On 8/8/09, B Degnan <billdeg@degnanco.com> wrote:
> Phil,
> What version of the PET 2001 do you have?  Is it a 2001-8 or a
> 2001-16/32N or a 2001-32B? I forget from the beginning of this thread.

My understanding is an 8K Static PET, based on the board number he
gave earlier.  That's what I've been using to shape my replies.

> If you have a later 2001 model, I found this comment in some notes I
> have "..check the voltages from the anodes of the diodes CR10,11,12
> located alongside the heatsink.  VR6 regulator supplies the -5V to the
> dynamic RAMs.

Later PETs do have a 7905 and I've tested the voltage at TP10.  The
PET of this thread has three 7805s in TO220 packages, not one 12V and
two 5V regulators in TO3 packages.  Different sections of this board
are driven by each regulator (I gave the grouping earlier).  You have
to check all three since they are not tied together.  If none are lit
up, and you know you have enough AC voltage coming out of the
transformer (8VAC ought to be enough), the next thing to check is the
rectifier diodes and maybe the large (though not as large as later
PETs) filter cap.

It's a simple linear power supply.  There are only about a dozen
elements to check, and half of them are only suspect if you have power
but it's bad power (too much ripple, noise, etc).  You can make a
really simple 5V PSU with just a source of about 8-9VAC, an
electrolytic cap for a filter, a small ceramic or tantalum as a bypass
cap for the 7805 and the 7805.  That's more-or-less what a static PET
has, but times three.

-ethan

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