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Inverter shutdown occurs on Dicon/Nextview 17" LCD monitor from 455MHz rf signal. Design flaw?

We seem to have run into a serious design flaw with the NV1740 LCD monitor. One of our customers has noticed (and we have re-produced the problem in our factory) that a 455MHz RF transmission from a Motorola CP200 handheld radio

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is knocking out the backlight on this monitor. The monitor must be power cycled before the inverter starts up again. I have poked around with an 'scope on the inverter, and know that the problem is localized to the inverter itself - the TFT controller does *not* drop the enable signal to the backlight. I suspect that the O2 micro OZ960 chip on the inverter is sensing an over-current situation on it's outputs and shutting down. I looked for a data sheet for the chip on O2 micro's website in the hope that I could adjust the over current sense circuit, but they do not offer them without an NDA. *sigh*

Shielding, grounding etc. have so far proved fruitless.

If anyone has a schematic of the NV1740 or the Inverter inside (A Frontek FIF1804), or even a datsheet/pinout for the oz960 inverter controller, (hell, even a schematic of *any* inverter with this chip) I would be extremely grateful.

Thank you.

[Remove MYBRAIN to reply by email]

Jay Walling Diagnostic Engineer snipped-for-privacy@MYBRAINcomarkcorp.com Comark Corporation

93 West St. Medfield, MA 02052
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Reply to
Jay Walling
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So sign the NDA and fix the problem with the frs assistance.

Signing an NDA is not the problem.

RL

Reply to
legg

OZ (O2micro) seem to be really holding their cards close to their chest. They don't seem to release data sheets for their chips!

The only schematic I could find on the web was a Hitachi service manual. See

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It has the chip pinout.

I had a similar problem with a HP1702 monitor. It would light for a second and then go dark. Sometimes it would stay on. See

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for details.

Jay, thanks very much for your details on your problem. It put me on the right track.

Reply to
Harmonitron

Jay, my repair didn't last.

I pulled down the OVP pin (2) to ground while I powered up the screen, held it for two seconds and let go. The backlight stayed on.

I added 1.5M in parallel with the 1M pull-down resistor on pin 2 and that seemed to work.

Every time I get the whole thing screwed together it fails again. It seems to be temperature dependent a bit though and will stay lit sometimes.

I presume the whole problem is due to changes in the tubes as they age. The designer hasn't quite got this figured out properly.

Anyone know what the correct thing to do is with the OVP signal? Should I use a capacitive divider since the lamp voltage is capacitively coupled?

See

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for a typical OZ960 schematic.

Reply to
Harmonitron

While I can't advise you how to fix your problem, I did finally manage to get a datasheet for the device, and fix the problem. I could email it to you if you give me your address, or post it to alt.binaries.schematics.electronic if you have proper usenet access, as you appear to be posting from a web based forum. The datasheet includes a reference design.

For the problem we were having with the 455KHz signal knocking out the inverters, I found that if we removed the capacitor connected to pin 18 of the OZ960 chip (thereby isolating it) and connected pin 18 to the removed cap and added a series ferrite bead (part # BLM21PG331SN1D from

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the cap to pin 6 of the chip, it fixed the problem. We have been reworking them for over a year now, and our customer is no longer having any problems with their displays.

Reply to
JW

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