Furman PL-8 Series II

[lowell]

This power conditioner's circuit breaker keeps shutting the unit down. I have only plugged a light bulb into the unit at this point and the circuit breaker enacts. I measured current through the circuit breaker and it's only 4ma at most w/ the light bulb, at which point it still shuts off. Oh if I just leave the unit on w/ ANYTHING plugged in this happens, then in about 6 seconds it turns back on, the off again in about 3 seconds and continues this cycle. I have resoldered the whole board in a simple fix attempt. I'm not familiar w/ this circuit and cannot locate a schem online. If someone has any advice and/or a schem that'd be great.

[Enzo]

Did you contact Furman and ASK for a schematic?

At 120v, 4ma would be about a half watt. Is your light bulb a half watt bulb?

A breaking down MOV could do this.

[lowell]

Hi Enzo I emailed Furman for a schem. I see 2 MOVs in this. If you have a minute let me know what the purpose of these are and how a failing one might cause such an issue.

[Enzo]

A MOV is a surge limiter. It is sorta like a zener in that it doesn;t normally conduct until a certain voltage is reached. They come in various voltages. They often are wired across the mains and for example might have a 130v rating. SO any mains transient peaks over 130v will be shunted. That keeps the transients out of the equipment.

It is a varistor - Metal Oxide Varistor

(OK< The AC mains voltage is 120vRMS, but that means peak voltage is about 170V, so a 130v MOV would really shunt at whatever that peak voltage would be. See a data sheet)

After absorbing these peaks, they can become damaged and break down. Just like a zener can get leaky. I have no experience with your unit, but if it has MOVs in it, they can get leaky and even pop breakers.

The thing reliably fails, right? I mean you can plug it in and it definitely will crap out, right? Disconnect one end of each MOV and try the thing. if it no longer blows the breaker, then I'd say you found the trouble. If it makes no difference, then the MOVs are not it.

[lowell]

Furman will not supply me w/ a schem. right on thanks for that. one more quick question: so are movs only used for AC surges? Oh and I will try your suggestion, however I also see a little internal pot in the amp labeled "trip point." ??

[Enzo]

Trip point? SOunds like more involved circuitry inside than just surge suppression. I don;t know what that is.

[lowell]

ok right on. I pulled the MOV with no positive result.