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Williams Display Power Transistor Replacement

NOTICE: For some very important information, please read the Technical Article Notice and Disclaimer, found on our Technical Articles Index page before performing any of the work described below. The information given below assumes you have read the Notice and Disclaimer first.

Williams used two different types of transistors, and slightly different circuitry routing, for the display power supply circuitry on their games from 1977 through 1989. Here is a breakdown of the original part numbers, and their new replacement numbers:

Williams High Voltage Display Transistors- Cross Reference Part #'s:

Old Style (late 70's thru mid 80's):

Q1 SDS 201 = NTE 171

Q2 MPS D52 = NTE 288, 2N5400, 2N5401

Q3 SDS 202 = NTE 296

Q4 MPS D02 = NTE 287, MPSA06, MPSA42

New Style (mid/late 80's):

Q1 MJE15030 = NTE 54

Q2 MPS D52 = NTE 288, 2N5400, 2N5401

Q3 MJE15031 = NTE 55

Q4 MPS D02 = NTE 287, MPSA06, MPSA42

Looking for these parts? We have them in stock- see our Electronic Parts page for online ordering.

Note that the original early style Q1 and Q3 transistors are no longer available- in original or aftermarket parts (if you can find the NTE replacecments, consider yourself lucky). These parts must be replaced with the newer MJE15030 and MJE15031 parts. The MJE units are available as original parts, or NTE replacements. See our Electronic Parts page for online ordering on these parts. The MJE transistors had a different (standard) pinout than the original SDS type (non-standard), so they must be installed differently on the board.

Pinouts:

Old (SDS): E B C

New (MJE): B C E

Note that the new pinout is just shifted one place to the left. To install the new MJE type on a board that originally used SDS, do the following 4 steps:

Drill a new small hole to the right of the rightmost hole for the old transistor mounting- like this (the "x"):
```
o   o x
  o
E B C    (Pinout)
```
Insert the left two legs of the MJE transistor into the RIGHT two holes of the old mounting. The right leg of the MJE will go through the new hole you drilled. So the MJE transistor will basically be mounted one position to the right on the board. Like this:
```
  | | |
o   o x
  o
E B C E  (Pinout)
```
Solder the two left legs of the MJE transistor to the board.
On the back of the board, install a small jumper wire between the right leg of the MJE and the first hole of the old mounting. (ie: connect the leg that goes through the hole you drilled to the leftmost hole (empty hole) of the old mounting.)

Alternate Method:
Note that the MJE can also be installed without drilling a hole, but this can be a bit tricky (not advised). To do it this way, the left two legs must be installed in the 2nd and 3rd holes, respectively (as described above), and the rightmost leg will then criss-cross under the first two legs, and install in the 1st hole. (Click here for a picture) This is actually the way Williams recommended doing it in a service bulletin, but the above method with drilling a hole is much safer, cleaner, and you can still mount the transistor without any risky leg criss-crossing nonsense.

If you mount the transistor via the criss-crossing method, we strongly recommend installing some insulation on the rightmost leg (such as heat-shrink tubing, etc) to prevent any arcing or shorts to the other legs. And as always, these modifications are done at your own risk- we are not responsible for any damage to you or your game. Use caution, and good luck!

Optional:
Williams recommend upgrading resistors R2 and R5 to 1/2 watt 1.2K ohm resistors for better reliability.

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