WAVETEK 191 has a burnt out varistor

[chou560]

I bought this wavetek at a great price and before powering it up I look inside. I found the varistor "VR1" had burnt out severely and left a coat of black smoke film on the PCB and the back plate.

What could have caused it to burn this bad and what other components could have been affected by this.

I will clean the area first and look for any signs of over heating and damage before doing anything else'
I bought a new replacement for the varistor P/N V56ZA8.

What do you guys think. Your input is greatly appreciated.
I'm a new member here at this site and I'm glad I joined.
Thank you

 

[gmphadte]

First of all, you have to check what is the mains voltage specified and the voltage selected on the unit. If the unit was connected to higher voltage than specified e.g. 230volts with the selector at 110 volts, the varistor will blow. It will also blow if high voltage appeared due to some fault in the incoming mains.

Now that the varistor is blown, you have to check whether the fuse is also blown. Then set the voltage selector to your mains voltage.

Replace the faulty parts. Be sure to replace the fuse of the same type and rating, if needed.

Power it ON and be responsive to switch it off if any problem occurs.

Gajanan Phadte

 

[tauro0221]

Hi,
It can be from an over voltage, from aging or contamination.

 

[Bibliophile]

That varistor is designed to clamp at between 50 and 62 Volts.
Can you discern what part of the circuit it is protecting?

 

[gmphadte]

Get your service manual from the net.

Gajanan Phadte