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aleksazr
Joined: 26 Apr 2015 Posts: 9
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Posted: Sun Apr 26, 2015 7:27 am Post subject: Gateway VX1120 horizontal lines on top |
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Hi all, this is my first post here.
I was given (for free) a Gateway VX1120 CRT monitor a few years ago.
It had two problems, the color RED was missing at times and the whole
screen could go black. Those two I have fixed, even though I have very
little knowledge of electronics in general (by soldering bad joints).
But now I have a third problem, there are horizontal lines on top of the
screen, for which, as I have googled it, is responsible one capacitor,
his ESR has changed. Which one?
I've opened the monitor in hope the capacitor has changed his outer
appearance, but no luck... and my knowledge ends here
If someone knows which one it is, I'll take some pictures of the inside
of the monitor, so he/she can circle it on the pic. |
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torbjorn
Joined: 07 Jun 2007 Posts: 370 Location: Sweden
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Posted: Mon May 04, 2015 3:01 pm Post subject: |
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I dont know any exact details of just that monitor, but if you look at a typical vertical output stage built with bipolar transistors (usually within an IC), there is a so-called bootstrap capacitor, which serves to make sure that the "upper" transistor in the complementary output stage gets good base drive during the retrace. For instance, looking at a schematic with the old IC TDA1170S http://elcomp.ru/images/catalog/tos/tda1170s.gif , it is the 100 uF capacitor connected between pins 3 and 5.
I think you can easily locate that capacitor if you check out what IC is used for vertical deflection in your monitor, and then look in the datasheet for that IC.
For the sake of completeness, the same kind of error can be caused by the flyback diode (1N4001 connected between supply voltage and pin 5 in the TDA1170S schematic, sometimes integrated in more recent ICs), but that is more seldom. |
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aleksazr
Joined: 26 Apr 2015 Posts: 9
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Posted: Mon May 04, 2015 4:52 pm Post subject: |
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Thanks!
IIRC there are two ICs inside (that I saw):
one on the horizontal PCB on the bottom (DIP, around 40 pins),
and one on the back of the tube, a smaller, vertical PCB. (DIP, around 32 pins).
That is the one I have re-soldered to fix the black screen problem.
I'll open the monitor in a few days. |
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aleksazr
Joined: 26 Apr 2015 Posts: 9
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Posted: Tue May 05, 2015 7:50 am Post subject: |
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The DIP 32 is M52746SP
Could it be that one? The DIP40 IC is not easy to access... |
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torbjorn
Joined: 07 Jun 2007 Posts: 370 Location: Sweden
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Posted: Tue May 05, 2015 8:10 am Post subject: |
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No, i think the vertical output IC will be a single-in-line part with about 10 pins, mounted to a heat sink. Probably you will find it near the wiring to the deflection coils. |
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aleksazr
Joined: 26 Apr 2015 Posts: 9
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Posted: Tue May 05, 2015 8:13 am Post subject: |
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The DIP40 is actually DIP56 ST72771N9B which is a MCU.
There is also this one M35071
There is one more IC that I can't get to, yet. |
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aleksazr
Joined: 26 Apr 2015 Posts: 9
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Posted: Tue May 05, 2015 8:21 am Post subject: |
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torbjorn wrote: | No, i think the vertical output IC will be a single-in-line part with about 10 pins, mounted to a heat sink. Probably you will find it near the wiring to the deflection coils. |
This one?
http://www.ti.com/lit/ds/symlink/lm2402.pdf |
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torbjorn
Joined: 07 Jun 2007 Posts: 370 Location: Sweden
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Posted: Tue May 05, 2015 9:38 am Post subject: |
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No, none of these. I think it should be placed on the main PCB, not at the CRT socket. The casing is probably similar to that of the LM2402. |
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Tue May 05, 2015 10:18 am Post subject: |
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Possibly IC401(LA7841L) ? _________________ You're over there, I'm over here. |
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aleksazr
Joined: 26 Apr 2015 Posts: 9
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Posted: Tue May 05, 2015 11:48 am Post subject: |
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jts1957 wrote: | Possibly IC401(LA7841L) ? |
I've found IC401, but it is TDA9309 not LA7841L.
Is that the one? If so, is it between pins 3 and 5, or 3 and 6?
If it is, I'll have to unscrew every screw there is |
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