Tempest repair log – auto firing logic issue

Status: FIXED

Repair cost:  $0.50

KLOV Posthttp://forums.arcade-museum.com/showthread.php?t=156908

Symptom:  Single shot firing doesn’t work.  Holding fire button down for auto-fire does work.

Diagnosis:  Since firing works, button is working.  Logic issue.


  • 10/30/2010 – Traced fire button back to 74LS157 @ D6 (Aux board).  Replaced chip and single shot firing now works.

Tempest repair log – AVG (main) board issue

Status: FIXED

Repair cost: $2 (questionable if part was really needed)

KLOV Posthttp://forums.arcade-museum.com/showthread.php?t=146427

Symptom:  Game board exhibiting strange display behavior – random vectors scrolling back and forth across screen.  Game plays blind.

Diagnosis:  Problem located on AVG board.


  • 08/21/2010 – AUX board and cable verified good.  Tested individual boards on a working setup.  Problem is located on AVG board.
  • 08/22/2010 – Cleaned and reseated 5 socketed RAMs, the 2 vector ROMs, and the CPU.  Board now has no XY output voltage.
  • 08/24/2010 – Tested several chips in the vector generator data shifter section, which confirmed good.  Logic probe pointed to DAC-312 @ D10.  Replaced with no change.
  • 10/30/2010 – Began with game in test mode, no display.  Swapped CPU with known working 6502 and got a single blue vector on screen and activity on the slam switch (switches test screens) and long steady beep.  Confirmed activity on CPU pin 37 & 39.  Activity on E2 pin 1 & 2.  Confirmed ROM activity on the CS1 & CS2 lines.  Theory of operation doc said long steady beep in test mode points to bad vector ROMs.  Flip-flopped the ROMs (socketed) and test pattern appeared.  Adjusting X/Y position, linearity and BIP controls brought test pattern into view.  Went out of test mode and game worked.

Notes: DAC replacement could have had an effect, but hard to tell since game was dead – DAC outputs never changed, but inputs upstream were still bad at that point.   However, after the DAC replacement, I never saw the pattern shown in the video again. Original CPU was later confirmed good.  Bad/dirty sockets ended up being the culprit despite cleaning of chip legs and using contact cleaner before they were inserted into their respective sockets.

Sanyo EZV-20 monitor repair log – HV shutdown

Status: FIXED

Repair cost: About $18

KLOV Post: http://forums.arcade-museum.com/showthread.php?p=1355615

Symptom:  Post-cap kit, monitor in HV shutdown, shakes, vertical collapse

Diagnosis: Voltage regulator bad?  Also could be B+ pot.


  • 7/23/2010 – After a cap kit, monitor went into HV shutdown shortly after being powered on.  B+ at 137v.
  • 9/24/2010 – Replaced Q901, IC601, VR601 (B+ pot).  Monitor now has the shakes (video). B+ sitting at 110-111v.
  • 2/6/2012 – Replaced TR402/TR403, monitor now has vertical collapse.
  • 2/12/2012 – VR354 is stuck at 18kOhm, and adjusting it does nothing, thinking pots might be bad?  Removed it, and once out, it tested good.
  • 3/3/2012 – Tested R473 (1 ohm, by the flyback) and it was bad. Replaced it with a 1/2 watt. R477 tested fine, but flaky, and looked pretty bad/burnt…easy decision to replace it.  3.3ohm metal film fusible, 1 watt.

I later learned that sometimes the following resistors should be changed out during a cap kit on the Sanyo 20EZV. The majority of cap kits out on the market do not include them. They are included in the Zanen kit and the Twisted Quarter kit. Failure of any one of these 3 resistors can cause vertical collapse after completing a cap kit on a Sanyo 20EZV.

R472 – 33 ohm 1/4w
R473 – 1 ohm 1/4w
R478 – 1 ohm 1/4w

Big thanks to Dave Okert and his Sanyo 20EZV Flow Chart, which is a great starting point for any Sanyo repairs!

Sanyo 20EZV Flow Chart
Sanyo 20EZ Troubleshooting Guide

Tempest monitor repair log – WG 6100 color vector monitor rebuild

Status: FIXED

Repair cost: About $50

KLOV Posthttp://forums.arcade-museum.com/showthread.php?t=98417

Symptom:  Monitor dead.  Original 6100, fireworks on deflection board, R100 burned through.

Diagnosis: Low voltage section of deflection board is toast.  Perform cap kit, install LV2000, concentrate on chassis transistors & power transistors on deflection board.


  • 08/02/2009 – Installed cap kit + extra parts, LV2000.  F100 & F101 blow immediately after powerup.
  • 08/18/2009 – Replace diodes, transistors on LV2000.  Replace blown (underrated) D100-103 with 6A2 diodes.  Replace Q603/Q703 on frame.
  • 08/24/2009 – Learn, inspect work, double-check, triple check…smoke test tonight.  Deflection board fixed – we have monitor chatter, but only half a picture.
  • 09/17/2009 – F600 now blowing on powerup.  Replaced blown Q606.  Powers up and runs for about 5-6 seconds with vertical line before F600 blows again.
  • 06/25/2010 – Replaced all frame mounted transistor sockets with new ones.  Monitor now powering up.  Issue with Tempest boardset (link), monitor verified working with another color vector game.


The frame-mounted transistor sockets were most likely causing intermittent/bad connections from the corroded and weakened leafs.  The intermittent connections were eventually leading to the transistors shorting out, causing a domino effect of other parts to fail, or a fuse to blow.  Every time a fuse would blow, the proper thing to do would have been to test all the transistors (on the frame and deflection board) for shorts before continuing.  Replacing all 6 sockets eliminated this issue.

Eventually, the culprit parts were the MPSU07/57 power transistors on the deflection board.  These parts are very expensive and/or hard to find, but I bit the bullet and replaced them all, which fixed the problem.

Pole Position 2 repair log – “hard right” steering issue

Status: FIXED

Repair cost: $0 (Used part from stock)

KLOV Posthttp://forums.arcade-museum.com/showthread.php?t=135387

Symptom:  Hard steering to the right sometimes registers as going in a straight line.

Diagnosis: Noticed encoder was smaller than encoder from a spare PP control panel I had.


  • 05/26/2010 – Current encoder being used seems to be from a spinner assembly.  Replace encoder with correct one, and steering is working fine now.