On 3/24/21 9:10 AM, Stephen Adolph wrote:
wrt cleaning the PCB, would a standard flux remover also work?
image.png
It's good to have a can or two of that stuff around for the odd
situation, but mostly it's way too expensive to use all the time.
I have found that stuff not to actually work that great. Not any better
than plain alcohol anyway.
With old dried rosin flux, it takes time for the solvent (any solvent,
that special exotic stuff or plain alcohol), to get in and soften the
flux before it washes away. But that stuff evaporates almost instantly
so it spends no time at all in contact and working on the flux. So you
end up spraying and spraying and just using up entire cans to get nowhere.
And then even when it DOES start to wash away, or when it's fresh flux
that starts dissolving right away, even then, it never really washes all
the way away. There is always a sticky surface left behind when the
solvent dries. Often also a white residue.
That's why you need to do the trick with kim wipes and a paint brush or
cleaning brush, or jersey t-shirt cloth, or even paper towels. You need
the cloth or paper towel to attract and trap the rosin while the solvent
has the rosin dissolved and mobile.
I have wasted entire cans of that aerosol flux wash and still had a
sticky board. Spraying onto the board while the board rests on some
folded up paper towel helps, so the spray run-off carries the dissolved
flux into the towel where it is trapped.
It does dissolve the flux and you can *eventually* get a board clean,
but it's crazy expensive because of how much you burn through. And even
then, it still leaves flux trapped under SMT chips usually.
What REALLY works is a combination of an ultrasonic cleaner and a proper
saponafying cleaning solution.
But a M100 motherboard is large, and you don't want to submerge it
because it has components that wouldn't like it. So this isn't an option
really for that.
But for small boards I have been using this particular ultrasonic cleaner:
https://www.invisiclean.com/invisiclean-pro-elite-ultrasonic-cleaner.html
and Branson EC cleaning solution.
That particular cleaner is good because it has 2 transducers, and
because it's small and doesn't have any heater or sweep frequencies it's
still only $60.
The heater doesn't matter because a microwave is much faster anyway, and
you are dumping out the water before it even cools down.
And the low power (not that many watts of ultrasonic power) I think ends
up being a benefit because it's gentle. It takes longer to get the job
all the way done, but you can buzz a board all day long without hurting
it. Over the last few years as I've been continually tweaking the design
of my rex re-make board and all those other little DIP and credit card
sized boards, I have actually been desoldering and re-soldering all the
components from old boards to new boards, and so the same chips have
been through the ultrasonic many times over by now and they all still work.
And the cleaning solution is special. It's a saponafying solution that
turns the rosin into soap, which is then water soluble.
The heat is a factor too, the heat physically melts the flux so the
ultrasonic and the chemical can actually get at it.
With that cleaner and that solution, I just take a 2-cup glass measuring
cup of distilled water and nuke it for 3 minutes and dump it in. Then
add one capfull of Branson EC, and that simple recipe works out to the
right 150F temperature and 4% concentration. Then hit the timer for it's
highest setting of 600 seconds. It takes a while for flux to start
breaking up and dissolving out from under chips and from inside other
tight places like inside female connector pin holes. But usually bythe
end of a 10 minute run it's all done. I usually stir the boards around a
little with a spudger stick so they get exposed to different "hot spots"
where the sound waves concentrate or resonate. Not sure it really makes
much difference. It might be like watching the pot boil. ;)
But for a big/old/not-submersible board like a 100 mainboard, you're
best bet is 99.9% isopropyl, or "denatured" alcohol from the hardware
store which can be a lot easier to get a-hold of, and some kind of
absorbent sheet like paper towels, or those thick shop towels from the
hardware store or auto parts store, or t-shirt scraps. They even sell
big bags of t-shirt towels at the hardware store. And a medium to stiff
parts cleaning brush or small paint brush. Soak the cloth in alcohol and
poke the brush into the board. Use all kinds of random motions and
directions, a combination of jabbing and poking straight in, and
brushing side to side and circles, and keep moving to fresh areas of
cloth as it gets loaded up.
For small boards sometimes I use Kim wipes because they leave no lint
behind. But they are tissue thin and don't absorb very much before you
need a fresh one. But they do trap the rosin well and leave behind a
nice clean board. They are good for cleaning up an individual spot like
one footprint during re-work or repairs.
--
bkw
On Wed, Mar 24, 2021 at 8:52 AM Jeffrey Birt <bir...@soigeneris.com
<mailto:bir...@soigeneris.com>> wrote:
I was also reminded this morning, by another email, of the evils of
the flux used on the M100. It can turn conductive and cause
everything from the machine being stuck in reset, to power supply
issues to fantom key presses. It is also a pain to clean off. I like
to add about 10% glycerin to 90% alcohol (99% alcohol), paint it on
the back of the PCB, wait 10 minutes and scrub it with a toothbrush,
flush with alcohol and repeat. If you only have alcohol that will
work too. I think the glycerin helps as it increases the viscosity
enough to keep the alcohol in place.____
__ __
Jeff Birt____
__ __
*From:* M100 <m100-boun...@lists.bitchin100.com
<mailto:m100-boun...@lists.bitchin100.com>> *On Behalf Of *Brad Grier
*Sent:* Tuesday, March 23, 2021 8:43 PM
*To:* m...@bitchin100.com <mailto:m...@bitchin100.com>
*Subject:* Re: [M100] In over my head? Or a Challenge!!____
__ __
Thanks Jeff! I just watched that video and it was *very* helpful. I
may have gotten ahead of myself in the diagnosis so looking forward
to putting some of your techniques to use. I'm thinking I can do
most basic testing with my multimeter, but should probably look at
getting a proper o-scope in the near future. Tempted by those cheap
ones but they don't go into the 2mhz range :(____
__ __
Thanks again for your advice -- it's appreciated.____
__ __
--Brad____
__ __
On Tue, Mar 23, 2021 at 8:00 AM Jeffrey Birt <bir...@soigeneris.com
<mailto:bir...@soigeneris.com>> wrote:____
I did a video a while back about the first steps in
troubleshooting a vintage computer. In a nutshell think ‘PCR’
Power, Clock, Reset. Make sure that all power supply rails are
functional, then check that you have a good clock signal and
finally check for a properly working reset. Without these 3
basic things nothing else will work and you can get confusing
results. For example a reset that does not work properly can
cause everything from not booting at all (held in reset) to the
system coming up various random states as things were not
properly reset.
Jeff Birt____
____
*From:* M100 <m100-boun...@lists.bitchin100.com
<mailto:m100-boun...@lists.bitchin100.com>> *On Behalf Of *Brad
Grier
*Sent:* Monday, March 22, 2021 10:33 PM
*To:* m100@lists.bitchin100.com <mailto:m100@lists.bitchin100.com>
*Subject:* [M100] In over my head? Or a Challenge!!____
____
Hi everyone, as the subject line says, am I in over my head (for
someone with old basic electronics knowledge), or is this a
worthy challenge?
[TL;DR] System symptoms: Won't power the screen, BASIC doesn't
really work, unusual voltages on LCD connector pins. What to do?
And why??____
____
A few months ago I received a M100 that wasn't really working.
Initial symptom is no display. I was looking at this as a
learning experience -- to see if I could do some simple fixes
and get it going again, and dust off my ancient basic
electronics knowledge. I only have a multimeter, so I knew this
could be a challenge.____
____
Initial testing revealed that it did power up and will 'Beep' on
command (blindly entering Basic and typing Beep<enter>). ____
____
LCD does work -- I connected it to my NEC PC-8201a and had a
functioning display (with a tiny line of dead pixels in zone 1).
So I'm ruling out a bad LCD.____
____
The mainboard looks fine. No obvious scratches or leaking
battery or caps. No obviously damaged components. No staining of
any kind other than the standard-issue coating of flux (which
I've read can turn conductive so I'm open to cleaning all that
off too). ____
____
Display-related transistors and diodes (according to the
troubleshooting flowchart) check out. The caps look great too --
but I haven't desoldered each of them to test them out of
circuit. I've read recommendations to recap anyway, but I'm not
sure it'd be worth it if the other problems aren't related to
bad caps.____
____
Voltages on the LCD Connector pins seemed weird when compared
with my NEC PC8201a. Image here: https://imgur.com/a/xfNIdF1
<https://imgur.com/a/xfNIdF1>
Related to caps? Something else? The LCD is getting these
voltages (the cable is fine).____
____
So now I'm thinking there might be something with the logic. So
I tried typing a simple basic program, blindly, but it's a short
program so I'm pretty sure I got it in properly:
10 beep____
20 goto 10____
____
Nothing. No string of beeps. ____
And after that, a simple beep<enter> won't work either. ____
____
But, power cycle or reset, enter basic, type beep, it works.____
beep:beep:beep also works. Now I'm thinking partially bad RAM?
Or RAM select logic?____
____
So, two issues (display and BASIC), or is this all a case of a
bunch of invisibly bad caps and I should just bite the bullet,
desolder a few and test them.____
____
Thoughts? Ideas? What am I missing? Is this thing destined for a
parts computer or could it be a good challenge to heal it up?
All advice appreciated :)____
____
--Brad____
____
____
____
____
____
____
____
____
____
____
-- ____
--
Brad Grier____
____
____
____
__ __
-- ____
--
Brad Grier____
__ __
__ __
--
bkw
