wrt cleaning the PCB, would a standard flux remover also work? [image: image.png]
On Wed, Mar 24, 2021 at 8:52 AM Jeffrey Birt <[email protected]> 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 <[email protected]> *On Behalf Of *Brad Grier > *Sent:* Tuesday, March 23, 2021 8:43 PM > *To:* [email protected] > *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 <[email protected]> > 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 <[email protected]> *On Behalf Of *Brad Grier > *Sent:* Monday, March 22, 2021 10:33 PM > *To:* [email protected] > *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 > 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 > > > > >
