29 Aug
2015
29 Aug
'15
6:07 p.m.
Hi all,
I am trying to identify why my IBM 5151 display has no picture when
connected to a normal MDA card in a IBM PC 5150. So armed with an
oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
started to investigate. First, the card does send out signal and that
signal does reach the board inside the monitor. I checked the power
part of the circuit, all diodes and the transistor check fine. I
probed some of the vertical and horizontal transistors and there is a
signal there too. Then on the video board both TR19 and TR20 have on
their collector and emitter (respectively) a signal (95Khz). What else
can possibly be wrong?
The SAMS manual talks about "injecting a video signal" at different
pins however I have no idea exactly how to do that.
So there is current going out of the power part and there is signal on
the video board attached to the neck of the CRT.
Regards,
Vlad.
29 Aug
29 Aug
6:17 p.m.
There is a 2nd connector for the video card of the 5151. I can't quite tell
if you mean you have the video card that comes with the 5155 and you're
trying to test with a card that came from somewhere else or something else.
I am unsure if the 2nd connector pertains to the internal or external port,
but you want to be sure you have this in place.
.
http://vintagecomputer.net/ibm/5155/ibm5155_monitor_connector_cga_card_clos…
On Sat, Aug 29, 2015 at 9:07 PM, Vlad Stamate <vlad.stamate at gmail.com>
wrote:
Hi all,
I am trying to identify why my IBM 5151 display has no picture when
connected to a normal MDA card in a IBM PC 5150. So armed with an
oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
started to investigate. First, the card does send out signal and that
signal does reach the board inside the monitor. I checked the power
part of the circuit, all diodes and the transistor check fine. I
probed some of the vertical and horizontal transistors and there is a
signal there too. Then on the video board both TR19 and TR20 have on
their collector and emitter (respectively) a signal (95Khz). What else
can possibly be wrong?
The SAMS manual talks about "injecting a video signal" at different
pins however I have no idea exactly how to do that.
So there is current going out of the power part and there is signal on
the video board attached to the neck of the CRT.
Regards,
Vlad.
--
Bill
vintagecomputer.net
6:24 p.m.
I have a normal IBM PC 5150 (not a 5155) with the usual MDA card
inside. So when the computer is on, no picture comes on the monitor.
So I am trying to diagnose that.
(on a side note I do have a few of both monochrome cards as well as
another IBM PC XT - 5160 as well as 2 other 286 based machines I can
try, just in case the issue is NOT with the monochrome monitor but
with the card/PC assembly).
Regards,
Vlad.
On 29 August 2015 at 21:17, william degnan <billdegnan at gmail.com> wrote:
There is a 2nd connector for the video card of the
5151. I can't quite tell
if you mean you have the video card that comes with the 5155 and you're
trying to test with a card that came from somewhere else or something else.
I am unsure if the 2nd connector pertains to the internal or external port,
but you want to be sure you have this in place.
.
http://vintagecomputer.net/ibm/5155/ibm5155_monitor_connector_cga_card_clos…
On Sat, Aug 29, 2015 at 9:07 PM, Vlad Stamate <vlad.stamate at gmail.com>
wrote:
Hi all,
I am trying to identify why my IBM 5151 display has no picture when
connected to a normal MDA card in a IBM PC 5150. So armed with an
oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
started to investigate. First, the card does send out signal and that
signal does reach the board inside the monitor. I checked the power
part of the circuit, all diodes and the transistor check fine. I
probed some of the vertical and horizontal transistors and there is a
signal there too. Then on the video board both TR19 and TR20 have on
their collector and emitter (respectively) a signal (95Khz). What else
can possibly be wrong?
The SAMS manual talks about "injecting a video signal" at different
pins however I have no idea exactly how to do that.
So there is current going out of the power part and there is signal on
the video board attached to the neck of the CRT.
Regards,
Vlad.
--
Bill
vintagecomputer.net
6:27 p.m.
often the card is the culprit, sometimes shorting out the entire sytem.
On Sat, Aug 29, 2015 at 9:24 PM, Vlad Stamate <vlad.stamate at gmail.com>
wrote:
I have a normal IBM PC 5150 (not a 5155) with the
usual MDA card
inside. So when the computer is on, no picture comes on the monitor.
So I am trying to diagnose that.
(on a side note I do have a few of both monochrome cards as well as
another IBM PC XT - 5160 as well as 2 other 286 based machines I can
try, just in case the issue is NOT with the monochrome monitor but
with the card/PC assembly).
Regards,
Vlad.
On 29 August 2015 at 21:17, william degnan <billdegnan at gmail.com> wrote:
--
Bill
vintagecomputer.net
There is a 2nd connector for the video card of
the 5151. I can't quite
tell
if you mean you have the video card that comes
with the 5155 and you're
trying to test with a card that came from somewhere else or something
else.
I am unsure if the 2nd connector pertains to the
internal or external
port,
but you want to be sure you have this in place.
.
http://vintagecomputer.net/ibm/5155/ibm5155_monitor_connector_cga_card_clos…
On Sat, Aug 29, 2015 at 9:07 PM, Vlad Stamate <vlad.stamate at gmail.com>
wrote:
Hi all,
I am trying to identify why my IBM 5151 display has no picture when
connected to a normal MDA card in a IBM PC 5150. So armed with an
oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
started to investigate. First, the card does send out signal and that
signal does reach the board inside the monitor. I checked the power
part of the circuit, all diodes and the transistor check fine. I
probed some of the vertical and horizontal transistors and there is a
signal there too. Then on the video board both TR19 and TR20 have on
their collector and emitter (respectively) a signal (95Khz). What else
can possibly be wrong?
The SAMS manual talks about "injecting a video signal" at different
pins however I have no idea exactly how to do that.
So there is current going out of the power part and there is signal on
the video board attached to the neck of the CRT.
Regards,
Vlad.
--
Bill
vintagecomputer.net 
6:33 p.m.
On Sat, 29 Aug 2015, william degnan wrote:
often the card is the culprit, sometimes shorting out
the entire sytem.
Absolutely!
And, if the motherboard is set for CGA, instead of MDA, the board might
not come up. BUT, he did say that he had what the thought might be video
signals reaching the monitor.
In addition, VGA boards can be problematic in configuration. When
bringing up a PC of those vintages, I try to always start with a CGA board
and appropriate monitor. THEN, once that is working, THEN put the VGA in.
6:29 p.m.
> I am trying to identify why my IBM 5151 display
has no picture when
> connected to a normal MDA card in a IBM PC 5150. So armed with an
On Sat, 29 Aug 2015, william degnan wrote:
There is a 2nd connector for the video card of the
5151.
5151 is a monitor number.
I can't quite tell
if you mean you have the video card that comes with the 5155 and you're
trying to test with a card that came from somewhere else or something else.
I am unsure if the 2nd connector pertains to the internal or external port,
but you want to be sure you have this in place.
http://vintagecomputer.net/ibm/5155/ibm5155_monitor_connector_cga_card_clos…
He said 5151 connected to MDA in 5150. That would have little or no
overlap with what the 5155 has.
The 5155 does not use an MDA, although one COULD be added for a second
monitor. The 5155 uses CGA. The CGA has three video outs. There is a
DE9 RGB video out, for color monitors. Should never be connected to a
5151 or other MDA/MONO(MDA)/Hercules monitor!
The CGA also has an RCA with composite (almost RS-170) video out.
And, the CGA has, just inside the bracket, a 4 pin sometimes keyed Berg
connector that was originally intended for an RF modulator such as the
SUP'R'MODII. That connector has voltage and composite, and is used in the
5155 for the internal monitor.
The CGA also has a 6 pin Berg connector for light-pen.
He said 5151 connected to MDA in 5150. So, none of the CGA stuff applies.
The MDA board, has a DE9 for IBM MDA MONO (sometimes called "Hercules" in
a futile attempt to avoid ambiguity).
The IBM MDA board also has a DB25 parallel printer port (sometimes
erroneously called "Centronics"). Hence, the IBM board is called MDP, and
there are many AFTER-market MDA boards.
Some of the IBM MDA boards have a light-pen connector?
11:36 p.m.
I am trying to identify why my IBM 5151 display has no
picture when
connected to a normal MDA card in a IBM PC 5150. So armed with an
oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
started to investigate. First, the card does send out signal and that
signal does reach the board inside the monitor. I checked the power
part of the circuit, all diodes and the transistor check fine. I
probed some of the vertical and horizontal transistors and there is a
signal there too. Then on the video board both TR19 and TR20 have on
their collector and emitter (respectively) a signal (95Khz). What else
can possibly be wrong?
Do you mean no picture or no raster? To me the 'picture' is the video
modulation (that makes different bits of the screen light or dark). If you
turn up the brightness and contrast controls do you get any illumination on
the screen?
I am going to assume you don't, since that is the more common problem.
First check the internal 12V (or so) supply. Is that present and correct. Note
it mght be low due to an overload somewhere else in the monitor, for
example flyback transformer problems.
Is the CRT heater glowing (can you see an orange glow from the end of the
CRT neck)? If not, and if the 12V supply is there, then check the CRT and its
socket. There may be a series resistor too, check that.
Now check the CRT voltages. If you have an EHT meter, check the final
anode voltage (on the rubber connector on the CRT flare). Expect
about 10-12kV here.
The CRT pins (from memory) are as follows (All voltages guessed wrt ground):
1: Control grid (10's of V, +ve or -ve)
2: Cathode (10's of V +ve)
3,4 : heater. One is ground, expect 12V or so on the other
5: Control grid (see pin 1)
6,7 : I call them anodes, you call them grids :-). Expect a few hunded volts on each pin.
What voltages do you measure?
-tony
30 Aug
30 Aug
1:22 p.m.
Hi,
Thank you for answering, I appreciate your help. Answers inline below.
On Aug 30, 2015, at 2:36 AM, tony duell <ard at
p850ug1.demon.co.uk> wrote:
The screen is entirely black no matter what I do with brightness and
contrast controls.
I am trying to identify why my IBM 5151 display
has no picture when
connected to a normal MDA card in a IBM PC 5150. So armed with an
oscilloscope, digital multi-meter and the SAMS Computerfacts for it I
started to investigate. First, the card does send out signal and that
signal does reach the board inside the monitor. I checked the power
part of the circuit, all diodes and the transistor check fine. I
probed some of the vertical and horizontal transistors and there is a
signal there too. Then on the video board both TR19 and TR20 have on
their collector and emitter (respectively) a signal (95Khz). What else
can possibly be wrong?
Do you mean no picture or no raster? To me the 'picture' is the video
modulation (that makes different bits of the screen light or dark). If you
turn up the brightness and contrast controls do you get any illumination on
the screen?
I am going to assume you don't, since that is the more common problem.
First check the internal 12V (or so) supply. Is that present and correct. Note
it mght be low due to an overload somewhere else in the monitor, for
example flyback transformer problems.
I am getting 14V out of the transistor in the
power supply. Voltages seem to check correct there according to the SAMS schematic. Except
for one point earlier in the power supply that is supposed to be 25.9V but I get 28V.
Is the CRT heater glowing (can you see an orange glow from the end of the
CRT neck)? If not, and if the 12V supply is there, then check the CRT and its
socket. There may be a series resistor too, check that.
I see the orange glow.
Now check the CRT voltages. If you have an EHT meter, check the final
anode voltage (on the rubber connector on the CRT flare). Expect
about 10-12kV here.
I do not have a tool that can measure that high of a voltage.
The CRT pins (from memory) are as follows (All voltages guessed wrt ground):
1: Control grid (10's of V, +ve or -ve)
225mV
2: Cathode (10's of V +ve)
170mV
3,4 : heater. One is ground, expect 12V or so on the
other
3: 12V
4: Ground
5: Control grid (see pin 1)
225mV
6,7 : I call them anodes, you call them grids :-).
Expect a few hunded volts on each pin.
6: 7.33V
7: 10.29V
What voltages do you measure?
I checked all those with respect to ground ( pin 4).
Regards,
Vlad.
-tony
1:29 p.m.
Do you mean no
picture or no raster? To me the 'picture' is the video
modulation (that makes different bits of the screen light or dark). If you
turn up the brightness and contrast controls do you get any illumination on
the screen?
The screen is entirely black no matter what I do with brightness and
contrast controls. The CRT pins
(from memory) are as follows (All voltages guessed wrt ground):
1: Control grid (10's of V, +ve or -ve)
225mV
2: Cathode (10's of V +ve)
170mV
3,4 : heater. One is ground, expect 12V or so on
the other
3 : 12V
4: Ground
5: Control grid (see pin 1)
225mV
6,7 : I call them anodes, you call them grids
:-). Expect a few hunded volts on each pin.
6: 7.33V
7: 10.29V
What voltages do you measure?
I checked all those with respect to ground ( pin 4).
-tony
4:36 p.m.
Hi Tony,
I have checked the horizontal signal from the MDA using an
oscilloscope. It is pin 8 like you mentioned. I get a regular 18KHz or
so signal out of that. Pin 9 gives the vertical signal at roughly
50Hz.
Then I traced that on the board and it seems ok (as in I can see the
18Khz signal on other components). One thing that I noticed is that
Pin 6 of the CRT neck comes pretty much from one of the pins of the
flyback transformer (via some diodes and resistors). So I checked the
voltage on the pins of the flyback transformer itself, so here is how
it looks
1 and 8 - Not connected
2 and 4 (I think those are inputs) - 15V
3 - GND
5 - 15V (this one goes to pin 6 of the video board where you mentioned
it should be hundreds of volts)
6 and 7 - about 200mV.
Does that look correct to you?
Regards,
Vlad.
On 30 August 2015 at 16:29, tony duell <ard at p850ug1.demon.co.uk> wrote:
OK.... Given the CRT voltages you give later, I would expect that.
Well, all the electrode votlages are very low.
They all come from the flyback transformer in the horizontal output stage. Now the 5151
is
unusual in that it doesn't have a horizontal oscillator. The horizontal signal from
the MDA
card goes straight to the horizontal driver which, IIRC, is transformer coupled to the
horizontal output transistor.
So, start by checking you have a horizontal signal from the MDA card. I think it's
pin 8 of
the DE9, if not it's pin 9, the other being the vertical sync signal. If that's
present and correct
check through the driver and output stages, there are not that many components.
If it is transformer coupled, then I have had those driver transformers go open-circuit
in
monitors -- not in the 5151 yet, but it could happen.
-tony
Regards,
Vlad.
>
> -tony
Do you
mean no picture or no raster? To me the 'picture' is the video
modulation (that makes different bits of the screen light or dark). If you
turn up the brightness and contrast controls do you get any illumination on
the screen?
The screen is entirely black no matter what I do with brightness and
contrast controls. The CRT
pins (from memory) are as follows (All voltages guessed wrt ground):
1: Control grid (10's of V, +ve or -ve)
225mV
2: Cathode (10's of V +ve)
170mV
3,4 : heater. One is ground, expect 12V or so on
the other
3 : 12V
4: Ground
5: Control grid (see pin 1)
225mV
6,7 : I call them anodes, you call them grids
:-). Expect a few hunded volts on each pin.
6: 7.33V
7: 10.29V
What voltages do you measure?
I checked all those with respect to ground ( pin 4).
11:26 p.m.
Hi Tony,
I have checked the horizontal signal from the MDA using an
oscilloscope. It is pin 8 like you mentioned. I get a regular 18KHz or
so signal out of that. Pin 9 gives the vertical signal at roughly
50Hz.
OK. Your PC and MDA card seem to be OK.
Now trace through the horizontail circuit in the 5151. IIRC there
is a driver transistor, the collector load of which is a transformer
which couples to the base of the horizontal output transistor
(sorry, I am doing this from memory, I don't have the techref
in front of me). Do you get the 18kHz on the collector of
the driver transistor?
Are both transistors good?
-tony
31 Aug
31 Aug
3:18 p.m.
Hi,
I traced the 18Khz signal all the way from the moment it enters the
logic board until the video board (attached to the neck of the CRT).
The signal is there (it has different shapes but it is 18KHz). The
output of both transistors is 18KHz and so is the output of the
transformer. I traced it across resistors and capacitors as well. The
voltage (Vpp) does change as expected but the signal is present. Pin 6
and 7 have the 18KHz signal too on the CRT connector. However they
only measure 7 and 10V respectively.
Regards,
Vlad.
On 31 August 2015 at 02:26, tony duell <ard at p850ug1.demon.co.uk> wrote:
Hi Tony,
I have checked the horizontal signal from the MDA using an
oscilloscope. It is pin 8 like you mentioned. I get a regular 18KHz or
so signal out of that. Pin 9 gives the vertical signal at roughly
50Hz.
OK. Your PC and MDA card seem to be OK.
Now trace through the horizontail circuit in the 5151. IIRC there
is a driver transistor, the collector load of which is a transformer
which couples to the base of the horizontal output transistor
(sorry, I am doing this from memory, I don't have the techref
in front of me). Do you get the 18kHz on the collector of
the driver transistor?
Are both transistors good?
-tony
9:54 p.m.
Hi,
I traced the 18Khz signal all the way from the moment it enters the
logic board until the video board (attached to the neck of the CRT).
The signal is there (it has different shapes but it is 18KHz). The
No, that is a different 18kHz signal. That is the video, which will
have a significant component at the horizontal frequency. It
starts from pins 6 (intensity) and 7 (video) of the DE9 connector
You need to trace on from pin 8 to transistors on the main board,
right up to the flyback transformer.
-tony
1 Sep
1 Sep
6:57 a.m.
On 1 September 2015 at 00:54, tony duell <ard at p850ug1.demon.co.uk> wrote:
Oh, I think I understand now Video is different than horizontal board.
Hi,
I traced the 18Khz signal all the way from the moment it enters the
logic board until the video board (attached to the neck of the CRT).
The signal is there (it has different shapes but it is 18KHz). The
No, that is a different 18kHz signal. That is the video, which will
have a significant component at the horizontal frequency. It
starts from pins 6 (intensity) and 7 (video) of the DE9 connector
You need to trace on from pin 8 to transistors on the
main board,
right up to the flyback transformer.
I did. The 18KHz signal is present when it enters the board from the
wire, it is also present on the collector of the following 2
transistors (the TR21 and TR22 which are part of the brightness
limiter and horizontal driver respectively), also at the output of the
T501 transformer and at the collector of the TR23 transistor (which is
labeled as Horizontal out). I then traced at every pin until the
flyback transformer input (pin 4). According to the schematic and the
board it seems that is the signal path from the moment it enters the
logic board until it reaches the flyback transformer.
However the flyback transformer is definitely not outputting the
voltages it is supposed to, as the manual tells me to measure 56.8V at
the cathode of diode D504 which is basically connected to the output
pin 6 of the flyback transformer and I only measure few mV.
Could a winding of the FBT be burned somehow?
Regards,
Vlad.
-tony
7:59 a.m.
You need to
trace on from pin 8 to transistors on the main board,
right up to the flyback transformer.
I did. The 18KHz signal is present when it enters the board from the
wire, it is also present on the collector of the following 2
transistors (the TR21 and TR22 which are part of the brightness
limiter and horizontal driver respectively), also at the output of the
T501 transformer and at the collector of the TR23 transistor (which is
labeled as Horizontal out). I then traced at every pin until the
flyback transformer input (pin 4). According to the schematic and the
board it seems that is the signal path from the moment it enters the
logic board until it reaches the flyback transformer. However the flyback transformer is definitely not
outputting the
voltages it is supposed to, as the manual tells me to measure 56.8V at
the cathode of diode D504 which is basically connected to the output
pin 6 of the flyback transformer and I only measure few mV.
Could a winding of the FBT be burned somehow?
Could be, You have a schematic, the flyback windings should be very
low resistances. Check them with the ohmmeter.
-tony
10:56 a.m.
On 1 September 2015 at 10:59, tony duell <ard at p850ug1.demon.co.uk> wrote:
What do you see on the collector of TR23, which should be a small power
transitor (TO220 package I think). If it's working properly there would be some
very high voltage spikes (kV) there, but under these conditions probably not. What
is the average DC voltage there?
Hmm, you are right, I am not seeing any spikes in voltage there. On
the collector of the TR23 all I am getting as DC voltage is around
110mV. The oscilloscope tells me I am getting Vpp of about 4.4V with
Vmax at 2.6V and Vmin at -1.8V and an average of 105mV (which matches
what my multimeter tells me too).
That sounds too low doesn't it?
Could be, You have a schematic, the flyback windings should be very
low resistances. Check them with the ohmmeter.
I did measure the resistances across pins of the flyback transformer
on the same windings and I am getting (what I think are) good results:
1 or 2.2 Ohms (for the 2 windings left and right, not the upper one,
as I do not want to touch the high voltage stuff for now).
-tony
10:57 a.m.
Hmm, you are right, I am not seeing any spikes in voltage there. On
the collector of the TR23 all I am getting as DC voltage is around
110mV. The oscilloscope tells me I am getting Vpp of about 4.4V with
Vmax at 2.6V and Vmin at -1.8V and an average of 105mV (which matches
what my multimeter tells me too).
That sounds too low doesn't it?
That is far too low.
Firstly, there should be a 12V or so feed to one pin on the flyback primary
winding (the winding that links to the collector of TR23). Is that present and
correct? What about other components connected to that winding.
Are you sure TR23 is good. The horizontal output transistor in many monitors
often fails.
-tony
11:27 a.m.
On Sep 1, 2015, at 1:57 PM, tony duell <ard at p850ug1.demon.co.uk> wrote:
Yes it is. I am getting 15V on pin 4 that connects to the collector of TR23.
Hmm, you are right, I am not seeing any spikes in voltage there. On
the collector of the TR23 all I am getting as DC voltage is around
110mV. The oscilloscope tells me I am getting Vpp of about 4.4V with
Vmax at 2.6V and Vmin at -1.8V and an average of 105mV (which matches
what my multimeter tells me too).
That sounds too low doesn't it?
That is far too low.
Firstly, there should be a 12V or so feed to one pin on the flyback primary
winding (the winding that links to the collector of TR23). Is that present and
correct? What about other components connected to that winding.
There is a diode and a capacitor. They both measure 300mV or so. The diode seems to
be working. I will desolder one leg of the capacitor and check it too. I do not have an
ESR meter so I will do normal checking.
Are you sure TR23 is good. The horizontal output transistor in many monitors
often fails.
I am not sure. I assume I have to desolder it to check it right?
Regards,
Vlad
-tony
11:56 a.m.
Are you sure
TR23 is good. The horizontal output transistor in many monitors
often fails.
I am not sure. I assume I have to desolder it to check it right?
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18 comments
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ard＠p850ug1.demon.co.uk -
billdegnan＠gmail.com -
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vlad.stamate＠gmail.com