Re: Sys 80 bootup issue

On Oct 8, 1:17 pm, "Dan Beck" <biscuitbecks@*nospam*cableone.net>
wrote:
"taylor34" <at93...@xxxxxxxxx> wrote in message

news:f0301893-9690-436f-9743-36e763990a75@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Oct 8, 2:11 am, "PistolPete" <bloc...@xxxxxxxxxxxxx> wrote:



"taylor34" <at93...@xxxxxxxxx> wrote in message

news:f410a2df-9974-4b9f-8ee0-4840c6ab11db@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Hello--

Working on a panthera sys 80 machine, have gotten past the power
supply and am now to the cpu board. The board itself is clean, so I
started going through clay's guide. The first part passes, I get 4.5
volts at pin 40 of U1 (I've replaced this chip btw). So I moved to
the 2nd part, trying to get a clock signal on pin 37 of U1. I checked
Z3, and I was getting clock signal on pins 1 to 5--however, pin 6 was
not. As a result, I replaced Z3--no change though in operation. My
next thought was to replace Z2, but before I do that, is there
something else I should be looking at as a culprit? Thanks!

Taylor34

Have you checked the traces, components and timing of the reset circuit
signal? My BH wouldn't boot. going through the normal order of operation
brought me to the reset circuit. Seemed it fired too quickly on my board,
before voltage truly stabilized and the CPU was ready. I swapped in a
different value capacitor to get the proper time-to-reset-pulse. and the
game has worked flawlessly ever since. Stacked tolerances in parts will
mean
failures every so often, even if all the original parts are "within spec"
when checked individually.

PistolPete
Baltimore, Maryland

** Posted fromhttp://www.teranews.com**

I believe that the reset stuff is working ok at least on my bench
since the board fires up there. Panthera doesn't have the extra reset
card so luckily I don't have to worry about that. I'll try and record
some voltages off of U1 tonight, see if that might shed some light on
what's going on. Z2 and Z3 appear to working even when in the
machine, I get clock signals on them--it appears that U1 isn't
starting for some reason (btw, I replaced the chip and put in a socket
for it, so the chip itself should be ok). Thanks

Taylor34

Hello,

have you investigated/replaced the 12 VDC filter cap and its associated
bridge rectifier, in the cabinet bottom? It may be the case that they are
tired, and need to be replaced; certainly the cap for sure, if it's orange!
:-)

I have no experience with the Rottendog power supply; I can't testify
for/against its use. My opinion is a properly rebuilt System 80 power
supply is more than adequate for a System 80 game...

When you have the board powered up on the bench, do you have the pulsing
data/address lines, and the pulsing IRQ lines? Hopefully you own a logic
probe for this... :-)

Regards,
Dan

I have replaced the cap down there, it wasn't orange but it didn't
look good. I would have used the original supply but it was missing
the heatsink and nobody around here had another one unfortunately, so
the rottendog was my only option.

I got some voltages tonight from some pins:
U1 pin 2 - 4.8volts, pin 40 - 4.6 volts, pin 39 4.7 volt, pin 37 4.8
volts, pin 4 0.2 volts.
U4, U5, U6 pin 37 - 4.8 volts

From looking at Clay's document, it looks like my IRQ line isn't
working when my voltage is lower (aka not on my bench). Looks like it
could be anything from a riot chip to z11 to z15, but since it's a
voltage issue that might narrow it down. Anyone have a similar
experience that might point to one or the other? Only one riot chip
on my board has been replaced before, U5, btw. Thanks!

Taylor34
.

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