Just in case someone else would like to save one of these old GPSs from
the trash, if it has the apparently blank LCD problem...

My unit had the symptom of no LCD display (like it was turned off), but
the unit properly beeps when powered on, and the POS LED properly
lights.

I found that the -5V LCD drive voltage had failed which causes the
contrast to be turned off. The -5V inverter is on the small daughter
PCB that is around the antenna connector on the lower main PCB.

Remove the battery cover.

Remove the battery cover gasket, then remove the 4 screws, then remove
the back GPS cover

Remove the top PCB (4 screws) and carefully unfold the ribbon cable.

Remove the lower PCB (4 screws) and pry the PCB out from the light
button side 1st, being careful not to mess up the button rubber pieces.

You will see a small daughter PCB under this PCB that surrounds the
antenna connector. This small PCB also has the beeper on it. Unplug
this PCB as this is the PCB with the -5V inverter on it.

Replace the two electrolytic SMT caps that are on either side (above
and below) of the 8 pin SOIC labeled "7600" which is a switching power
supply controller/inverter. I replaced the caps with SMT tantalums
(remember Tant polarity markings are opposite of the AL electrolytics).
Reassemble and test.

Regards to all who want to keep old stuff running :-) Craig

Could you provide details on how you tracked this down to these two caps?
Did you use a ESR meter and if so what one? Or was there some other method?
Thanks, it is kind of like that "teach a man to fish or give him a few fish
thing"
Russ
"cpu_nut" wrote in message
oups.com...
Just in case someone else would like to save one of these old GPSs from
the trash, if it has the apparently blank LCD problem...

My unit had the symptom of no LCD display (like it was turned off), but
the unit properly beeps when powered on, and the POS LED properly
lights.

I found that the -5V LCD drive voltage had failed which causes the
contrast to be turned off. The -5V inverter is on the small daughter
PCB that is around the antenna connector on the lower main PCB.

Remove the battery cover.

Remove the battery cover gasket, then remove the 4 screws, then remove
the back GPS cover

Remove the top PCB (4 screws) and carefully unfold the ribbon cable.

Remove the lower PCB (4 screws) and pry the PCB out from the light
button side 1st, being careful not to mess up the button rubber pieces.

You will see a small daughter PCB under this PCB that surrounds the
antenna connector. This small PCB also has the beeper on it. Unplug
this PCB as this is the PCB with the -5V inverter on it.

Replace the two electrolytic SMT caps that are on either side (above
and below) of the 8 pin SOIC labeled "7600" which is a switching power
supply controller/inverter. I replaced the caps with SMT tantalums
(remember Tant polarity markings are opposite of the AL electrolytics).
Reassemble and test.

Regards to all who want to keep old stuff running :-) Craig

Hi Russ, The first hopeful sign that the IPS-360 was not totally dead
(although the display was 100% blank) was that, upon switching on, the
beeper beeped and the POS LED came on. When I disconnected the GPS
antenna (with the power off), there were additional beeps (I assume an
error indication) when the switch was turned on, which I assumed was
also a good sign that the main microprocessor was running.

My first troubleshooting started with the LCD controller which is the
"Sharp 7930" on the back side of the PCB that the LCD crystal is on.
Search on "EN2778C.pdf" to get the data sheet. As of Nov 2005:
http://service.semic.sanyo.co.jp/semi/ds_e/EN2778C.pdf. I saw that the
various TTL (0 to 5V) clocks were running on the Sharp chip which is a
hopeful sign.

I then measured that the -5V was absent on pin 36 "Vee". All LCDs
require a negative voltage on the LCD crystal which is the voltage that
provides the contrast. Then I traced the -5V back to the small
daughter PCB through the ribbon cable, and the small connector to the
daughter (small) PCB.

On the daughter PCB, I recognised the inverter chip "7660" from
previous experience. I was familiar with the 8 pin inverter chip
"7660" and how it uses the capacitors (one is a charge pump, and the
other is the negative V filter) so I just knew that these were likely
causes of failure for aluminum electrolytic capacitors. The main issue
here is that Al electrolytic capacitors are often a weak point in a
design. With an O-scope I saw that the 7660 was oscillating (a
requirement for a charge pump to operate), but its output to the PCB
trace that went to the Sharp 7930 was at zero volts with just a bit
(maybe 0.1V) of the 7660's square wave from the oscillator. From
experience I knew the electrolytics were the most likely problem
especially since the 7660 itself was switching / oscillating. There is
also a small diode in the circuit around the 7660, and I verified that
it was good with a VOM / diode tester. I replaced both capacitors with
tantalum capacitors since I know that this type will last longer in
this circuit.

I think just about every IPS-360 has failed in this fashion from the
little that I have read online, and I hope this information will keep a
few alive for history.

I hope that helps, Craig