Need help finding replacement SMD caps for HP 16534A Oscilloscope module. - Page 1
Forum section: electronics / testgear

author: Spork Schivago
author_rank: Frequent Contributor
timestamp: January 13, 2016, 10:48:06 pm
content: Hello folks!I bought a HP 16534A oscilloscope module for my HP 16702B logic analyzer. I knew the triggering was broken before I got it and I wanted to try and fix it. I believe I've discovered the problem.On the top side of the board, there's three heat sinks. The middle one says U509. If you flip the board over and find where U509 would be, you'll see a little circuit with some SMD caps and SMD resistors. I'm missing two SMD caps. I've circled the two that I'm missing.I was hoping someone might know what size / voltage caps I would need and if not, maybe someone had the same HP 16534A oscilloscope module and they could just look in that area, find the two that I'm missing, and take a glance at the other ones in that area, to see if they could find two that are the same size (ie, length / width / height). That way, on my unit, I could pull those other two and use my ESR meter to determine the capacitance at least. I'd still need a way to find out what voltage they are.Anyway, here's a picture with the two caps that I'm missing, they have a red square around them. This is a pic from someone elses board. Any help would be greatly appreciated!!!Thank you!!!!!

author: PaulAm
author_rank: Frequent Contributor
timestamp: January 14, 2016, 07:44:16 pm
content: The one on the left is 2.25mm long by1.45mm wide. The one on the right is 2.32mm x 1.43. +/- 01mm About 1mm high. The solder fillets may be messing up the length measurement a bit. Unfortunately, they have no discernible markings.EDIT: the two above the 4 resistors are very close in size.My board actually only has 2 heatsinks. There's a small daughter board instead of a hybrid in the middle position.. My board is marked factory refurbished 7/8/02.Change out the Dallas nvram on the board. I got my board cheap because it failed self test and it was due to a dying NVRAM. Once I replaced that it passed self test and auto cal. It's been a while, but it might have been the triggering that was at fault.

author: Spork Schivago
author_rank: Frequent Contributor
timestamp: January 14, 2016, 11:01:02 pm
content: Quote from: PaulAm on January 14, 2016, 07:44:16 pmThanks for your help! I wonder if I should check the capacitance out of circuit for those two that are around the same size or remove them first. Because I don't have the two missing ones, my logic was other caps in that circuit that were the same size would also be the same capacitor. I know it's not the best idea, but I don't really have any other thing to go on at this point in time.For my board, I also have a daughter board, but it's a little bit further back than the U509 that I was talking about.Where's the NVRAM located on the board and what should I replace it with? Doesn't NVRAM hold data with no power applied, like settings and stuff? Been a while since I played with that kind of stuff. Would I have o dump anything and transfer it to a new NVRAM chip or do I just unsolder the old and put a new one in? Thanks!

author: Spork Schivago
author_rank: Frequent Contributor
timestamp: January 14, 2016, 11:09:47 pm
content: Dang it all, looks like I gotta pull those two above the resistors to check their capacitance. When I use my ESR meter, they show in-circuit / leaky. One showed an ESR of 1.30 Ohm. Hopefully they're not too hard to pull. The missing ones almost look like they were glued on or something and then soldered in place. Hopefully that red stuff that was under them wasn't glue and they come right off with a hot air rework station or a soldering iron.Maybe if you have an ESR meter, you could just try measuring the capacitance of the two that I'm missing, you know, just to see if it shows a value or not. If not, it's okay. I don't want you to go through a lot of work for me, like removing them and then testing them. If they don't test in circuit, I wouldn't worry about it. I'll start on pulling those two above the resistors and checking their values and looking for some replacements that are similar in capacitance. Hopefully those two are the exact same.Does anyone know how I could determine the voltage for the missing caps?

author: PaulAm
author_rank: Frequent Contributor
timestamp: January 14, 2016, 11:33:30 pm
content: It's the black rectangular package at one of the back corners of the board. Look for U808 by the edge with the cut corner.My mistake, it a ST Microelectronics chip, not a Dallas chip. It's a M48Z18-100PCI. Mouser stocks them for $12.58.It holds the cal values, but they get replaced during the autocal procedure. I just replaced mine and it worked.My LCR meter doesn't come up with anything useful while they're in circuit. Sorry about that.

author: Spork Schivago
author_rank: Frequent Contributor
timestamp: January 14, 2016, 11:53:21 pm
content: Quote from: PaulAm on January 14, 2016, 11:33:30 pmOh cool, you got an LCR meter? Are they better than ESR meters? I was thinking of getting one. I thought maybe they could be used to check coils and stuff. Maybe I'm thinking of a different tester though.Thanks for checking with the meter! I also found that NVRAM part. On mine, it says it has a lithium battery inside. I bet it's dead. Once I get those caps replaced, I'll work on replacing that NVRAM! Thanks for all the help!!

author: Spork Schivago
author_rank: Frequent Contributor
timestamp: January 15, 2016, 01:10:25 am
content: I pulled those two caps. One measures 10.04nF, the other 10.21nF. Would it be safe to assume they're 10nF SMD caps? Any idea what voltage they might be? Thanks!

author: Spork Schivago
author_rank: Frequent Contributor
timestamp: January 15, 2016, 01:27:14 am
content: I'm thinking the package size might be 0805. That seems to be the closest size to all the available sizes.