> > 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?
Yes, but it's only 3 connections to desolder.
Obviously if the 2 junctions don't test properly as diodes, or if the Hfe is
much lo
On Sep 1, 2015, at 1:57 PM, tony duell wrote:
>>
>> 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 -1.8
>
> 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 multi
On 1 September 2015 at 10:59, tony duell 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
> > 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 o
On 1 September 2015 at 00:54, tony duell wrote:
>
>> 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 differe
> 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 sig
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 a
> 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 horizontai
> > 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 d
> 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 re
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 yo
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 th
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