HP-35 power unit: Failing Vgg voltage

[teenix]

Low voltages may be from some of the power supply capacitors starting to fail due to age but can be replaced easily if desired.

The plastic serves to stop dust and a small amount of liquid from getting on the key contacts and is wise to be fitted. Cutting up a zip lock lunch bag should serve ok.

Page 42 of my Classic Notes PDF file describes a cleaning method for the keys.

HP put some switch lubricant on the power switch during manufacture and this has probably hardened over the years and is interfering with proper contact now.

Just clean the contact and circuit board area with isopropyl alcohol. A lot of hobby shops sell silicon switch grease in small tubes, or more expensive ones at Digikey, Mouser etc. If you don't have any proper switch lube, a "tiny" amount of vaseline (petroleum jelly) smeared on the circuit board contacts will suffice.

cheers

Tony