HP 3245a, newbie questions - Page 1
Forum section: electronics / general

author: hp3310a
author_rank: Regular Contributor
timestamp: September 17, 2025, 03:25:19 pm
content: I got an HP 3245a which is in a sorrier state than expected, both externally and maybe internally, too. The seller sold it as working but it doesn't work here (as in "no beep at all").I first made sure the line filter works. I then went to figure out if the transformer windings are OK and it turns out the windings for both 240V and 220V are open circuit (240V is the one I need, alternatively 220V). The unit comes from the US and the 120V winding "works" (or rather "has finite resistance").For both 120V and 100V voltage setting the line voltage gets routed to the connector (pictured below) multiple times, for 240V and 220V there's only one pin pair to which line voltage gets routed. I measured the corresponding winding pins to the transformer at the plug.Code:Switch | Pin Pairs | Winding resistances-------------------------------------------------240V | 1/5 | ∞220V | 2/5 | ∞120V | 1/5 3/5 1/4 3/4 | ∞ 11.5Ω 9.2Ω ∞100V | 2/5 2/4 | ∞ 9.2ΩThe secondary winding has a resistance of 0.49Ω (the two rightmost pins on the plug). Pins counted from left to right.The service manual I have doesn't say there are different transformer variants (label with part and mfg part numbers below), so I guess it is broken?

author: hp3310a
author_rank: Regular Contributor
timestamp: September 18, 2025, 08:50:24 am
content: So, nobody ever inspected the transformer?I'm not sure I want to fire up the unit on 120V (using a variable transformer) to see if it works. Does anyone know what the voltage on the secondary winding is supposed to be? I don't have schematics, if someone does I'd be very grateful.

author: IanJ
author_rank: Unknown
timestamp: September 18, 2025, 08:59:32 am
content: CLIP here:http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/3245A-CLIP.pdfIan.

author: hp3310a
author_rank: Regular Contributor
timestamp: September 18, 2025, 10:20:55 am
content: Thanks a lot Ian!So... to see if the rest of the unit works: Would it (for a short test only) be completely reckless to feed say 16V DC from a lab power supply into the secondary winding connector on the power supply board? The test point J15 (relevant portion of schematic below) right after the bridge rectifier says +15V. That plus 2x diode forward voltage from the rectifier should be a little over 16V.As I said, just to see if the transformer is the only problem.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: September 18, 2025, 11:03:33 am
content: Hi,better use 19V, since the 7815 needs 3 Volt Drop-up.

author: hp3310a
author_rank: Regular Contributor
timestamp: September 18, 2025, 04:37:51 pm
content: Most important thing first: The (rest of the) unit works!Since I don't have a power supply with sufficient wattage (or so I thought) that can do 19V I tried my 15V/30A supply. The max it can do is 16.2V and at 16V the 3245a started working (below that the unit threw power failure errors).At 16.2V it draws only 1.1A, (just if someone has to do this in the future). Given the 80VA line power rating I assumed the unit draws at least 3-4A.I'm happy it works (well everything after the transformer that is). I'm not happy about the - as it turns out - unobtainium transformer. When I have the variable transformer I will know what kind of voltage a replacement needs to produce. Finding a suitable replacement will be a challenge.If someone has a transformer laying around and wants to extort me, you know how to find me....

author: picburner
author_rank: Frequent Contributor
timestamp: September 18, 2025, 05:27:39 pm
content: In the first post, you measured the transformer as if it had a single primary with multiple taps.In reality, it should be as shown in the attached drawing (and so is the 3458A too).Before assuming the worst (the transformer), check that the voltage changer switches are not making false contacts; it wouldn't be the first time that type of switch has caused problems.

author: hp3310a
author_rank: Regular Contributor
timestamp: September 18, 2025, 05:42:44 pm
content: I measured the transformer windings using the pins of the internal connector plug (see picture in the first post). I didn't measure the windings across the switches. I think the switches do work, I tested those by measuring to which pins line voltage was connected to for each individual setting. So for 240V line voltage is connected to pins 1 and 5 for and these are open circuit on the transformer. I'm not sure I misunderstand what you're trying to tell me.I think the 3458a transformer is a different type, it has got multiple secondary windings (at least that is what Tin says here:https://xdevs.com/fix/hp3458a/#a4pcba). This 3245a transformer only got one secondary winding.

author: picburner
author_rank: Frequent Contributor
timestamp: September 18, 2025, 06:00:58 pm
content: I only talked about the primary windings, never the secondary ones because they are obviously different from the 3458A.My transformer tap numbering, which I've shown in the drawing, comes from the 3245A CLIP.What I wanted to tell you is that the transformer has two separate primaries.

author: IanJ
author_rank: Unknown
timestamp: September 18, 2025, 06:38:32 pm
content: If the 3245A really only has one secondary (I can't remember), then it should be fairly trivial to find a replacement transformer at the right VA rating that will give you 220/240VAC input......maybe even a nice toroidal.Assuming the transformer primaries for 220/240 operation are indeed open circuit......If it were me, I'd remove the transformer and inspect the connections closely. I had a 3457A transformer once that had broken wires right at the terminals on the transformer. Easy fix.Ian.

author: Okertime
author_rank: Contributor
timestamp: September 18, 2025, 07:14:42 pm
content: The line selector switches connect these two primary windings in series for the high input voltages.If you pull off the connector and measure the resistance between "your" pin 5 and 1, you measure between the two primary coils which dont have the series connection (the selector switches would provide a short between "your" pins 3 and 4).To gain confidence in the instrument you could close your instrument and measure the input resistance between the two pins of the input power connector whilethe instrument is switched ON. This also proves the function of the selector switches.On my 3245A i measure:Line selector switch, resistance100 V, 11.8 Ohm120 V, 13.0 Ohm220 V, 22.8 Ohm240 V, 24.6 OHM

author: hp3310a
author_rank: Regular Contributor
timestamp: September 18, 2025, 07:25:01 pm
content: Thanks guys, I finally understand what the problem is (surprise, it's me). I'll do it again tomorrow.Also thanks a lot for the resistance values, that should be very helpful!

author: hp3310a
author_rank: Regular Contributor
timestamp: September 22, 2025, 08:42:45 am
content: So, I don't feel like a complete idiot at all...Quote from: picburner on September 18, 2025, 05:27:39 pmYes, they do! I started measuring the switches (from the connector side), first open circuit between P2(6) and P2(5), switched back and forth a couple of times and suddenly it started conducting when in the 240V position. First badly then increasingly better.For those interested in how the transformer windings are actually connected in the different voltage settings, I made a little drawing based on picburners transformer drawing (which is missing in the CLIP linked above).Quote from: Okertime on September 18, 2025, 07:14:42 pmMy measurements differ a little but on their own are consistent:100 V, 6.68 Ohm120 V, 6.79 Ohm220 V, 21.71 Ohm240 V, 23.35 OHMMaybe they didn't always connected the windings in parallel for the low-voltage settings.The individual winding resistances are as follows:P2.4 - P2.6: 11.47 OhmP2.5 - P2.7: 9.15 OhmP2.7 - P2.8: 1.98 OhmSo the switches are good, as is the transformer, the unit powers up. There are a number of other issues but it's a first step.Next will be recaping, any recommendations as to what to use? I have my eye on Nichicon UPJ series for the A6 outguard power supply board and Nichicon UHE series for the A1 inguard source board (all with same voltage and capacitance ratings as the originals).

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 22, 2025, 09:29:25 am
content: I've had adventures with those switches before. The contacts tend to oxidise which causes the issues you saw, especially when switching them after years of never being switched before.I've been known to open them up and physically clean the contacts to get them happy again, but if actuating them back and forth a bunch of times works then that's probably enough.

author: Hydron
author_rank: Super Contributor
timestamp: September 22, 2025, 11:27:28 am
content: Had to change a similar switch in one of my Keithley SMUs once for the same reason. Thankfully though the exact part was still available 30 years after the unit was manufactured, and also was the reason I got the unit cheaply as non-functional.

author: hp3310a
author_rank: Regular Contributor
timestamp: September 26, 2025, 09:09:19 am
content: Since the initial subject didn't really apply, I changed it to something more accurate. I don't want to start a new topic each time my 3245a puzzles me.The fan of my 3245a (Papst 612L, obsolete) was having a bearing meltdown so I replaced it with what I though was the successor EDM-Papst 612 NGLE. To my surprise the new one is much worse, it produces a truly intolerable soundscape and needs to go.These fans from Papst operate up to 15V, which - according to the schematic - is the voltage they get. So they can't be replaced by a 12V fan unless a series resistor is put in to limit the fan voltage (or maybe a different regulator down the road). I tried a Sunon MF60251V1-1000U-A99 (which isn't exactly silent) together with a 47Ω resistor. That gives me about 11.5V at 15V input and the air flow is the same as with the original Papst.I was wondering how others have handled this?

author: eplpwr
author_rank: Regular Contributor
timestamp: September 26, 2025, 04:12:31 pm
content: When the 3245A was a current product, it used the same components as 3458A where possible/applicable, like the fan. The current fan for the 3458A seems to be the Papst 622L model, see the picture at:https://www.keysight.com/us/en/ecom/parts/part-detail.html/03458-68501I am using a Noctua NF-A6x25 FLX with a series resistor to get sligthly over 12V. It is very silent, but the airflow is not as good as the original Papst. My reasoning is that I will not use the equipment in such hot environments as the 3245A (and 3458A) is specified for. And I like to be able to think when I'm using my equipment, which the original fans do not allow for.

author: RolandK
author_rank: Regular Contributor
timestamp: September 26, 2025, 04:30:30 pm
content: Or you can replace the bearings of the fan.Replace the shaffner and the 2 small rifa caps in the power supply near the 110 220 V switch. The schaffner will dislike the change to a higher voltage and fart horrible stinking and sticking glue.Check all voltages for ripple. Only replace caps if you find any. I had it on 34401a's that ripple from opened electrolytics killed the yellow tants.

author: chilternview
author_rank: Frequent Contributor
timestamp: September 26, 2025, 05:56:21 pm
content: Quote from: hp3310a on September 22, 2025, 08:42:45 amYes - don't, unless you know a capacitor is faulty. You can do more damage than good. If you insist, do it one at a time, testing after each.

author: aronake
author_rank: Frequent Contributor
timestamp: September 27, 2025, 03:08:30 am
content: Quote from: chilternview on September 26, 2025, 05:56:21 pmI am not too sure about that recommendation. If never recaped and still have intage late 1980ies, early 1990ies caps, I would definitely swap all of them. I have recaped 6 or so 3458a and its a pretty easy job, at least with a good desolder gun. Also difficult to know what caps are actually good or bad, and there may be some that have started to leak, but not possible to see if not removed.My standard choice of capacitors for electronic measurement recaping are Nichicon 105C caps. In order of preference depending on availability UPW then UPA then UPM then UPX then UTT.

author: chilternview
author_rank: Frequent Contributor
timestamp: September 27, 2025, 07:07:42 am
content: Quote from: aronake on September 27, 2025, 03:08:30 amThe old adage 'if it ain't broke, don't fix it' comes to mind. I've a HP3245A and two HP3458A's and neither have had unnecessary 'fixes' made to them and they perform to spec, why risk breaking them?While those with experience of desoldering may do a good job, it's possible to lift or break tracks if you've not had enough practise or the right tools. But it's your bit of kit to do what you want with...

author: hp3310a
author_rank: Regular Contributor
timestamp: September 27, 2025, 09:22:10 am
content: Thanks for all the good recommendations!Quote from: RolandK on September 26, 2025, 04:30:30 pmReplacing the bearing would be an option if I find nothing else that's adequate. The IEC filter is going to be replaced, it's already waiting on my bench.Quote from: eplpwr on September 26, 2025, 04:12:31 pmYes, agreed, the original fans in those units can drive you insane quickly. The 622L is a whopping €50, so I'll probably stick with a Sunon for now, though the one I mentioned above is still producing way too much noise, I will try with lower RPM versions until it is tolerable.After a Noctua (NF A6x25) terminated itself in my 6611C after only one hour of work, I'm not trusting them any longer. Also, the air flow with those is not nearly sufficient. I recently read a comment by @Kleinstein arguing good air flow is necessary for precision operation in the 3458a (and maybe the 3245a?). So I'm trying not to limit it too much.Can't find the post right now, but it was here not too long ago.Edit:It was here:https://www.eevblog.com/forum/metrology/drifting-3458a-fixed-or-coincidence/msg6047883/#msg6047883Quote from: aronake on September 27, 2025, 03:08:30 amI'm going to recap all caps of one board in one session, there's way to much potential for breaking things doing it one cap at a time. Unplug, unmount, desolder, clean, solder, clean, remount, replug, if you do that 6 times in a row it is a guarantee for disaster. Plus you often can't see damage/leakage until after you've taken the cap off, so they all will get replaced.Quote from: aronake on September 27, 2025, 03:08:30 amThanks for the cap type suggestions, I ended up buying Nichicon UPJ and UHE, but recapping is still on the list, so it's not too late to swap them if you think those are not a good choice. What is the reasoning behind the model ranking, specific properties of the caps or price? I looked at the Nichicon Aluminium Capacitor Type Chart athttps://www.nichicon.com/getmedia/203137de-0c57-457e-b5b4-c848a9d8930f/e-chart.pdf(page 3) for guidance.Thanks again!

author: aronake
author_rank: Frequent Contributor
timestamp: September 27, 2025, 10:56:19 am
content: Quote from: hp3310a on September 27, 2025, 09:22:10 amThat sounds like a good choice. I have made measurements on quite many different Nichicon capacitors I have seen that often any new capacitor have better measured valued than specifications for the supposed to be better capacitor for that parameter. A particular recent case was to find capacitors with low leakage for a noice meter. It showed out the the low leakage capacitors had among the worst leakage !? And all much lower than spec. I would think there often are some differences in production, but part of the reason for so many different types suspected to be related to marketing. Different physical size for same voltage and capacitance obviously are different.