What gets to these AE (aluminum electrolytic) caps is the internal current they see while an A.C. voltage is applied (the ripple voltage). This creates internal heating and "cooks" the moisture out that is in the electrolyte, causing internal pressure. This being caustic, causes damage to the PCB traces when it leaks past the seals. So you have several things going on that kill them:
- Internal heating - Which is a function of the capacitors ESR (equivalent series resistance/reactance) and the frequency and potential of the A.C. (alternating current) it is being asked to absorb. - External heating - This being applied by other nearby components, and the ambient temperature. - Component aging - How old is it relating to the effectiveness of the seals (rubber end seal in the case of the capacitors used being radial mounting types). And has the electrolyte all dried out causing the capacitor to potentially short out. As Birt pointed out, the AE caps are likely only temprature rated at 85C (the parts list doesn't say) which is O.K. for a consumer device, but generally this rating does not lead to quality parts from every manufacturer, in my experience. As far as the Model 100 is concerned, it has been my experience that C82 seems to be the first one that gives out. As seen on the schematic, it is filtering the raw 6V power nearest to the switching transistor and is snubbing the back EMF from the transformer primary. I am replacing it now in my development M100, where I noticed leakage while replacing the 40pin System Bus socket with a ZIF (Zero Insertion Force) socket and replacing the memory NiCd battery. >>>Josh<<<; What do you find is the best way to neutralize the damaged area to the PCB? Since you seem to have the most experience with leaky caps here on the list. It does get under the solder mask, so I think I will have to strip the solder mask area first before neutralizing. Regards, Peter <snip> > ------------------------------ > > Message: 5 > Date: Wed, 19 Aug 2020 06:59:11 -0400 > From: Josh Malone <[email protected]> > To: [email protected] > Subject: Re: [M100] Preemptive recapping > Message-ID: > <CAB== > [email protected]> > Content-Type: text/plain; charset="utf-8" > > My current recommendation is to replace C82 through C86 preemptively on all > Model 100s. I've probably seen close to 75% failure rate on one or more of > these caps. The rest I would only recommend replacement where indicated; if > you see actual leakage or if the machine is known to have lived in a hot > and humid climate. The 102 seems far less likely to need recapping, and I > don't yet have enough experience with the 200 to form an opinion. > > That said, console5 is a reputable supplier and if you have the experience > and tools to recap the machine entirely, it probably won't hurt. Most of > the dangers from "shotgun" recapping comes from using poor-quality > replacements or people damaging the machine because they don't know how to > do the replacement properly (improper dwell times, wrong temps, clipping > leads and soldering to existing joints), or use poor tools (unregulated > irons, poor solder suckers). > > -Josh > > On Tue, Aug 18, 2020 at 10:49 PM B 9 <[email protected]> wrote: > > > I came across a site selling a kit of capacitors for the Model 100/102 > > < > https://console5.com/store/tandy-radio-shack-trs80-model-100-102-cap-kit.html > > > > and I was wondering how important people think it is to recap a system > > which is working fine. My general philosophy is, if it ain't broke, don't > > fix it. However, I know for some other archaic computers, the capacitors > > are notorious for not just going bad, but destroying more expensive parts > > when they do. Are the model T's known to do that? > > > > Thanks, > > > > ?b9 > > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.bitchin100.com/private.cgi/m100-bitchin100.com/attachments/20200819/c8dc01e6/attachment-0001.html > > > > <snip>
