Re: Tempest - Nearly there but still some issues

hey if it helps u can power it up w/out "math box pokey" PCB
i use that to fix my dac and ram fualts Damm 5v reg going 7.5v
  ----- Original Message -----
  From: Colin Davies
  To: vectorlist@vectorlist.org
  Sent: Saturday, September 20, 2008 9:03 AM
  Subject: VECTOR: Tempest - Nearly there but still some issues

  Ok.... I still had some issues with this Tempest pcb... Its nearly there, but it wont run the game !!

  ## Repairs done ##
  ################

  I replaced the Program Ram last night, and this cured my 1st issue...
  I replaced a pair of the Vector Rams that were failing with the Fluke - 2000>23FF failed - Rest 2400>2fff was OK... This fixed this... Ram tests ok 2000>23FF

  Put into Diagnotic mode and ran unit under test ( I've also plugged in the cpu just to be sure).. I get a constant tone... as before, indicating that the vector rom might be bad....

  The Vector test was pulsing at this point, so I grabbed my scope... Nothing on the XY outputs, there is a size pot missing on X size, no worries, I'll back track...

  Looked at the section between each DAC output (the centering and inverting) and before it goes to the analogue multipliers for the correction... Found a good test point on the resistor that feeds each multiplier circuit... Found one of the TL082 op-amps was faulty... essentially killing the X output dead...replaced..... OK. but... X signal is unipolar, and not much detail, the Y signal is fine... replaced the X DAC, X is back...

  This now allowed me to look at the screen on the scope, although its hard to make out.... There are no rom errors but I had what looked like a Q... This indicates a problem with one of the pokeys... Replaced both to save time.... Letters are now gone and so is the constant tone !!

  So... This looks like its all nearly working now, the test screens pass, with no bad roms or other letters - I guess I would get an M if the mathbox was faulty (looking at the trouble shooting guide).... I still need to sort out the final XY output stage.....

  ## Current problem ###
  ###################

  It refuses to boot up into the game !!! - Looks like its just watchdogging ???.

  Now is this something very simple ?, I have no controls connected or coin door stuff ( In fact I have no controls at the moment at all !!)....Its just a loom, power brick, ARII and game pcb on the bench...

  Should it boot up into the game with the parts missing ? - I would guess that it should, but maybe I'm missing something .... Is it maybe looking for the output from the encoder ?

  Thanks, Regards, Colin

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Sat Sep 20 01:34:44 2008