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Subject: Re: [chromapolaris] Re: Chroma Polaris Lights up

From: Bob Grieb <bobgrieb@...>
Date: 2014-04-23

Hi Steve,

   Once you get your scope going, I would check the reset to the CPU, and also the
main clock input.   Also make sure that the power rails to the CPU and nearby chips
look good.  I usually check the chip select to the first EPROM (which may not be the
active one, but you can hunt around and try to find one that is getting hit).   Then look
at the data bus bits to the EPROM and RAM chips to see if one is stuck high or low.
I worked on a Polaris recently that had a bad microprocessor chip.  One of the signals coming out of the chip was sitting at an intermediate level, instead of switching high and low.   Luckily the owner of the Polaris had a spare board that we could take another CPU from.  Another thing to try is removing the CPU from its socket and then putting it back.  You could also wipe the socket contacts off with a Qtip and some IPA, but that may not be nec.  You would want to handle the CPU very carefully to avoid ESD damage to it.   Ideally you would not touch any of the pins, just the package, which usually means using tweezers to grab it.  Same idea as unplugging and plugging cables and socketed chips to clean the contacts off.  Maybe better to leave the CPU alone until you have reason to suspect it.

    Good luck with your troubleshooting.

             Bob


From: merolasteve <no_reply@yahoogroups.com>
To: chromapolaris@yahoogroups.com
Sent: Tuesday, April 22, 2014 12:37 PM
Subject: [chromapolaris] Re: Chroma Polaris Lights up, but makes no sound.



Just to follow-up.  I re-seated just about every cable.  I still need to re-seat the cables that connect to the panel PCBs.  I VERY carefully reseated the 2 flat foil cables on the right.  I might try and do the wire repair to the cracked far right cable while I save up some cash for new membranes.  So far the biggest mistake I made was not removing the batteries while reseating the RAM chips.  According to Paul it may or may not have damaged them.  No changes to the current problem is visible though.

My main problem seems to be that the computer has crashed.

I contacted Paul off list and asked a few questions while inquiring about the membranes.  I wanted to post some of it here so that in the future newbs like myself can see it when they buy non-working boards.  However, I am in this to learn as much as possible.  A lot of it comes from the Service Manual.

Things to test first:

-re-seat all cables
-re-seat chips, without the batteries installed and after caps are drained (I read this elsewhere)
-measure output voltages: +5V REF and + 5 DIG are adjustable and should be adjusted within about 1%; +12V ANA, -12V ANA, -5V should be within 5%
-measure AC OK (about 5V) and DC OK (at least 2.5V)
-for the above tests all cables should be connected and power should be on; for a ground connection, attach meter to ground lug sticking up near where the power cables plug into the main board.
-measure power supply ripple at 60Hz and 120Hz using a scope to see if there is significant ripple...I'm still learning about this one.
-refer to schematics for other locations to test power supply voltages

I have been too busy with my home-remodeling to do most of this, but will hopefuly get to it soon.  I ordered some leads for my scope and some DN5 DeOxit.