[vcf-midatlantic] [Off Topic] - Vintage computers and UPSes

Herb Johnson hjohnson at retrotechnology.info
Tue Aug 20 14:23:12 EDT 2019

I think this subject is on-topic, because vintage computers suffer 
damage over time due to line-voltage and over-voltage. UPSs can't solve 
all those problems. But paying attention to the AC power line is 
important to collectors and users.

Shorted tantalum capacitors on DC circuits are a known failure due to 
both time and over voltage. For example, Heath/Zenith H-89s and H-19s 
(computer and terminal) expect to operate at 110V AC.T he unregulated 
side of their 5V DC regulators have capacitors rated at a voltage just 
below the DC voltage produced - at 110V. When run at 120V or higher, 
the rated voltage is exceeded and the tantalums "blow". The fix is to 
replace the caps with higher-voltage devices, and/or reduce AC voltage.

That solution won't be found with most UPS. A short-term solution is to 
use a Variac to reduce AC voltage. Long term, there's step-up/down 
transformers one can buy for the purpose. Technically-experienced people 
can make such devices.

also: Thank you to Jason Perkins, for his post-link to an article on 
adjusting a UPS charging voltage. I was aware of this problem but not 
informed in detail. The article is informative, so thanks!


Herb Johnson

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

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