Electronics > Repair
Anritsu / Wiltron S331A - Service Manual / Schematic
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z1zmail:
Ciao, hai controllato la tensione al pin 4 del display ( V0)? È la regolazione del contrasto; se  è inferiore ai 10V, sembra spento.
vishaldotgupta:
 i am not sure if you still need any help.  but

1.  you need to make sure if the system is still booting. to do so, press on button and wait.  do you hear any beep sound?   does backlight switch works.  if yes, press contrast button and try to increase contrast. 

2.  if increasing contrast does not help,  make sure contrast voltage is present.  check LCD data sheet and check  pin no for for contrast voltage value.   if not in limit, the contrast driver could be faulty.

3.  if still not working, check if there is activity on data and clock lines of LCD.  if  it is there, then probably you LCD has gone bad.  if no activity, then system is no booting.

4.  remove PLCC EEPROM, clean contact with plug it back.  Try switching on again

hope it helps
vishaldotgupta:
the way S331 works is as follows.

The RF injected into the coupler bridge, two measurements are made.  one is called Reference and the other is Reflected.

When for some reason  reference is missing, sweep will be very slow.  and when Reflected cannot be detected, the VSWR will be 1.  and a flat line.

so in your case you need to probe the reflection measurement circuity right upto the A/D converter
vishaldotgupta:
this most likely is a RF diode.

just try touching its pins using a tweezer.

when you touch does the sweep speed increases and you get VSWR graph?  if yes, most likely it is faulty.  u need to also check the capacitor and resistance around it to be sure
rg58:
Thanks for all that effort, vishaldotgupta! All correct what you said.

However, unfortunately your reply was 11 months after my last post, so the unit is already long gone. Still not exactly sure what cause the sudden death while the unit was sitting quietly on my table. At the end I probed around and (if I remember correctly) I could trace it back to a faulty negative voltage supply for the display itself, but could not figure out the reason at that time. Something seemed wrong with one of the DC/DC converters.

As the unit was in an overall rather messy condition, I decided not to waste more precious hours on that one.
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