Electronics > Repair

Anritsu / Wiltron S331A - Service Manual / Schematic

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rg58:
Hi there,

I was lucky to get hold of one of these Anritsu S331A analyzers, but this one has at least 2 faults.

1) Unresponsive to key press, sometimes beeps (only the ON button always works to turn it ON, but not OFF)
2) Integrator Error during self-test (it shows SWR of 1.0 even nothing is connected to the antenna port)

Funny thing is, trying to turn it off (ON/OFF button), it produces vertical lines in the graph while scanning AND seems to move the "cursor" one step forward during scanning. All this is pretty weird. I already cleaned the keypad rubber which measures good (<200 Ohm), also the keys get about 5V on the PCB.

Does anyone have a Service Manual maybe? Or could share some advice repairing this?

metrologist:
Many times the integrator failure is due to burned input circuit.

The other issues sound like connectors.

https://dl.cdn-anritsu.com/en-us/test-measurement/files/Manuals/Maintenance-Manual/10580-00008.pdf

rg58:
Thanks, I will have a look at the input circuit (what I already suspected anyway, but was not eager to touch it before knowing more).

Regarding the keys, I think you need to press them really hard to make them work. What would be a normal resistance of the black conductive rubber pads that press on the copper traces on the PCB? I measured around 150-200 Ohms for all of them. Isn't it possible the property of the conductive rubber is changing over time, and the resistance should be much lower?

rg58:
Anyone knowing what this part is? Could that be a package of 4 RF diodes for the SWR bridge? It is connected to 51 ohm resistors as well as 1kOhm resistors.

During frequency sweep, SWR shows always 1 (with real antenna connected, or with open end anyways), so there is no (reflected) signal being measured at the bridge or input section. There *is* an RF signal coming out, however, it also looks quite small, well below 0dBm (<1mW).

Error message shown was "Integrator Error".

Would it be safe to measure this sensitive part with a multimeter on diode test?

metrologist:
What's the board #? It's likely a 3-xxxxx number.

You would use an RF probe and SPA to trace the signal.

The burned boards I've seen have the PCB charred where you see that bodge. That's because the telcom gorillas forget to turn off their PAs before connecting.

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