Emax

I got this Emax keyboard.

I recapped it, except for the two 250V caps.

I use it for a week, then the power supply breaks.

The PSU just ticks, the display flashes on and off and the floppy drive turns on and off.

It sounds like the PSU isn't rectifying the AC properly.

I immediately disconnected all the pcb's from the PSU board so as not to damage my machine.

The ticking turns out to be arcing electricity between the two pins on the pcb that come from the on/off switch. You can see it flashing.

I tested the bridge rectifier which tests ok.

I was going to get a new Thyristor and Schottky Rectifier.

Now, I'm hoping it's not the transformer that is knackered.

Any in-circuit tests I can do on the transformer?

Cheers for any help.

jim

Replace the ON/OFF Switch- it’s likely faulty. Both the neutral and hot go through the switch. If one side or the other is going out, then it would be reconnecting and disconnecting the AC - that’s what I would try first.

-T

On Mar 18, 2016, at 10:47 AM, jimshoppin@... [emax] <emax@yahoogroups.com> wrote:


I got this Emax keyboard.

I recapped it, except for the two 250V caps.

I use it for a week, then the power supply breaks.

The PSU just ticks, the display flashes on and off and the floppy drive turns on and off.

It sounds like the PSU isn't rectifying the AC properly.

I immediately disconnected all the pcb's from the PSU board so as not to damage my machine.

The ticking turns out to be arcing electricity between the two pins on the pcb that come from the on/off switch. You can see it flashing.

I tested the bridge rectifier which tests ok.

I was going to get a new Thyristor and Schottky Rectifier.

Now, I'm hoping it's not the transformer that is knackered.

Any in-circuit tests I can do on the transformer?

Cheers for any help.

jim








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