Hopefully on topic

Brent Hilpert bhilpert at shaw.ca
Tue May 5 02:08:22 CDT 2020

On 2020-May-04, at 8:10 PM, Martin Crockett via cctalk wrote:
> ..
> I noticed there is a capacitor that has vaporized, but I cant determine
> what value it is.
> I have the DEC VT-100 maintenance guide but it is very blurry in the
> relevant area.
> I cant even read the board designation.
> This is the area of the circuit, I can trace the 2 Zener diodes on the -23V
> rail, to one end of the cap, the other end seems to go to ground. The
> obvious culprit is C6, but that doesn't match the mud map of the board, as
> in C1x.
> https://imgur.com/a/tm8mn8b
> This is the capacitor in question.
> It looks like C1x where x is undetermined.
> I think it was a ceramic monolithic capacitor, it seems to be different to
> any other caps on the board, i.e. slightly larger and a different colour
> blue. When I look at this hires photos on Google images, it is the blue
> capacitor circled below
> Does anyone have a VT-100 and mind checking what the value of this
> capacitor is please?
> Ideally value and voltage or even just the nomenclature written on it, I
> can work out the value and voltage from that.

You sure that isn't C14, connected to pin 2 of E24, Vgg PS pin on the non-volatile RAM?
(bitsavers schematic pdf pg 15 / "VT100 BASIC VIDEO Sheet 2 of 6" / upper middle of page).
See also the board pics on bitsavers.

0.22uF, 50V CER

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