> Here is the story. Turned on my MLA-2500 and plate V. was 1600 volts.
>Found (3) shorted diodes in HV string. Replaced ALL diodes w/new ones.
>Turned it back on. Still 1600 Volts. Checked caps withe VOM and (1)
>looks open. New diodes held and still ck OK. Questions;
>
>1. Will one open cap in HV string drop HV from normal 2600 to 1600.
Someone please correct me if I am wrong, but I don't think the caps in
the HV string have anything to do with setting voltage. Aren't they
there along with the resistors for making sure the whole string of
rectifier diodes is balanced?
Also, please help me understand how you can check a cap with an Ohm
meter. Caps by characteristic are open circuits at DC. Do you have a
capacitance function on your meter? I know some of the newer ones do.
>
> Any thoughts on all of this is appreciated. BTW the HV xfmr looks OK
>best I can tell. Running it on 220vac and I ohmed it out. Amp tbl showed
>up at pwr up no load.
I suspect the transformer. The DC output of the supply is directly
related to the input. Caps help to filter out the ripple due to the
rectification and so may raise your RMS voltage a bit closer to the peak
DC voltage, but I don't think that it's a whole kilovolt as you are
seeing.
>
>Thanks in advance. Before I start spending money on new filter bank
>would appreciate your input.
My gut tells me it's not your filter bank. Perhaps one of the "new"
diodes you put in went bad, but perhaps your transformer is just not
properly working. I really suspect the transformer. Also, is your input
voltage really 230 Volts? You might want to check that.
If you have some form of HV probe and IF you are careful, measure the
output voltage from the transformer. Or, to be safer, you could put a
variac on the input of the transformer and measure the output with a low
input voltage. It looks like it's approximately a 10:1 transformer
ratio. So set your variac to 10 volts on the input and you should get
around 100 Volts on the output. That's a little safer than measuring
2600.
Hope this helps.
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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