Category: General

Atari rheostat volume knobs!

Once in a while, something so simple comes along that it just deserves to be discussed and shared. Then you start to wonder, “how did I get along without that for so long?”

During my last Bob Roberts order, I was perusing the website to make sure I had everything I needed. I knew that Bob sold volume/pot knobs — and quite a variety at that — but this time I noticed that a few were specifically aimed at the infamous finger-crushing Atari rheostat.

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Let’s back up for a second…what the heck is a rheostat??

Many typical potentiometers are designed for 250 or maybe 500mW. A rheostat, on the other hand, is engineered to dissipate much more power, and are therefore typically rated for several Watts.

In games where the volume adjust is working on a low-level audio signal, a regular potentiometer will suffice just fine. However, on some games, because Atari wired their volume adjusts after the amplifier, something that can handle more power needed to be used. Some of the games that used them are Lunar Lander, Asteroids Deluxe, Battlezone, Firefox, Major Havoc, Missile Command, Pole Position, Red Baron, Space Duel, Tempest & Warlords.

Ok…so, why did Atari use them? Well, in simple terms, it was most likely just an engineering decision. Atari’s gameboards of the time output the volume at full blast. The rheostat was connected directly to the speaker lines. Thus, a wirewound rheostat had to be used because of it’s wattage handling capabilities.

In this case, an Ohmite 50 Ohm, 12.5 Watt rheostat was used, Atari part #RES50R.

So, anyone with one of these older games knows that these old Ohmite rheostats are painfully difficult to turn, mostly because of their mechanical structure – a thick wiper element that runs along a large, heavy wirewound base. I’ve heard it described before as “trying to turn a slippery toothpick.”

So…back to the knobs on Bob Roberts’ website. I got the $2 version, and let me tell you…this is the best $2 I’ve spent in a long while. My Pole Position II, Tempest and Missile Command all got one, and my fingers have never been happier…

Sanyo EZV-20 monitor repair log – HV shutdown

Status: FIXED

Repair cost: About $18

KLOV Post:

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


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.

Frenzy repair log – RAM pattern on start


Repair cost:  $20

Symptom: 3 beeps, colored RAM pattern on startup

Diagnosis: Interconnect cables bad (were previously removed & reseated to test another board)


  • 9/23/09 – Replaced 3 connectors with SCSI cables.  No change.  Found DIP switch thrown which was causing it to stay in test mode.  Flipped SW1 open and game booted.


Self-test beep pattern on start
A series of 8 self-tests occurs each time the game is powered on, or reset.  The LED is on the ZPU-1001 board and each flash is accompanied by a tone.  The test will stop at the malfunctioning circuit, provided all the boards are connected properly.

1st beep – ROM circuits on the ZPU board
2nd beep – “scratch pad” are of the RAM on the ZPU-1001 board
3rd beep – Screen RAM on the VFB-1000 board
4th beep – RAM circuits on the BSC-1000 color board
5th beep – Shifter/flopper circuits on the VFB-1000 board
6th beep – Arithmetic and Logic Unit (ALU) on the VFB-1000 board
7th beep – Interrupt and Non-maskable Interrup (NMI) circuit portions which are on both the ZPU-1001 and VFB-1000 boards
8th beep – If the game still does not work, malfunction is in a circuit outside of the self-test program