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

[Jay Walling]

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 http://www.commusa.com/catalog.aspx/Motorola_CP200 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
[email protected]
Comark Corporation
93 West St.
Medfield, MA 02052
http://www.comarkcorp.com

 

[legg]

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 http://www.commusa.com/catalog.aspx/Motorola_CP200 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*

So sign the NDA and fix the problem with the frs assistance.

Signing an NDA is not the problem.

RL

 

[Harmonitron]

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
http://opilased.rvg.edu.ee/riistvar...oad=LCD_monitor_Hitachi_CML-176SXW_manual.pdf.
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
http://www.fixitwiki.com/index.php?title=HP1702_LCD_monitor_repair for
details.

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

 

[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
http://www.fixitwiki.com/index.php?title=OZ960_LCD_backlight_inverter_control_problems
for a typical OZ960 schematic.

 

[JW]

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
http://www.fixitwiki.com/index.php?title=OZ960_LCD_backlight_inverter_control_problems
for a typical OZ960 schematic.

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
http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0110S0100BLM21P.pdf)from
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.

 

[stefanosilva]

Looking for OZ960S

I'm looking for one oz960s, someone know where I can find It??
Many thanks for any help !!