28 Aug
2003
28 Aug
'03
7:10 a.m.
Hello,
Thanks to the help of several of you, I have, after
reparing the power supply, been able to verify that
the CPU is running, and using the .PDF service manual,
am able to get a signal on the video pin (8) after
replacing the contrast pot. However, the monitor
still produces no output. I have a couple of
questions:
1) Is there a SAMS or some other document that
discusses the monitor operation?
2) What's the simplest way to use an external monitor
for testing?
3) Does the monitor use the +12V line on the connector
from the CPU board for all its power, including the HV
converter?
Unfortunately I don't have an HV probe at the moment,
so I'm being cautious about poking around the CRT.
Thanks,
David.
28 Aug
28 Aug
7:22 a.m.
Hello,
Thanks to the help of several of you, I have, after
reparing the power supply, been able to verify that
the CPU is running, and using the .PDF service manual,
am able to get a signal on the video pin (8) after
replacing the contrast pot. However, the monitor
still produces no output. I have a couple of
questions:
1) Is there a SAMS or some other document that
discusses the monitor operation?
Yes, I'll have to dig for it in the rubble here.
2) What's the simplest way to use an external monitor
for testing?
Wasn't there some sort of video adapter that plugged in where the jumper
was on the front panel.. ISTR it was a standard b/w NTSC monitor. One of
the surplus electronics places in CA was selling said item for about $4 or
so.
3) Does the monitor use the +12V line on the connector
from the CPU board for all its power, including the HV
converter?
I'd have to check the schematic, but it sounds logical (sorry Spock!)
Unfortunately I don't have an HV probe at the moment,
so I'm being cautious about poking around the CRT.
Well, using a screwdriver, pry up the cap over the HV lead on the CRT so
you can get at the metal --- and draw an arc to see if HV is present. Use
an insulated screwdriver, and don't tie it to ground. You should see a
small arc of maybe 1/4" or so. Sometimes you can hear the static
electricity around the CRT when it powers up as well, but being that
small, might be hard to hear. Sometimes with the static electricity you
can feel your hairs react as you take the back of your knuckles or hand
over the screen
I'd look at HV, then the grid voltages at the CRT, and then the video
output transistor that drives the cathode for proper voltages, etc.
Thanks,
David.
Gary Hildebrand
St. Joseph, MO
10:11 a.m.
Unfortunately
I don't have an HV probe at the moment,
so I'm being cautious about poking around the CRT.
Well, using a screwdriver, pry up the cap over the HV lead on the CRT so
you can get at the metal --- and draw an arc to see if HV is present. Use an insulated screwdriver, and don't tie it to
ground. You should see a
Admittedly it's less likely to do damage if the screwdriver is earthed
through a high impedance (the handle and _you_ (!)), but I still wouldn't
risk it.
-tony
7:37 a.m.
1) Is there a SAMS or some other document that
discusses the monitor operation?
I have a tech manual that is a little different to
the one Al Kossow has on his site. It includes
some information about the little monitors (IIRC
it has, for example, the original manufacturer's
data). I'll happily upload to somewhere but the whole
lot is probably somewhere between 100MB and a whole
CD. It includes things like the User's Guide (which
you probably do not need right now).
2) What's the simplest way to use an external
monitor
for testing?
No idea. I do believe that you need to plug in a little
adapter on the front though and that must be done with
the power OFF.
Unfortunately I don't have an HV probe at the
moment,
so I'm being cautious about poking around the CRT.
Do you not have schematics in the pdfs you have?
Antonio
--
---------------
Antonio Carlini arcarlini(a)iee.org
28 Aug
28 Aug
10:08 a.m.
3) Does the monitor use the +12V line on the
connector
from the CPU board for all its power, including the HV
converter?
Quite likely it does (I've never seen an Osbourne...) Many mono monitors
run the line output stage (horizontal output stage) off 12V, and the
flyback transformer provides all the higher voltages.
Unfortunately I don't have an HV probe at the moment,
so I'm being cautious about poking around the CRT.
Even without an EHT probe you can check the electron gun voltages.
Assuming it's a 7 pin CRT (with a 12V supply, I'd expect this, since such
CRTs have 12V heaters). Firstly, I assume the heater is glowing.
The pinout of most CRTs is :
1 : Control grid (expect a -ve voltage up to about -100V here, adjustable
by the brightness control if there is on (NOT the contrast control)
2 : Cathode (expect about 70-80V here, maybe less)
3 : Heater
4 : Heater (Often one of these is grounded, the other had 12V DC on it)
5 : Control grid (see pin 1)
6 : Anode
7 : Anode (One of these is the 'focus' electrode, the other is connected
to the 'screen' control if there is one. Expect about 400V on the latter
and a bit more on the former).
If the anode voltages are present and look reasonable, then the line
output stage is probably operational.
-tony
7568
days inactive
7570
days old
6 comments
5 participants
participants (5)
-
arcarlini＠iee.org -
ard＠p850ug1.demon.co.uk -
dfnr2＠yahoo.com -
ghldbrd＠ccp.com -
patrick＠evocative.com