varistor touble

[Enzo]

Oh, no argument about the thermal fuse, I have bypassed my share of them too.


A lot of high powered amps used a big traic as a power switch, and the switch in the control panel just runs that triac. This reduces the stress to the contacts in the power switch. An example of turn-on stress. A series thermistor softens the initial current surge to an amp. It thus reduces the tendency of power switch contacts from arcing, it reduces stress to the inner leads of the big filter caps, it reduces initial current surge through the power supply rectifiers. And so on. Is it necessary? Maybe not, but it does add to the overall reliability of a product.

If you can;t see the schematic, it is a simple circuit. Just imagine any amp mains circuit. Now add a 10 ohm resistor in series with the fuse. But it is a special 10 ohm resistor that turns itself into a .1 ohm resistor after a few seconds.

[ballzdeep]

Thank you everybody for your help. Still have not fired it up, the cord i used for my light bulb limiter was bad.(f'n Murphy)
I was going over the connections and noticed leads from power trans are not on correct terminals per the schem. Also noticed the schematic shows multiple leads going to the same tab. i know some of these connections will end up on the same block but have not sorted out yet what leads go to what components.

My next question however is does anyone have a easy way to test the tranny without powering up or what sort of resistance i should read across windings ( i have been told i should get at least 30 ohms across primary but that guy was sort of a mouth breather so i could use an experienced opinion) i always thought it would read very low like a short.

[Enzo]

That's what fuses are for. And a variac if you have one.

Resistance readings are pointless. WHo says the primary should read over 30 ohms? Maybe a specific transformer for a specific model of some amp, but not as some general rule. Resistance is a reflection of wire thickness, while transformers operate on turns ratios. SO you could pick up two differnt 12v transformers for example, and see totally different primary resistance because one was wound with heavier wire.

You wanna check out a transformer? RG has a swell little short detector you can make in minutes on his Geofex site.

But just you and a meter? Check that no winding is open. Check no winding is shorted to another. Check that no winding shorts to the frame.

After that, connect mains voltage to a primary winding though a fused mains source and see what happens. If it blows the fuse, it is bad. If it gets real hot, it is bad. If it doesn;t make voltage it is bad. If it draws a bunch of current it is bad.

[ballzdeep]

That was my argument exactly. Thanks for the confirmation and tips.
You are awesome Enzo.
i am sure everyone has met that guy who says idiotic things like that, same kind of people that watch game shows all day cause it reminds them of what is left of their education.
out of fuses and short on luck i will keep plugging @ it