will not interfere with the uA measurement capabilities of the power supply. The low value of the capacitor results in quick settling time so as to not interfere with the dynamic and pulse measurement capabilities of the power supply. These components are to be mounted at the remote voltage sense points. The remote voltage sense points should be as close as practical to the remote load to minimize additional drop beyond the sense points.

Capacitor Specifications:  HP P/N 0160-8387, Metallized Polyester, 25 uF
Resistor Specifications:    HP P/N 0699-4707, Power Wire Wound Inductive, 0.25 ohm, +/- 5%, 3W

(why an inductive series resistor, and why so hefty?)

Range of Load Impedance tor Stable Operation:

The load impedance can be represented as a capacitance with series resistance (ESR) in parallel with a resistance or constant current sink (the load power-consuming element). The capacitance and ESR can be internal to the load, external to the load, or a combination of both.

* Acceptable range of Load capacitance: 0 to 400 uF.
* Acceptable range of capacitor ESR: 0.2 to 0.4 ohms.
* Acceptable range of Load reactance: Resistive/constant current to capacitive (not optimized for inductive loads).

I was intending to add front binding posts and use a couple of these as bench power supplies.  It sounds like I could just add Ccomp and Rcomp internally and be OK, although the supported range of load impedances is considerably narrower than the standard unit.

[Berni]

Well loop stability can become a complex topic when there are lots of components involved. One case where slowing down the output with a capacitor can help when the control loop has some delay added up trough it while the output reacts very quickly. This causes the control loop to ask the output to rise and because it doesn't see it rising yet it keeps asking it to go up, by the time the control loop notices its rising the output has already went significantly above the desired value and once that comes around to the control loop it asks it to go down sharply. So slowing it down gives more time for the slow control loop to react to its changes.

But yeah usually capacitance is what causes instability, but perhaps the control loop here was tuned to expect a certain amount of capacitance. I wouldn't take those load specs in the datasheet too seriously since clearly the modification messed with the control loop tuning, perhaps it can now handle far beyond 400uF.

[mark03]

I wouldn't take those load specs in the datasheet too seriously since clearly the modification messed with the control loop tuning, perhaps it can now handle far beyond 400uF.

No, those specs are for the J02 option.  A stock 66332A allows for a much wider range of load impedances, at least tens of thousands of uF in normal mode, or significant inductive loads in fast mode.  I'm just hoping that mine can tolerate flying leads of reasonable length, with the compensation components installed inside the unit.

I'm also trying to figure out why an electrolytic cap with ESR ~ 250 mohm (matching the spec in the J02 document) wouldn't be just as suitable as the film capacitor / ww resistor series combo.