[TechAssist] Re: Dell Ultrascan 20TX, 1997 19" computer monitor, low screen voltage, need schematic

From: Kevin <kevintv@xxxxxxx>
To: techassist@xxxxxxxxxxxxx
Date: Mon, 31 Jan 2005 15:55:41 -0800
G1 is -55 volts.  The cathodes are +55 volts.  

Kevin Wilks
Kevin's TV & Video Repair
Penticton BC Canada
kevintv@xxxxxxx 
 

-----Original Message-----
From: techassist-bounce@xxxxxxxxxxxxx
[mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Gary McCartney
Sent: Monday, January 31, 2005 3:37 PM
To: techassist@xxxxxxxxxxxxx
Subject: [TechAssist] Re: Dell Ultrascan 20TX, 1997 19" computer
monitor, low screen voltage, need schematic

Kevin, here are a few things I found regarding your monitor:

----------------------------------------------------------------------
Re: dell d2026t-hs (sony)bright screen then knicks off'

'"jeff" wrote:
 >bright screen with raster lines G2 measured 0v red, green and
 >blue drives
 >reads 10v. any ideas on this would be appreciated


I had a similar model with the same symptoms.


It was a bad LM1207N chip on the CRT socket board.


I have found that this problem is usually caused by the CXA1907S on the
same
board. The LM1207 has usually caused one of the three guns, usually
blue,
to be over driven and saturating the screen. This is usually intermitent
and can be temporarily stopped with freeze spray.
Good luck, Kevin Penney

-------------------------------------------------------------------

IC 420  (CXA1907S) is a common problem on this unit.
However, the usual symptom is dark image, missing color(s), etc.

For a bright-white screen you will have:
        Excess G2 (measure with 10k probe)
        High G1 voltage (s/b -10 to -90vdc)
        Shorted Cathodes (usually run in the range of 70-120vdc)

Not saying that the IC420 couldn't give your symptom, just not typical.
It's a fairly high-density DIP IC on the video PCB.
(We normally like to socket DIP IC's when replacing, but I have yet to 
find a socket for this IC!)

Regards..........Jim

  James D. Kocmoud
             KMR Technical Services, Inc.
        6727 W. Cermak Rd.   Berwyn, IL  USA 60402
        Phone: 708-788-9000   Fax: 708-788-9010
           Visit us at http://www.kmrtech.com
              E-Mail to: james@xxxxxxxxxxx
                Quality Service since 1990

------------------------------------------------------------------------







Gary McCartney

McCartney Electronics
Guelph Ontario Canada
Est. 1984
email: gary (at) number63.ca








Kevin wrote:
> There is no fan.  It is a Sony chassis with a Sony picture tube.  The
> model number is D2026T-HS.  G2 is definitely connected to the
> transistor, but does not go through the transistor to get to the CRT.
> The transistor checks good.  I want to change the resistor, but I
can't
> find one so far.  
> 
> Kevin Wilks
> Kevin's TV & Video Repair
> Penticton BC Canada
> kevintv@xxxxxxx 
>  
> 
> -----Original Message-----
> From: techassist-bounce@xxxxxxxxxxxxx
> [mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Gary McCartney
> Sent: Monday, January 31, 2005 2:23 PM
> To: techassist@xxxxxxxxxxxxx
> Subject: [TechAssist] Re: Dell Ultrascan 20TX, 1997 19" computer
> monitor, low screen voltage, need schematic
> 
> Kevin, is there a fan in the unit? If so the fan might be dead,
causing 
> the shutdown. Also, try changing that 2.2 meg resistor even though it 
> checks ok. I'm not really familiar with the circuit, but it sounds a
bit
> 
> strange that there is a transistor connected to the G2. Can you verify

> that? Is the transistor pulling the G2 down to 4V?
> 
> Are the any other model/ chassis numbers? It might be a Sony chassis.
> 
> 
> 
> 
> Gary McCartney
> 
> McCartney Electronics
> Guelph Ontario Canada
> Est. 1984
> email: gary (at) number63.ca
> 
> 
> 
> 
> 
> 
> 
> 
> Kevin wrote:
> 
>>This monitor comes on with HV, filaments, and no video for about 5
>>seconds and then it goes into shutdown with an amber light flashing.
>>The screen voltage or G2 measures only 4 volts and then drops to zero
>>when the monitor goes into shutdown.  I found 790 volts on one end of
>>R463 and 4 volts on the other end.  The 4 volt side is connected to G2
>>on the picture tube and to the collector of Q403, a C4686 transistor.
>>R463 measures correctly out of circuit at 2.2 meg ohms.  
>>
>>Kevin Wilks
>>Kevin's TV & Video Repair
>>Penticton BC Canada
>>kevintv@xxxxxxx 
>> 
>>
>>
>>
>>
> 
>
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References:
- [TechAssist] Re: Dell Ultrascan 20TX, 1997 19" computer monitor, low screen voltage, need schematic
  - From: Gary McCartney
[TechAssist] Re: Dell Ultrascan 20TX, 1997 19" computer monitor, low screen voltage, need schematic

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