Resistor/Fuse replacement (DEC H7104-D)

Mattis Lind mattislind at
Wed Mar 23 03:40:56 CDT 2016

2016-03-22 20:47 GMT+01:00 Noel Chiappa <jnc at>:

>     > From: Josh Dersch
>     > I have no excuse, I just get nervous working on these things.
> I should hope you do get nervous! Anytime one is working around equipment
> that
> contains lethal voltages, one _should_ be nervous! It helps with...

Don't work with lethal voltages! Use a insulation transformer. Then it is
not as likely to kill you unless you brake the rule and put both your hands
in the supply. Then use a variac. My experience is that you can observe the
behaviour at a much lower voltage when the load is small. This supply if I
remember correctly will work fine from 60 VDC at the input caps.

I do this all the time. I am not nervous when putting the scope-probe on
anything in there.

One more thing regarding the H7104. The circuit that enables the relay will
also enable the signal to the main chopper transistors. Thus there will be
no switching at all unless the input voltage is above 250VDC or so. I
disabled this circuit for testing purposes. As long as the load is small
this should not cause any problems. (And since I tested I know it didn't)

>     > I suppose eventually I'll get used to it.
> Don't get too used to it, one wants to always be aware and cautious!
> (I myself am missing half a nail - and I'm lucky that's all that's missing
> -
> because I got too "used to" working with my table saw...)
>         Noel


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