4 May
2020
4 May
'20
8:10 p.m.
Hi all,
I now have just acquired a VT-100 and am in the process of checking it out.
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.
Many thanks and Cheers, Martin...
5 May
5 May
12:08 a.m.
New subject: Hopefully on topic
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
6:15 a.m.
New subject: Hopefully on topic
On 5/5/2020 2:08 AM, Brent Hilpert via cctalk wrote:
On 2020-May-04, at 8:10 PM, Martin Crockett via cctalk
wrote:
This same question with the same subject appeared on the S100 computers
mailing list. I replied there with basically the same conclusion, based
on my own schematic (and also with advice that this is a better place to
ask.). Maybe he has a spam filter issue, and so didn't get the reply?
"Yeah, that looks like it is the printset from bitsavers. Even smudged
it looked like C14 to me, and I confirmed it *IS* C14 on my very clear
but very slightly older printset: VT100-0-1 Rev. C July, 1978. (Could
probably figure it out by elimination, too. C6 is on the edge of the
board opposite the RS232 connector in both printsets. One could look
through the rest of the parts for the other C1x capacitors to eliminate
those as possibilities as well.
My printset (Rev W schematic for this board) does NOT show the C59 that
is on the bitsavers pritnset (later, rev. AA), next to C14, and the
schematic in that area varies as well. But its proximity to C59 pretty
much seals the deal (see below regarding the bitsavers schematic.)
C14 is 0.22uf, 50 V (+80%-20%), on both my printset and the bitsavers
printset.
To verify it is C14 on your board:
On *my* schematic (Rev W), one side goes to +12V, the other to E24
(NVRAM) pin 2, R67 (22K), one side of W7 (which goes to -23V) and the
collector of Q6 (2N3904)
On the *bitsavers* schematic (later, Rev AA), one side goes to ground
(instead of +12V), but the rest it the same as above.
Your board should have an indication of which circuit schematic it is.
So, its a bypass cap for the NVRAM. On older boards it bypasses to
+12V, and on newer boards it bypasses to ground, and C59 bypasses +12V
to ground as well, which seems like a sensible change. ;')
For future reference, when asking about DEC stuff, the classic computer
mailing list might get you an answer quicker. ;) "
JRJ
..
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
6:23 a.m.
New subject: Hopefully on topic
Hi all,
I apologise if I posted this request in the wrong forum, but I'm new to
this; not electronics, I've got over 30 years bench experience, but asking
for help :-)
The answer you have given me is perfect. It confirms my suspicions that it
is C14. Now I have a value, I'll check it out in the morning.
I appreciate your assistance.
Many thanks and Cheers, Martin
Sent from my Nokia 6110
On Tue, 5 May 2020, 22:45 Jay Jaeger, <cube1 at charter.net> wrote:
On 5/5/2020 2:08 AM, Brent Hilpert via cctalk wrote:
non-volatile RAM?
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 (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
This same question with the same subject appeared on the S100 computers
mailing list. I replied there with basically the same conclusion, based
on my own schematic (and also with advice that this is a better place to
ask.). Maybe he has a spam filter issue, and so didn't get the reply?
"Yeah, that looks like it is the printset from bitsavers. Even smudged
it looked like C14 to me, and I confirmed it *IS* C14 on my very clear
but very slightly older printset: VT100-0-1 Rev. C July, 1978. (Could
probably figure it out by elimination, too. C6 is on the edge of the
board opposite the RS232 connector in both printsets. One could look
through the rest of the parts for the other C1x capacitors to eliminate
those as possibilities as well.
My printset (Rev W schematic for this board) does NOT show the C59 that
is on the bitsavers pritnset (later, rev. AA), next to C14, and the
schematic in that area varies as well. But its proximity to C59 pretty
much seals the deal (see below regarding the bitsavers schematic.)
C14 is 0.22uf, 50 V (+80%-20%), on both my printset and the bitsavers
printset.
To verify it is C14 on your board:
On *my* schematic (Rev W), one side goes to +12V, the other to E24
(NVRAM) pin 2, R67 (22K), one side of W7 (which goes to -23V) and the
collector of Q6 (2N3904)
On the *bitsavers* schematic (later, Rev AA), one side goes to ground
(instead of +12V), but the rest it the same as above.
Your board should have an indication of which circuit schematic it is.
So, its a bypass cap for the NVRAM. On older boards it bypasses to
+12V, and on newer boards it bypasses to ground, and C59 bypasses +12V
to ground as well, which seems like a sensible change. ;')
For future reference, when asking about DEC stuff, the classic computer
mailing list might get you an answer quicker. ;) "
JRJ
1475
days inactive
1475
days old
3 comments
3 participants
participants (3)
-
bhilpert＠shaw.ca -
crockett.martin＠gmail.com -
cube1＠charter.net