HP 437 Power meter

[Nemo1956]

Can anyone help me out. I have one of these units and now when I need to use it it goes tits up on me the next day i used it. It was working fine the day before.
It will see the power sensor but when I put it onto the 50MHz ref signal it will not read anything. I have looked at the ref output and that is fine. I have put the sensor onto my signal generator with no reading at all just seeing noise.I have also put my sensor onto others units and it works fine. I have even out the sensor from these other bit of kit on to it still the same but they all work.
Does anyone have a schematic for these so I can find the fault.
Thanks.
Paul.

 

[davenn]

It will see the power sensor but when I put it onto the 50MHz ref signal it will not read anything. I have looked at the ref output and that is fine. I have put the sensor onto my signal generator with no reading at all just seeing noise.I have also put my sensor onto others units and it works fine. I have even out the sensor from these other bit of kit on to it still the same but they all work.

the #1 probable cause is that you have killed the sensor head with excessive power ... they are a 10mW max

 

[Nemo1956]

I have tested the power senors on different units and they all work.
That the problem there must be a device that has given up on it.
So im asking for a schematic for it so I can see just what is going on here.
I have been looking on the inter web and found a service guide but no schematics attached.

 

[davenn]

So im asking for a schematic for it so I can see just what is going on here.
I have been looking on the inter web and found a service guide but no schematics attached.

have you downloaded this one ?

https://elektrotanya.com/hp_437b_power-meter_sm.pdf/download.html

hmmmm doesn't seem to have a schematic

so to confirm which model you have 437A or 437B ?

 

[Nemo1956]

Yes I have that one and have been going over it but it does not lead to where the problem may be. But just states if this is not working change U25 or U26.
Mmmmmm. But it does not tell you any voltages that you should be able to see.
But thanks for you help.