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44 lines
3.4 KiB
44 lines
3.4 KiB
\documentclass[11pt]{article}
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%Gummi|065|=)
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\usepackage{graphicx}
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\usepackage{caption}
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\title{\textbf{Sony PVM 14M4U Repair}}
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\author{Steak Electronics}
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\date{}
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\begin{document}
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\maketitle
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\includegraphics[scale=0.3]{../pics/DSCN1101.JPG}
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\captionof{figure}{Barely User Service-able!}
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\section{Start}
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Video 1105.webm shows the problem. Lines moving both vertically (obvious) and horizontally (less obvious, looks diagnolly).
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The second problem, which was more of a problem at the start, was disassembly, and then putting it in a way that it could be repaired. Video from botnet Sony PVM-8041Q Monitor Teardown and Repair-iyJDam0blYA) Shows a repair of a smaller 10 inch model, and you can see, the user is able to easily access parts of the board to repair. However, the 14 inch models are not nearly as simple to access. The board with all the processing on it (the A board), is on the bottom of the chassis, and to take that out... well video 1104.webm shows what I had to do to get access to the board, while it's powered on.
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\section{CAUTION}
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The tube is extremely damgerous, and I get nervous anytime I go near it. Do NOT try this if you aren't careful. There is also 600V rails on the bottom of board A where the hi voltage (read flyback) transformer is. The only thing in our favor, is that there IS a service manual with some explanations of where everything is. The problem, as I already mentioned, is that actually servicing this device is near impossible.
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\section{Repair}
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At first I suspected capacitors had gone bad - due to the failure mode. When it originally failed, it had been working, then suddenly failed. I used an ESR meter but was unable to find any bad caps. This ESR meter is untested, so it's either that there are no bad caps, the bad caps have failed in a way besides high ESR, or that the esr meter doesn't actually work.
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I poked around a bit, but after a few minutes, remembered that voltages should always be checked somewhere early in the repair. Lucky for me, a -15v voltage is showing -25 volts. It being a negative voltage (in my limited knowledge) points to it being for an op amp, and op amps that don't have the right voltage might fail the H and V sync. I will try to fix that and hope there is no other damage.
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\includegraphics[scale=0.3]{../pics/DSCN1106.JPG}
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\captionof{figure}{The Rail is listed as -15V...}
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\includegraphics[scale=0.3]{../pics/DSCN1107.JPG}
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\captionof{figure}{Fault!}
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I looked around, and the output from the PWM is fed into a transformer, where it's rectified into a number of different voltages. The service manual tells all of this.
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\includegraphics[scale=0.6]{../pics/powerboardschematicblockdiagram.jpg}
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\captionof{figure}{PWM to Transformer to Zener}
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It appears that the -15V rail (as well as the +7V rail) both have rectifiers that keep voltage at a steady level. \footnote{Funny how zeners are universally considered "rookie" when I was starting electronics, and here is Sony in 1997 with state of the art televisions putting a zener in...} If there is 7 Volts on the one rail, and -25 on the other, I know that the zener must be the source of the error. There is a ceramic (I think) and a rubycon electrolytic, which is unlikely to have failed. I have not tested it for high ESR yet. The replacement diode they recommend however, doesn't appear to be a zener. It is either an EGP20G or an RGP15G diode. Both of these appear to be standard diodes. I'm not sure why this is.
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\end{document}
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