White "fungus" around a ni-cad

[N_Cook]

What exactly is it and what , if any, damage does it do to anything
adjascent/ same box.
Thurlby DSA524, digital scope adaptor From 1987 . Nickel dendrites like Tin
whiskers ?
Went to use it for the first time in 5 years and no response to any input,
was ok previous use. A vaguely staircase output on an analogue scope , but
thats about all. Composite and trigger out work as do some anunciator
readouts. So presumably ROM, RAM, PS, Clock are ok. So is it realistic to
suspect the A-D a Ferranti ZN449. ? One of those "better than nothing"
service manuals is out there but thats about all
This happens to be right next to one of those pcb soldered oval shape blue
cased nicads of that era, before EEPROMs came in.

 

[N_Cook]

It is potassium hydroxide electrolyte, and it is very corrosive. Put on
rubber gloves, and carefully wash the affected area with water. Follow
up with vinegar to neutralize what's left, and then rinse with water
again.

I once had to clean up an old (really old, it had miniature vacuum tubes
in it) H23BAM police radio with NiCd wet cells. I skipped the rubber
gloves, and despite being careful, I had no finger prints when I was
done. The residue etched the ridges right off.

Doug White

Pineapples remove fingerprints also, but we eat them

I can't see how KHO creates tendrils or matting or whatever the 3D tracery
structure is

 

[N_Cook]

Relevant looking signal (alternate time slices varies with varying DC at ch
1 and ch2)gets to the analogue data-in of the ZN449 , enable, clock etc ok
but invariant data out on the 8 data lines.

I've some SMD ZN449 , any tips for converting to 18 pin conventional DIL?
Start with a turned pin socket in the pcb to receive another one to carry
the SMD, yes but any other tips ?

 

[N_Cook]

Will have to deal with the conductive contamination on the pcb around
the nicad, down to 300K over the polyester of the pcb, soaked in
capilliary-wise?. Removing 4x 74HC as well as the ADC

 

[IanM]

Will have to deal with the conductive contamination on the pcb around
the nicad, down to 300K over the polyester of the pcb, soaked in
capilliary-wise?. Removing 4x 74HC as well as the ADC

Conc. aqueous potassium hydroxide (KOH) attacks E glass
(alumino-borosilicate glass fibre) leaving an insoluble white amorphous
deposit of potassium silicates and aluminium hydroxide. This deposit
will be conductive if contaminated with residual KOH as KOH is both
ionic and hygroscopic and will be extremely difficult to remove as it
has probably etched its way below the board surface. After aggressive
cleaning, neutralisation, thorough washing and oven drying, you will
still probably need to grind away the affected PCB surface until the
track to track resistance remains acceptably high after 24 hours
exposure to normal atmospheric humidity, then wash, re-dry and rebuild
the ground away areas with epoxy.

KOH also attacks a number of common plastics to a greater or lesser
degree. Polyester is likely to be moderately affected, Epoxy is
resistant. If you are very lucky, it may simply have made the resist on
the PCB surface conductive and not attacked the underlying fibreglass
significantly.

 

[N_Cook]

Conc. aqueous potassium hydroxide (KOH) attacks E glass
(alumino-borosilicate glass fibre) leaving an insoluble white amorphous
deposit of potassium silicates and aluminium hydroxide. This deposit
will be conductive if contaminated with residual KOH as KOH is both
ionic and hygroscopic and will be extremely difficult to remove as it
has probably etched its way below the board surface. After aggressive
cleaning, neutralisation, thorough washing and oven drying, you will
still probably need to grind away the affected PCB surface until the
track to track resistance remains acceptably high after 24 hours
exposure to normal atmospheric humidity, then wash, re-dry and rebuild
the ground away areas with epoxy.

KOH also attacks a number of common plastics to a greater or lesser
degree. Polyester is likely to be moderately affected, Epoxy is
resistant. If you are very lucky, it may simply have made the resist on
the PCB surface conductive and not attacked the underlying fibreglass
significantly.

Maybe I'll be lucky. Removed 5 ICs and the nicad from that area. Washed
locally with meths and while still wet dremmel and rotary wire brushed over
that area . Now I cannot find any conduction to/between any isolated pads or
the plastic/glass less than the 30Meg of my DVM. Made good the IC holes
ready to receive 5 turned pin sockets

ps
I also have a > 30K filter on my (valid) email inbox. It is me who decides
who clogs up my inbox /HD

 

[IanM]

Maybe I'll be lucky. Removed 5 ICs and the nicad from that area. Washed
locally with meths and while still wet dremmel and rotary wire brushed over
that area . Now I cannot find any conduction to/between any isolated pads or
the plastic/glass less than the 30Meg of my DVM. Made good the IC holes
ready to receive 5 turned pin sockets

ps
I also have a > 30K filter on my (valid) email inbox. It is me who decides
who clogs up my inbox /HD

Sounds like it was just surface contamination or leaky resist. I would
wet scrub it with deionised water with some IPA as a wetting agent using
a abrasive pencil type glassfibre brush to be certain the dremel wire
brush hasn't left any metal contamination that may give you trouble with
metal salts later, Rinse well with dry alcohol and dry thoroughly
with forced air circulation at an elevated temperature. Finally coat
the damaged area with a good brand of solder-through PCB lacquer before
refitting any components.

If I think there is any chance of future battery leakage I usually fit
the new battery through a piece of polyethylene, silicone or ptfe sheet
between it and the board to limit the damage next time.

 

[N_Cook]

Sounds like it was just surface contamination or leaky resist. I would
wet scrub it with deionised water with some IPA as a wetting agent using
a abrasive pencil type glassfibre brush to be certain the dremel wire
brush hasn't left any metal contamination that may give you trouble with
metal salts later, Rinse well with dry alcohol and dry thoroughly
with forced air circulation at an elevated temperature. Finally coat
the damaged area with a good brand of solder-through PCB lacquer before
refitting any components.

If I think there is any chance of future battery leakage I usually fit
the new battery through a piece of polyethylene, silicone or ptfe sheet
between it and the board to limit the damage next time.

Well I suppose that is progress. Back to exactly the same malfunction as
before , but with the 5 original ICs in sockets now. Varying activity on the
analogue side of the ADC and no variation at any of the 8 output digital
lines . Will try a SM ZN449 , which strangely is wider package than standard
DIL. so looks like it will have to be a skewed adaption to fit .
Using the original nicad at the moment, slung underneath. I like the idea of
a silicone bund. I think , if I get this working, I will replace with a
new one , stout-wired upside down, right side of the board , over a
silicone sweet or cupcake mould

 

[N_Cook]

My tip for a SM IC to DIL adaption.
3/8 inch wooden dowel , cut a small flat to receive the SM IC neatly.
0.2mm tinned copper wire, free end looped around first pin , around the
dowel with a bias so the wire lays tight against the up-side of the opposite
pin and wind biased spiral fashion over the top of the IC and around the
dowel. Finish with a final loop around the last pin. Clamp free end of dowel
in a vice and solder each pin to its wire. With a razor cut the wires over
the top of the IC close to the pins and cut along the centre back of the
dowel. straighten wires. Some 1mm PTFE spaghetti tubing , small length
pushed over every other wire and glued to the IC body. Fan out the wires and
solder to the pins of a turned pin socket. Continuity check for contacts and
bridges.

 

[N_Cook]

Wow, that's a lot of work. Why not just use a footprint adapter, e.g.
the ones from Bellin? http://www.beldynsys.com/

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

I was not aware of them but can they adapt from wide .45 inch SM down to .3
inch DIL for this purpose and 18 pins ? And for one offs,? thats more for
production environment at 40 squid a pop .
My free "adaptors" are fully adaptable to any contingency, just don't look
so pretty, and probably a bit higher profile due to use of a socket.

 

[N_Cook]

I don't think you'd use them in production, because you could lay out
your own and they'd probably be cheaper. The Bellin ones work out to be
under a buck each. They're dead useful for protos and repairs--I have a
couple of sheets of them, about $70 worth, and use them with some
regularity. You do need a couple of rows of pins to connect to the main
board.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Come to think of it, my method would look neater without the intermediary
socket. Larger dowel and longer cut 0.2mm wires, so can pass through the
original board. Just that over the years I've got in the habit of socketting
any replacement IC I've desoldered, there's always been the height available
with the stuff I deal with .