15 Jun
2009
15 Jun
'09
12:34 p.m.
Hi, All,
I'm going through piles of stuff at FreeGeek Columbus, identifying odd
stuff (since most of the volunteers are really only trained on
commodity PC hardware). We have a pile of DEC terminals and X Terms
from a local car dealer. The VT220s are, of course,
easy to plug in
and test. There is another terminal, though, that's clearly of
DEC
origin, but I can't find how to get into 'setup' mode.
The terminals are marked on the front "505 MT", and on the back, the
DEC label says something like "VT-42 - 505 MT". Physically, they look
newer than a VT220 and sort-of resemble a Wyse 50. When powering them
on, they appear to have some sort of graphic video memory test on
startup. The same LK-series keyboard (not an LK-201, but something in
the LK-4xx line) that works find with the VT220s does not give me the
setup menu on the 505 MT from pressing F3.
From interpreting the 2-3 labels on the top, back and
sometimes sides,
it wouldn't surprise me that these are VT-420s with some sort
of
custom firmware for an ADP system of some kind. I've done some
googling, but haven't turned up much except for replacement prices.
All of these terminals are dirty and the plastic yellowed with age/UV
exposure, but once I get them all checked out, FreeGeek Columbus is
interested in selling them for a nominal amount (under $50). There
are no keyboards or power cords, and they will all need to be cleaned,
but I can say that each one sold will be tested (by me) to work with
an LK-series keyboard and have stable video (VT220s have a common
fault that takes out horizontal hold) and working serial line drivers
(tested with a loopback plug).
If anyone recognizes a "505 MT" variant of a VT420 and especially
knows how to get into setup, I'd love to hear from you. If anyone is
interested in one of these terminals (sans keyboard), I'd love to hear
from you on that, too. FreeGeek Columbus would like to
place these
terminals into loving homes and not have to scrap them.
Thanks,
-ethan
4:22 p.m.
I'm sorry for hi-jacking this topic but,
Most of the time it's just a bad contact at the wiper of the horizontal
hold preset inside.
Take off the terminal cover (extend the 'leg' all the way down, put the
terminal on it's screen, take off the 3 (?) plastic caps and undo the
screws under them).
The horizontal hold preset is marked on the paper cover on the video PCB.
Note its position, then turn it several times from one end to the other.
Put it back to the original position.
Plug the terminal into the mains and power up (you don't need a
keyboard). If the picture locks, power down amd put the cover on. If not,
turn the horizotnal hold preset until it does, and set it to the middle
of the range where the picture is locked. Power down, wait a bit, power
up nd check it locks. Then power down again and put the cover on.
If you can't get the picture to lock by adjusting the preset, then you
have a more tricky fault to find :-)
-tony
(VT220s have a common fault that takes out
horizontal hold)
I think my VT220 has this problem, is there any documentation regarding
diagnosing and fixing this problem? I have search to no avail. 
16 Jun
16 Jun
4:14 p.m.
Tony Duell wrote:
(yes, its three of them)
I'm sorry
for hi-jacking this topic but,
Most of the time it's just a bad contact at the wiper of the horizontal
hold preset inside.
Take off the terminal cover (extend the 'leg' all the way down, put the
terminal on it's screen, take off the 3 (?) plastic caps and undo the
screws under them).
(VT220s have a common fault that takes out
horizontal hold)
I think my VT220 has this problem, is there any documentation regarding
diagnosing and fixing this problem? I have search to no avail.
The horizontal hold preset is marked on the paper
cover on the video PCB.
Note its position, then turn it several times from one end to the other.
Put it back to the original position.
I could not find a paper cover, but it is printed on the PCB.
Plug the terminal into the mains and power up (you
don't need a
keyboard). If the picture locks, power down amd put the cover on. If not,
turn the horizotnal hold preset until it does, and set it to the middle
of the range where the picture is locked. Power down, wait a bit, power
up nd check it locks. Then power down again and put the cover on.
If you can't get the picture to lock by adjusting the preset, then you
have a more tricky fault to find :-)
-tony
My memory served me wrong, or I read the post to fast. Is the symptoms
of a "lost" horizontal hold that the picture will scroll, looping around?
This vt220 in front of me has no picture at all. I was using it and
between the blink of my eyes the picture disappeared, no bang, no smoke,
just gone. I think the logic still works, judging by the led indicators
on the keyboard and the satisfying beep it "boots" just fine.
Any ideas where I should start looking?
Kind regards,
Pontus.
4:30 p.m.
On Tue, Jun 16, 2009 at 4:14 PM, Pontus<pontus at update.uu.se> wrote:
Vertical hold problems are what I would describe as scrolling and
looping. Horizontal hold problems are where the picture breaks from
left to right and tears diagonally.
Tony Duell wrote:
>> I'm sorry for hi-jacking this topic but,
>>
>>> (VT220s have a common fault that takes out horizontal hold)
>
> Most of the time it's just a bad contact at the wiper of the horizontal
> hold preset inside.
Plug the
terminal into the mains and power up (you don't need a
keyboard). If the picture locks, power down amd put the cover on....
If you can't get the picture to lock by adjusting the preset, then you
have a more tricky fault to find :-)
My memory served me wrong, or I read the post to fast. Is the symptoms
of a "lost" horizontal hold that the picture will scroll, looping around?
This vt220 in front of me has no picture at all. I was
using it and
between the blink of my eyes the picture disappeared, no bang, no smoke,
just gone. I think the logic still works, judging by the led indicators
on the keyboard and the satisfying beep it "boots" just fine.
Any ideas where I should start looking?
Me? Besides checking for reasonable voltages at the digital board?
Not really. I'm just fine with diagnosing digital logic, but not so
good with video.
-ethan
5:13 p.m.
On Tue, Jun 16, 2009 at 4:14 PM, Pontus<pontus at
update.uu.se> wrote:
> This vt220 in front of me has no picture at all. I was using it and
> between the blink of my eyes the picture disappeared, no bang, no
> smoke, just gone. I think the logic still works, judging by the led
> indicators on the keyboard and the satisfying beep it "boots" just
> fine.
>
> Any ideas where I should start looking?
Yeah, probably start with the horizontal output transistor (HOT), and
flyback. I'm sure Tony will be helpful in pointing you in the right
direction. I haven't run across a broken VT220 (nor needed one badly
enough to consider fixing it).
Pat
--
Purdue University Research Computing --- http://www.rcac.purdue.edu/
The Computer Refuge --- http://computer-refuge.org
5:22 p.m.
On Tue, 2009-06-16 at 22:14 +0200, Pontus wrote:
This vt220 in front of me has no picture at all. I was
using it and
between the blink of my eyes the picture disappeared, no bang, no smoke,
just gone. I think the logic still works, judging by the led indicators
on the keyboard and the satisfying beep it "boots" just fine.
Any ideas where I should start looking?
Hang a TV off the BNC video connector on the back, with a suitable set
of adaptors.
If you get that far, you've got some sort of video happening.
Gordon
17 Jun
17 Jun
4:22 p.m.
New subject: repairing VT220 DEC terminal -
Gordon JC Pearce wrote:
Hang a TV off the BNC video connector on the back,
with a suitable set
of adaptors.
If you get that far, you've got some sort of video happening.
Gordon
This got me going :) I search high an low for a "suitable set of
adaptors" when I noticed that my vt125 has a video in and I hooked them
up. It showed me this:
http://www.update.uu.se/~pontus/slask/vt220-125.jpg
The video signal is obviously not syncing up, but you can clearly read
"VT220 OK". So the logic board is fine. I guess I should start looking
for the HOT, the flyback looks ok, not like the broken ones I've seen in
a vt320.
I could not find any fuses on the video board as mentioned by Jerry. But
I believe there was at least two revisions of the vt220 video board.
Cheers,
Pontus.
5:11 p.m.
New subject: repairing VT220 DEC terminal -
On Jun 17, 2009, at 4:22 PM, Pontus wrote:
This got me going :) I search high an low for a
"suitable set of
adaptors" when I noticed that my vt125 has a video in and I hooked
them
up. It showed me this:
http://www.update.uu.se/~pontus/slask/vt220-125.jpg
Wow, that's an image straight out of The Twilight Zone. ;)
The video signal is obviously not syncing up, but you
can clearly read
"VT220 OK". So the logic board is fine. I guess I should start looking
for the HOT, the flyback looks ok, not like the broken ones I've
seen in
a vt320.
Yup, sure sounds like "an analog failure" (not that there's any
other kind) in the monitor section. The monitor circuits in the
VT220 are fairly simple, aren't they?
-Dave
--
Dave McGuire
Port Charlotte, FL
18 Jun
18 Jun
1:57 p.m.
New subject: repairing VT220 DEC terminal -
This got me
going :) I search high an low for a "suitable set of
adaptors" when I noticed that my vt125 has a video in and I hooked
them
up. It showed me this:
http://www.update.uu.se/~pontus/slask/vt220-125.jpg
Wow, that's an image straight out of The Twilight Zone. ;) The video signal is obviously not syncing up, but
you can clearly read
"VT220 OK". So the logic board is fine. I guess I should start looking
for the HOT, the flyback looks ok, not like the broken ones I've
seen in
a vt320.
Yup, sure sounds like "an analog failure" (not that there's any
other kind) in the monitor section. The monitor circuits in the
VT220 are fairly simple, aren't they? 
17 Jun
17 Jun
5:30 p.m.
New subject: repairing VT220 DEC terminal -
In article <4A39506C.1040801 at update.uu.se>,
Pontus <pontus at update.uu.se> writes:
This got me going :) I search high an low for a
"suitable set of
adaptors" when I noticed that my vt125 has a video in and I hooked them
up. It showed me this:
http://www.update.uu.se/~pontus/slask/vt220-125.jpg
shell 41> wget http://www.update.uu.se/~pontus/slask/vt220-125.jpg
--15:29:57-- http://www.update.uu.se/~pontus/slask/vt220-125.jpg
=> `vt220-125.jpg'
Resolving www.update.uu.se... 130.238.19.25
Connecting to www.update.uu.se|130.238.19.25|:80... failed: Connection refused.
--
"The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download
<http://www.xmission.com/~legalize/book/download/index.html>
Legalize Adulthood! <http://blogs.xmission.com/legalize/>
18 Jun
18 Jun
2:41 a.m.
New subject: repairing VT220 DEC terminal -
On Wed, Jun 17, 2009 at 03:30:18PM -0600, Richard wrote:
shell 41> wget http://www.update.uu.se/~pontus/slask/vt220-125.jpg
--15:29:57-- http://www.update.uu.se/~pontus/slask/vt220-125.jpg
=> `vt220-125.jpg'
Resolving www.update.uu.se... 130.238.19.25
Connecting to www.update.uu.se|130.238.19.25|:80... failed: Connection refused.
Quite typical, that server has had a lot of problems with a disk
controller, about ten minutes after I uploaded the image it took a nose
dive. Try again, it should be fine :)
/P
16 Jun
16 Jun
7:17 p.m.
New subject: repairing VT220 DEC terminal -
-------------- Original message from Pontus <pontus at update.uu.se>:
--------------
My memory served me wrong, or I read the post to fast. Is the symptoms
of a "lost" horizontal hold that the picture will scroll, looping around?
This vt220 in front of me has no picture at all. I was using it and
between the blink of my eyes the picture disappeared, no bang, no smoke,
just gone. I think the logic still works, judging by the led indicators
on the keyboard and the satisfying beep it "boots" just fine.
I believe I did 2 of these last year and they had a fuse on the mother
board ??? both of them where blown and replacing them only blew
another fuse.
Turned out to be a capacitor on both that was shorted. I'm at work
and can't check my notes. Do remember it was a non polarized cap.
- jerry
Any ideas where I should start looking?
Kind regards,
Pontus.
17 Jun
17 Jun
2:21 p.m.
My memory served me wrong, or I read the post to fast.
Is the symptoms
of a "lost" horizontal hold that the picture will scroll, looping around?
No, that's loss of _vertical_ hold. Loss of horizontal hold wil lcause
the picture to break up into sloping lines across the screen.
This vt220 in front of me has no picture at all. I was using it and
between the blink of my eyes the picture disappeared, no bang, no smoke,
just gone. I think the logic still works, judging by the led indicators
on the keyboard and the satisfying beep it "boots" just fine.
Any ideas where I should start looking?
Do you have a composite video monitor around? If so, connect it to the
BNC socket on the back of the VT220. If you get a display on that
monitor, the VT220 logic is working.
An old book on TV servicing (so old that it doesn't mention transistors,
and even disccussed mains-derrived rather than flyback EHT...) points out
that there are 7 signals applied to a CRT (this applies to monitors and
terminals too)
1) Heater supply
2) Video drive
3) Grid bias
4) First anode voltage and/or focus voltage
5) Horizontal deflection
6) Vertical drfleciton
7) Final anode voltage (EHT)
Problems with any of them can result in a blank screen, although problems
with _just_ the deflection [1] would have to involve steady DC currents
through the coils to deflect the beam off-screen, which is a very
uncommon fault.
[1] Note that in just about every monitor/terminal (and certainly the
VT220), the EHT and other CRT supplies come from the horizontal output
stage. A faut in the horizontal deflection circuit may well remove these
voltages and cause the screen to go blank.
So it's basically a process of finding out which input is wrong and
correcting it. I'd start by checking the CRT heater is glowing (it's easy
to do -- just look at it), and then, assuming you have a suitable EHT
meter, measure the final anode voltage. Expect about 10kV here.
Alas without schematics it's difficult to go much further -- is the VT220
printset on a web site?
-tony
5:18 p.m.
On Wed, Jun 17, 2009 at 2:21 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Alas without schematics it's difficult to go much
further --
That is sort of where I'm stuck. I can follow schematics and trace
along just fine, but my knowledge of video is somewhat spotty - some
problems I can probably find and correct quite easily, others leave me
scratching my head.
is the VT220 printset on a web site?
I have never seen one, but hopefully it's because I'm just not looking
in the right place. If anyone knows where, I'd love to get a pointer.
-ethan
15 Jun
15 Jun
2:37 p.m.
It would not have been unusual for DEC to have sold terminals to OEM's who
then modified them for their own systems. I did just that whilst working
for DEC. We even sold LA36 print mechanisms to a company who added their own
electronics and tape reader/punches.
Regards
Rod Smallwood
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Ethan Dicks
Sent: 15 June 2009 17:34
To: classiccmp at classiccmp.org
Subject: Unusual semi-modern DEC terminal - "MT 505"?
Hi, All,
I'm going through piles of stuff at FreeGeek Columbus, identifying odd
stuff (since most of the volunteers are really only trained on
commodity PC hardware). We have a pile of DEC terminals and X Terms
from a local car dealer. The VT220s are, of course,
easy to plug in
and test. There is another terminal, though, that's clearly of
DEC
origin, but I can't find how to get into 'setup' mode.
The terminals are marked on the front "505 MT", and on the back, the
DEC label says something like "VT-42 - 505 MT". Physically, they look
newer than a VT220 and sort-of resemble a Wyse 50. When powering them
on, they appear to have some sort of graphic video memory test on
startup. The same LK-series keyboard (not an LK-201, but something in
the LK-4xx line) that works find with the VT220s does not give me the
setup menu on the 505 MT from pressing F3.
From interpreting the 2-3 labels on the top, back and
sometimes sides,
it wouldn't surprise me that these are VT-420s with some sort
of
custom firmware for an ADP system of some kind. I've done some
googling, but haven't turned up much except for replacement prices.
All of these terminals are dirty and the plastic yellowed with age/UV
exposure, but once I get them all checked out, FreeGeek Columbus is
interested in selling them for a nominal amount (under $50). There
are no keyboards or power cords, and they will all need to be cleaned,
but I can say that each one sold will be tested (by me) to work with
an LK-series keyboard and have stable video (VT220s have a common
fault that takes out horizontal hold) and working serial line drivers
(tested with a loopback plug).
If anyone recognizes a "505 MT" variant of a VT420 and especially
knows how to get into setup, I'd love to hear from you. If anyone is
interested in one of these terminals (sans keyboard), I'd love to hear
from you on that, too. FreeGeek Columbus would like to
place these
terminals into loving homes and not have to scrap them.
Thanks,
-ethan
16 Jun
16 Jun
2:04 p.m.
In article <f4eb766f0906150934ib1ed624gc8fe46fdef2d88dd at mail.gmail.com>,
Ethan Dicks <ethan.dicks at gmail.com> writes:
The terminals are marked on the front "505
MT", and on the back, the
DEC label says something like "VT-42 - 505 MT".
Never heard of either a 505 MT or a VT-42. Sounds like an OEM job as
someone else suggested.
--
"The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download
<http://www.xmission.com/~legalize/book/download/index.html>
Legalize Adulthood! <http://blogs.xmission.com/legalize/>
5508
days inactive
5511
days old
16 comments
9 participants
participants (9)
-
ard＠p850ug1.demon.co.uk -
ethan.dicks＠gmail.com -
g-wright＠att.net -
gordonjcp＠gjcp.net -
legalize＠xmission.com -
mcguire＠neurotica.com -
pat＠computer-refuge.org -
pontus＠update.uu.se -
rodsmallwood＠btconnect.com