Thanks again for your replies.

As this is the first PET I have ever owned, I'm not sure what the  
differences are between the variants. The product # on my motherboard  
says: 320081.

I had only a few moments this morning to do some quick probing around,  
and this is what I found.
all four 7805's basically have 0 volts going in or out. So I tested  
the voltages between GND and at the two IN5402 diodes (CR1 and CR2 on  
the 320081-2 schematic). I have 8.4V going into both and less than a  
volt coming out!

Phil



On Aug 9, 2009, at 4:32 AM, Ethan Dicks wrote:

> 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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