Agilent 54622D - Cleaning the dirt out.

[Robomeds]

So I've gone on a bit of a scope bender recently and picked up two in the last two months, both Agilent 5642x family.  The first is a 54621A in great shape other than needing a new battery.  It's very clean on the inside.

The second is the mixed signal version, 54622D.  It was sold as not powering up.  Thanks to having two scopes it's easy enough to swap the power supplies for testing purposes.  With the swapped supply the scope powers up and largely works but failed the user cal test.  The specific error is "Mutli Channel Path Delay, failed".  Of note is the scope is quite dirty with what feels like it might be a bit of a waxy or oily dirt/dust.  Simple compressed air didn't seem to clean it that well. 

At this point I suspect both the power supply and cal failure may be related to the dirt inside the unit (hunch/guess).  So this brings up three questions.

1.  What is the suggested method for cleaning these boards?  I've seen people suggest alcohol (seems they are normally thinking about cleaning flux) or dish soap and water (is this a good idea with BGA packages on the board).  I've got contact cleaner which I'll use on the buttons and encoders (they need it).

2.  Any suggestions for looking at the power supply?  I do at least have a second near identical supply to test as a point of comparison.  I don't see obvious failures (caps, bad traces etc).  Worst case I can get a supply off ebay.

3.  Any suggestions for a low cost logic analyser cable?  Mine came with none and I don't feel like spending $200 if I don't have to.

Thanks!
Anyway, thanks for the help!

[CJay]

I'm sure I've seen it mentioned here about HP or Tek cleaning boards with de-ionised water and soap followed with a thorough rinse and a bake in a low temperature oven (something specially designed for the purpose no doubt)

I, personally, have cleaned boards that way too, as well as in the dishwasher, in some cases they were better than factory but you have to be extremely careful the water can't get into anything and it absolutely has to be washed down thoroughly and completely dry before powering on of course.

I'd be worried about water in switches, controls, anything mains or high voltage and in anything socketed.

[EHT]

I have a 54622D as well. It is a great scope, so well worth fixing up. I'm very impressed with the "mega zoom" on the delayed timebase, the ease of use and responsiveness. It is also really well built.

I wouldn't recommend using water on any parts other than the case, knobs etc. For the PCB, clean carefully with cotton buds and IPA. Still, I doubt this is causing the error.

Could it be possible that the 2 PSUs are not quite the same spec, or missing some extra supply line(s) on the 54622D over the 54621A? The former must have more logic devices in it. Howabout you focus on fixing the broken 54622D PSU rather than cleaning the main PCB?

There is a guy on eBay selling home-made logic leads for these. He has taken leads from an Agilent LA and then made a small PCB to slot into the edge connector on the 54622. They aren't cheap, but much cheaper than trying to get an original set.

BTW, does anyone have info on changing the battery in the 54622D? I did see some chat about it, but it wasn't clear to me if critical calibration settings would be lost if it were removed or not (like older equipment that stores setting in SRAM like HP3457A etc.).

If you do put it in the dishwasher please post pics

[HighVoltage]

I had many Agilent dirty PCB's placed in alcohol and then in addition used a brush to clean the parts.
When you are done, place the board in an oven at 50 °C for a few hours to get all alcohol out.

This procedure has worked every time for me.

 

[Robomeds]

Thanks everyone.  I've been traveling and with various home/family projects I haven't had the chance to pull things apart again. 

Just a few points, I don't think there is any difference between the power supplies.  The layouts are virtually identical (probably not the same supplier or perhaps a board rev etc).  I would like to figure out what is wrong with the bad since that is the primary thing that keeps the 45622 off line.  If the dirt is anything other than non-conductive dirt I could certainly see it having a negative impact on the system's operation.  Anyway, when I get a chance I'll dive in again.

[No.Mad]

Hi Robomeds,

hope you managed to deal with the issue. If not (I know it's almost 2 years but maybe this would be helpful for anyone) my suggestion is:

During my time in PCB manufacturing we used this for military standardised assemblies:

https://uk.farnell.com/electrolube/swas05l/cleanser-aqueous-super-swas-5l/dp/725687?MER=bn_level5_5NP_EngagementRecSingleItem_1

Pour enough solution in glassware placed on ESD surface to soak whole board you want to clean. Let it soak for approx. 10 min, then using brush NOT MADE of synthetic material to gently wipe still submerged board. After 20 min. of wash you can rinse it thoroughly with tap water (lower IPC class) or de-ionised water (IPC Class 3 Military grade, my recommendation). Then procedure tells you to bake it for at least 2 hours in 60 Celsius degree. This should get rid of any dirt you could imagine and electromechanical parts should be fine.

Regarding PSU module: there is whole service manual online: https://www.manualslib.com/manual/642490/Agilent-Technologies-54621a.html?page=110#manual

You could just plug it (watch out for mains!) and measure test points for voltage levels. Dave got a lot of clips on YT like that, just follow the drill

Can't help you with logic analyser cable but maybe you could ask around maker / hackers community? There are a lot of blokes (and ladies of course) that makes various stuff so probably one of them made that cable already and even maybe sells it.

Hope it helps bruv.