HP-35 power unit: Failing Vgg voltage

[robjordan]

Sure enough there must have been a broken connection between one of the wires and the body of the transformer. After I'd desoldered it from the board and pulled it out, the break became obvious. Fixed that, and Vgg is produced, and the machine came to life! Probably the first time in 40 years that the LEDs had been illuminated. All voltages are a bit low, but that didn't seem to cause any functional problem (7.3V, 5.7V and -10.7V).

Unfortunately it's not the whole story because when I reassembled I find I have problems with the power switch, and some of the keys are erratic, but it's a huge breakthrough.

Incidentally, this calculator has no transparent foil over the keyboard like all the others I've seen pictured. Does the foil serve any purpose other than protective?

Thanks
Rob