Viewsonic G73fm - completely dead

Hi, I've got a Viewsonic G73fm here that's absolutely dead - no response to power button, power LED is off, no sign of current draw (usually you get a little 'crack' if you plug a powered IEC into the back).

Does anyone have a service manual or schematic for this beast? Even a "The screws are hidden here and the case latches here" type diagram would be useful. The screws are obvious, it's the ones hidden under covers, and the plastic latches I'm worried about...

Failing that, I'd appreciate some suggestions of things I could check - I've done a bit of VCR repair but this is the first CRT I've tried to repair that might actually be repairable.

Thanks, Phil. snipped-for-privacy@despammed.com (valid address, but replace "despammed" with "dsl.pipex" to bypass spam filter)

Reply to
Philip Pemberton
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As bad as it is to reply to one's own emails, I've done some testing and found: - The AC inlet fuse (2.5A 20mm ceramic cartridge fuse) is blown. And by blown I mean completely open - infinite ohms. I can't use the "is the fuse melted (soft blow) or metal coated inside (severe overload)" trick because it's a ceramic-body fuse...

- All the rectifier diodes in the PSU section appear to be functional -

0.5V forward drop, "infinite" reverse drop, according to my DMM.

- The thing is absolutely full of "Luxon" electrolytic capacitors. Best guess about 20 of them. That and the fact this thing has an mfg date of 2001 puts it square in the "counterfeit capacitors" time frame and makes me bloody suspicious. No signs of cap leakage or bulging caps, but I'm still suspicious.

- The case is really easy to open up. No latches or hidden screws at all. Put the CRT face down on a towel (unless you WANT to scratch the CRT that is), remove all the screws on the back (4 around the front edge + 3 on the back panel) and lift the back away from the front section, shaking it gently if it gets stuck. Reassembly is just as easy - put the cover back on, then refit the screws.

- All the PCBs are marked with a logo that looks like "JEAN" - i.e. these guys: . So 99.9% chance it's a Viewsonic rebrand of a JEAN monitor. Why am I not surprised? Service info appears to be available, but only to those with a username and password, and no hint on how to apply for access. Yay.

I've found a few of the part numbers too: Monitor P/N: VCDTS22475-1E CRT: Chunghwa M41AJR53X76 / CP5440BNAC1S-TC / No. B 1163581016 Mainboard: G73FM 2202116700 VER:1.06 2001.04.20 Audio riser card: 2202117200 Barcode sticker on mainboard: 7562-00191-01050-0.0-A15025

Thanks, Phil. snipped-for-privacy@despammed.com (replace 'despammed' w/ 'dsl.pipex' to bypass spamtrap)

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Reply to
Philip Pemberton

Phil: Generally, the most common fault when the input fuse blows, is either a shorted rectifier diode (or Bridge) or the switching FET (on the heat sink) is shorted. Shorts on the output side of the switching power normally cause the power supply to shut down when it starts drawing too much current. I would direct my time to checking the parts on the primary side of the switching power supply. You might try checking the horizontal output transistor and some of the larger transistors and diodes in the secondary side if you cannot find the problem in the primary side. Hope this helps... John

Reply to
jdgill

Ah, the final chapter in the repair log.. :)

Buzzed out PSU with DMM from PSU side of fuse socket to N side of IEC inlet;

470KOhms, rising to a few megohms after a few seconds.

Replaced mains inlet fuse (2.5A 20mm antisurge/slow-blow) this morning, powered on to full white screen with no retrace lines. Connected VGA tester, loud "thunk" sound, followed by black screen and good image. Closed cover, put back into service this afternoon.

Total cost: a 20p fuse. Some repair...

--
Phil.
Reply to
Philip Pemberton

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