Re: TECH:Rottendog Data East Power Supply DPS004 + older DMD

On Mar 13, 1:38 pm, donw <dweingar...@xxxxxxxxxxxxxxxx> wrote:
On Mar 12, 9:36 pm, "GPE" <GPE_NoS...@xxxxxxx> wrote:





"chuck" <ch...@xxxxxxxxxxx> wrote in message

news:b5382c36-ae0b-4be7-a2f0-44c2d6d59fa4@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I picked up a GnR pin with a rottendog power supply board and a non-
working dmd.  The power supply board had a blown zener diode and lm317
in the 68 volt section.  I replaced the diode with one Jim sent me.  I
put the DMD in another machine and it worked fine.  I tested the power
output and while not spot on it was close. Fuse blows, diode blows,
lm317 blows.  Replaced everything again.  Double check everything, the
smell of burning electronics again.  Ok, I'm not going to blow a third
set of components.  Check everything again.  All seems to be working.
Decided to consult with Don (pb2k team) and he suggested I check the
ohms on the display.  Sure enough 68v to ground was 38 ohms which drew
too much current and blew the section.

It seems the original wms board is current limted and Rottendog's
board is not.  Where this really comes into play is with older
displays that may be on their last leg.  Be careful when using this
power suppy with any older display.  A new display should work just
fine with it.

LM317AHV is rated 1.5amp. Your display was trying to draw (68/38) or nearly
1.8 amps.  Yep, I can see why the LM317AHV was having problems.  But, the
LM317AHV *IS* internally current limited and will shut itself down with
excessive current draw.  There is another problem with the LM317AHV design
that has been mentioned previously.  What you are seeing is EXACTLY the type
of failure that was mentioned in prior posts  ... but to stay out of an
arguement, I won't get into this.

- Ed- Hide quoted text -

- Show quoted text -

For whatever reason, the display was causing a load of 5 ohms on the
output of the LM317.  ON power up, the LM317 would be in current
limit.  The voltage on the output of the LM317 will be 1.5 volts.  The
voltage across the LM317 will be 100*1.414 - 44 - .7 -1.5 = 95volts.
The datasheets max voltage is 60 volts.  Goodbye LM317!

Replacing one of the zener diodes with a current limiting power
resistor would protect this circuit in cases where the display is
dying.- Hide quoted text -

- Show quoted text -

I have a similar issue with a R&B but with a brand new DMD.
I'm on my second set of diodes and resistors, but the LM317 seems to
be ok.
It starts off with flickering DMD during high use modes like tri-ball,
then eventually just stops working.

Quote: "Sure enough 68v to ground was 38 ohms which drew too much
current and blew the section."
How can I check this for my DMD?

.

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