[vcf-midatlantic] TRS-80 PC-1 & Printer

[Herb Johnson]

David Gesswein posted:

> I would always recommend opening up and checking anything you know has a
> battery in it. They frequently leak which will damage whatever is nearby.
> Nicads leakage seems to be less volume than some other types.
>
> Powering it up with the leakage would likely make things worse.

There's many kinds of batteries inside vintage electronics; it's useful 
in my opinion to identify what you have. Generally you should not 
replace one kind with another kind. I'll walk through  reasons - do your 
homework before serious work. I won't discuss lead cells or gel-cells.

NI-cd's or Nicads work at different voltages than Nickel-hydride which 
is the more recent alternative. Lithium cells are usually very small 
batteries. Leakage is a problem, among other problems.

Nicads have a longer shelf life, can be completely discharged but still 
are rechargable - good for those solar yard-lights. They usually don't 
leak, but do corrode and produce a flaky material. You can still obtain 
NiCd batteries, for equipment which may sit for months and then be put 
back to service. Also: when you want the same voltage from the same 
number of battery cells (say a NICd 12V pack).

Nickel-metal-hydride  or NiMH don't like to be completely discharged. 
They are more common these days of course, and have more power in a 
smaller package.

Lithium batteries were used for years in vintage computers, as clock and 
data backup power in tiny cells (Apple Macintosh computers). I believe 
many of the coin-cells are lithium. They are not rechargable, they have 
a VERY long shelf life. But the cylindrical-type (look like fractional 
AAA or AA batteries) sometimes  leak, and when they do it's a gooey 
awful mess. The 1990 lithium removable cells, seem to leak more than the 
1980's wired-in lithium cells. They have specific voltages per cell and 
package, so pay attention to both when replacing.

A side issue: the constant voltage from these batteries, produces copper 
corrosion - that green powder stuff - on circuits. I see chips and PC 
boards with green on them. Not good, and scrubbing off the copper oxide 
just reveals bare copper which will corrode unless coated with 
something. Frankly- I advice removing these batteries from any computer, 
when you can operate it without one. Install it when using, if you 
insist on the correct date or have BIOS settings, etc.

All part of the fun of vintage computer repair. I enjoy the challenges 
and finding problems and fixes and work-arounds. That calls for 
understanding the fundamentals. That's how I work....

Herb Johnson



-- 
Herbert R. Johnson,  New Jersey USA
http://www.retrotechnology.com OR .net