Cleaning a Datron 4000

[meandeev]

I need some advice from the community regarding the cleaning (or not) of a Datron 4000 calibrator.

I bought a Datron 4000 from ebay. The device seems rather clean from the outside and the calibrator stickers from 2016 were intact.
A raw check of the outputs with a brymen869 multimeter didn´t show abnormalities.

Because of a fading diplay I decided to open it.
I couldn´t believe, what I saw: The device was very dirty/dusty inside!

The most dust resides on the backside (power supply, heatsink, fan), but also on the power-amplifier (see picture).
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The middle pcb´s were not so dirty, but one can see also a little bit of this characteristic dirt. On the display pcb is a litte more of this.

The dirt is mostly dust, so I could blow most of it away with compressed air.
But a small amount remained on the components - forming a thin layer of dry but a little bit greasy dirt.

Because I was sceptical, I "measured" the resistance of the surface of one of the big capacitors of the power amplifier, that also showed this layer of dirt.
I desoldered it and put 2 test leads with a distance of 1-1.5 cm on it (with some help of a hammer :-) )
Without humidity everything seems ok - but when I breathed on it, I could measure several megaohms.
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If I clean the surface with a dry cotton pad, no resistance can be measured with the same procedure, so it is definitely a problem.

For a first test I started with a not so sensitive pcb, the power supply. I couldn´t remove the dirt layer completely with 99% IPA or "brake cleaner"
(from a car repair shop - my "weapon of mass destruction" for removing grease), even with the help of a brush.
Tap water with some dishwashing liquid worked a litte bit better. But I don´t feel comfortable with water and sensitive electronics...
And the main/chassis pcb is too big to put it in the oven for faster drying without complete disassembling.

So whats your suggestion for the other much more sensitive pcb´s ?

[coromonadalix]

Compressed air  with controlled pressure would do a good job ?  sure the dry pads will help on the bigger surfaces ... cotton swabs ...   paint brush ??

I would not wet the sensitive board(s)  .... until really need to do it   .... and have a good dry time

After a good cleanup,    check for the tantalums and capacitors ...  you have threads here  and some schematics on ko4bb website

[garrettm]

That sounds like some pretty nasty dust!

To be honest, I'm surprised that IPA didn't work. I've had excellent results with using it on all sorts of greasy, gritty, dirty equipment.

You could try using Flux-Off or methanol--possibly both? If you try methanol, you would want to do it outside in a well ventilated area, as methanol metabolizes into formaldehyde and formic acid in the human body.

The sensitive PCBs with high impedance nodes can be cleaned using a commercial can of compressed air (no oil or water content) or compressed nitrogen. High purity IPA or methanol is also fine to use on these boards. You don't want to use a normal air compressor since they will contaminate the boards with micro droplets of oil.

[coromonadalix]

Ipa and break cleaner did not remove some gunk ??   wow  thats nasty for sure


+1  for    @garrettm  comments,  i should have written   compressed air can


But i had some problems in rf boards with break cleaners, some of them did leave some residues ...  some chemtronics brand  pcb cleaners too ...


Now i use  some aqueous pcb cleaners at my shop,  and with hot and demineralized water    i does a great job.     Not sure for non sealed relays ...

[meandeev]

because of your hints and my experience with the power-supply board I cleaned the power-amplifier today (used compressed air some days before to blow away the dust):
- desoldered the 3 relays, the trimmer and the switch on the board (all not sealed)
- gave it a bath of 99% IPA for 30min (pcb completely submerged in IPA) , used a brush
after that some residue left on the board (I knew it from the power supply-board ...) and so I was brave (or stupid) enough to use
- a bath of demineralized water with a drop of dishwashing liquid, also brushed it some time
- a LOT of demin. water to wash the detergent away
- then an additional bath of new IPA for 1 hour to remove the water a little bit and cleaned it again
- used compressed air to blow away the IPA
after this procedure the board looks very clean
- now it´s in the oven at 70°C for drying (if  water exists somewhere )

so it seems that at least some of the dirt is only removable with water based cleaning procedures :-(

[coromonadalix]

ive seen dirt acumulation causing some problems like  humidity and moisture ...  was turning like a gunk