Rasterlist Archives: RE: How does this sound as a group project?

From: Paul Sommers <Paul.Sommers_at_cwo.com.au>
Date: Wed May 17 2000 - 18:40:25 EDT

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<TITLE>RE: RASTER: How does this sound as a group project??? (Longish)</TITLE>
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Mike,

That's great. Thanks for contributing!

Yes your ramblings have proved to be very successful in helping me understand and fix Williams boardset. Using your material I'm actually quite good at it and getting better every day (although I have a Defender problem which is proving a headache - but I'll look at it again next week)

Cheers
 Paul

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 From:   mike_ranger@dofasco.ca
 Reply To:       rasterlist@synthcom.com
 Sent:   Wednesday, 17 May 2000 22:58
 To:     rasterlist@synthcom.com
 Cc:     Paul.Tonizzo@sybase.com; TonyBerry@dameon.net
 Subject:        RE: RASTER: How does this sound as a group project??? (Longish)

> Last night someone dropped off a Stargate boardset for me to have a go a
 > repairing. As I don't really know what I'm doing I always set their
 > expectations that they may get it back still broken.
 > 
 > I sat down with the info from Dave Langley's website (in particular The
 > Ranger Chronicles) and within an hour had fixed the boardset.
 > 
         [Ranger Mike]  
         Tee Hee!  Kudos go to Stef and Dave for saving and displaying some
 madman's ramblings!  Glad they helped somewhat!

As far as general repair guides go I will discuss a bench set up,
 leaving cabinet wireing out of it.  As always power, reseating and reflowing
 connctors are assumed before we get into the chip level repairs.

Pre repair:  Inspect the board.  I mean really inspect the board.
 Look at it for a while.  I picked up a dead space dual board cheap, and on
 pre-inspection found a small solder splat on the traces.  Peeled it off and
 the board worked!

here is what we are looking at:
         1) missing parts, backward parts, corrosion on chips.  Signs of
 arching (had this on my blaster set)
         2) damaged traces, long pins bent over shorting traces out. 
         3) Previous repairs.  Typically these can break traces under the
 socket or the chip that was fixed.  I would like to find the guy who keeps
 on using a curling iron as a soldering iron, cause I think I've repaired may
 boards he has looked at.

As far as general repair guides go, I can only speak of williams and
 PAC's since those are the only two I work on.  When I get a dead board to
 work on, I first hook it up and read the "Signs of life".  Let's say the
 board has no video output.  Power is good, and roms are all checksummes
 (Although I don't usually do this right off the bat, I tend to have a known
 good set of roms to use, easy given I limit the style of boards I repair)

1) Check to see that the CPU has a clock.  If not, fix it.
         2) I need some video output to give me hints, so I trace back from
 sync and fix that if it is missing or bad.
         3) Check and attempt to fix RGB signals, not always possible if the
 ram is not being strobed properly.

Now I have a board giving me some video clues.  I now want the self
 test's to run, so I can replace any faulty ram.

4) To get the self test to run, I start looking around the CPU.
 Clock signal must be present, IRQ must not be held in the wrong state for
 that CPU, halt must be okay, and rest must not be toggling.  Fixes for IRQ
 and halt are generally simple, but reset (watchdog) can be more difficult.
 It always helps to have a known good CPU chip as well.  I like to keep a
 spare working board of the style I repair so I can test chips in it, or
 borrow known working ones from it.

5) If watchdog is Toggling, I trace it back, and 50% of the time, I
 find a fault in the watchdog circuitry.  7474 or counter problems.
 74LS161's are my nemisis in these cases.  Bad sockets under the ROMs or the
 ROMS's themselves can be an issue here.

6) Once watchdog has settled down, (not gone away) I can generally
 see self test's run and point to bad ram.  I try Known good ram, and if the
 problems persist, I hit the write enables and any select, decoding
 circuitry, noting that some elements are used to get ram data to the bus,
 and that is important, and other circuits get it to the screen.

7) Fixed those up, and the game will generally run.  Poor graphics
 during attract means we have to look at the circuits responsible for getting
 data out to the screen, cause the CPU is not wachdogging anymore, so the bus
 data is fine.  Sometimes this can be separate ram/roms, sometimes it is
 shared.

8) then I look at CP inputs, to ensure thay are okay, and the last
 tidbit is the sound.  Sound is fairly unique between systems, so you are on
 your own.   The only hint there is to do the finger test.  Put your finger
 on the underside of the amplifier and if you get a hum, you have a good amp.
 If not, look at the amp as the issue.  This is one of the few places a scope
 comes in handy, but sound circuites are simple enought that it is not
 absolutley needed.

On the outside chance you are dealing with a bus problem
 (tranceivers, buffers) you will have an extremely tough time, as well as an
 intermitant trace. Sometimes I get lucky on this style of problem, sometimes
 I just want to snap the board in half across my knee, or sell it to Rick :-)

Thats all for now

Mike
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Received on Wed May 17 17:35:31 2000

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RE: How does this sound as a group project??? (Longish)