Need Replacement Caps For My HP3325a - Page 1
Forum section: electronics / projects

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 03, 2013, 05:39:08 am
content: What can I use in place of the original axial caps on the A3 board of an HP3325a. I've linked a service manual below. I need to replace c6 for sure along with c27 but there are a couple of others I wouldn't mind replacing either. Trouble is that the closest matches I've found are about $30 a piece.Check pages 317-319, thanks.http://cp.literature.agilent.com/litweb/pdf/03325-90002.pdf

author: FenderBender
author_rank: Super Contributor
timestamp: January 03, 2013, 06:09:50 am
content: What are their values?

author: SeanB
author_rank: Super Contributor
timestamp: January 03, 2013, 07:08:54 am
content: C6 I would recommend a NPO 10n ceramic, any voltage, but preferably 100V or higher. otherwise a low TC ceramic disk capacitor, preferably a 250V or higher unit. a 10n class Y capacitor will do here if all else fails.C27 any 10n to 100n disk ceramic capacitor with a voltage rating of 100v or more will do, same for C26,17,56,24,19,51 and the other 100n ceramics can be any value from 100n to 470n 100V disc ceramic.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 03, 2013, 07:18:55 am
content: Quote from: FenderBender on January 03, 2013, 06:09:50 am10nFQuote from: SeanB on January 03, 2013, 07:08:54 amI was afraid that I may be going to disk ceramic. Any predictions on how this will affect the signal?

author: SeanB
author_rank: Super Contributor
timestamp: January 03, 2013, 07:30:34 am
content: The others are pretty non critical, just use a disc ceramic in the range suggested. C6 just use a NPO unit, or a high voltage one, it will not have much effect so long as you are using a low TC ceramic. X7R is definitely out, just use big units.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 03, 2013, 07:40:49 am
content: Quote from: SeanB on January 03, 2013, 07:30:34 amThanks for the info, Sean - much appreciated.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 03, 2013, 07:56:00 am
content: Oh this will work much better for c6 (budget-wise anyway).http://www.mouser.com/ProductDetail/Kemet/C440C103J1G5TA/?qs=sGAEpiMZZMsh%252b1woXyUXj85Xnf6gFcr8amPiE5UZMV0%3dEDIT: Thanks again.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 03, 2013, 01:07:10 pm
content: Hi,Non of the capacitors are super critical.These capacitors from Digikey will work just fine:http://www.digikey.ca/product-detail/en/C410C103K5R5TA7200/399-4452-1-ND/818309They are in stock and they are quite cheap.Jay_Diddy_B

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2013, 09:37:02 pm
content: Quote from: StubbornGreek on January 03, 2013, 05:39:08 amWhy are you sure these capacitors need replacing?

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 03, 2013, 10:47:27 pm
content: Quote from: nctnico on January 03, 2013, 09:37:02 pmThe generator passes self test and 'usually' outputs a 1kHz sine wave but when changing the signal to a square wave or changing the frequency at all, introduces artifacts to the output signal. I just started troubleshooting the problem but these caps measure 280Ohms+ when checking ESR so I figured I'd start there and see if the output cleans up at all.

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2013, 11:40:08 pm
content: I'd start by tracking where the distortion gets introduced into the signal path using an oscilloscope. Ceramic caps almost never fail and never fail in groups. There is something else going wrong. Try the fault finding flowcharts from the service manual to pin-point the cause of the problem.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 03, 2013, 11:53:30 pm
content: Quote from: nctnico on January 03, 2013, 11:40:08 pmI intend to sit down and follow the chart (I really love these old service manuals, almost like cheating) I just haven't had the chance. When I took the cover off, I just quickly checked some of the caps early on in the signal (from the oven controlled oscillator forward) and found two that were way out of wack. Your input is really appreciated.

author: w2aew
author_rank: Super Contributor
timestamp: January 04, 2013, 01:53:32 am
content: Quote from: StubbornGreek on January 03, 2013, 10:47:27 pmThese non electrolytic caps RARELY if ever develop high ESR as a failure mode. This is a usual symptom of electrolytics caps whose dielectric dries out. Plus, ESR meters generally don't operate with a high enough frequency to accurately characterize the ESR of the lower value caps, so your 280 ohm result is probably not correct. I think you need to begin looking elsewhere.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 04, 2013, 02:39:00 am
content: Fair enough and the advice is appreciated. I'll sit down with the service manual (hopefully tomorrow afternoon) and work it out. I'll let you guys know what I come up with - thanks again.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 06, 2013, 03:40:22 am
content: Well, Murphy and his law had their way with me last night. First, the noise in the signal was being introduced by my Owon oscilloscope (its stopped doing that for now but, well, that's a completely different issue) and not the 3325a - once I hooked it up to an analogue Tek scope, all was wonderful. The 3325a really puts out a nice clean signal, especially compared to my Rigol DG1022. If it wasn't for features like arb and duty cycle (umm, important stuff actually which make it a good tool - not knocking the Rigol here), I can't see powering on the DG1022, ever.I played with the HP for a few hours and as I was starting to think the issue was all due to my scope, and shut down the lab, the display went blank on the 3325a and the signal disappeared. Ok, so I powered it off and back on again and all is good. I run the self-test and it passes (this accounts for about 60% of the circuit being in good working order). I proceed to try and duplicate the error for another hour with no success. Why did I shut it down and restart it to begin with?! I should have used the opportunity to find the fault...I have to say that intermittent problems are the most frustrating. I would rather work on something that is dead to the world completely (I suppose that anyone would) than with intermittent issues.I'll keep you guys posted.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 08, 2013, 08:28:15 pm
content: I've been playing with the device for the last couple of days and the generator hasn't faulted (again) yet. I know that as soon as I put the covers on and stack other gear on top it'll laugh right in my face and error out again but I think that this is what I'll have to do for now. Hopefully (not really but) the problem will become a bit more consistent and I'll take her apart again but for now, she's going into action.