I just picked up a Tek 475, and it's got an interesting issue. After being on for about a minute, HV kicks off then cycles back on all by itself repeatedly. I've been poking around in the circuit, and I can't see anything that would cause it to cycle like this. The regulation circuit is working correctly and the HV is fine when it's on, but for some reason it kicks off. Anyone have any idea what may be causing it? All the waveforms and voltages in the manual check out, it's like it's switching itself off and then back on for no reason.

If it is solid state and the fluctuations are slow then it may have a fail safe circuit to prevent over heating that is either detecting a real over-heat or has become too sensitive and is interperiting normal opperating temp (after HV warm up) as over heat. I'm not familiar with this model (as is the case for most good test equip) so all I can offer is speculation.

Hope this helps.

Tom C.

There is no overheating protection, just overvoltage and regulation. I'm beginning to think the driver transistor is messed up, it's like a switch somewhere is being flipped off briefly then back on. Causes the lights on the front to go out too, strange.

Have you tried the TekScopes group on Yahoo... several discussions about 475 HV problems... just search.

http://tech.groups.yahoo.com/group/TekScopes/?yguid=201326600

jr

Still waiting for my registration to get activated.