Skip Navigation Links
 Home 
 WANTED! 
 Library 
 Testimonials 
 Press 
Parastream Technologies Logo Search | Cart


Sign In
Skip Navigation Links
 Software Expand Software
 Hardware Expand Hardware
 Consulting Expand Consulting
 Support Expand Support
 Free Stuff 

IMSAI CP-A

IMSAI CP-A Rev 4The CP-A board is the operator's panel for the IMSAI 8080 System. It includes operator switches, indicator lights and all logic necessary to operate the IMSAI 8080 System.

Contents

Visit our Facebook group for announcements, discussions, and more information about supporting the IMSAI CP-A.

We put a lot of time into creating, gathering, and organizing the information in this page. If you found any of this to be useful to you, especially if it helped you to make or save money, please  to help us continue making content like this available.


Sourcing Switches

Over the past 20 or more years, much effort has been made by numerous individuals to source the iconic paddle switches which went out of production in the late 1990s. This guide is helpful to find new old stock switches, but it is also helpful if you are mixing and matching switch frames and actuators. If you are adventuresome enough to print your own actuators, you still need to know what switch and frame to start with. We’ll even help you source new alternative switches.

Let’s start at the beginning with the original IMSAI CP-A switches. The following table shows the original IMSAI CP-A switch cross-reference and BOM.

Qty IMSAI P/N C&K P/N Description
8 26-1500001 7101J47 Blue Paddle Switch, on/none/on
8 26-1500002 7101J43 Red Paddle Switch, on/none/on
2 26-1500003 7105J47 Red Paddle Switch, momentary
3 26-1500004 7105J43 Blue Paddle Switch, momentary
1 26-1600001 7101J33 Red Rocker Switch, on/none/on

The C&K part numbers in the table are most likely the ones as ordered by IMSAI purchasing. They are very simple part numbers that specify the switch configuration, the actuator type, and the color. Everything else is default. This is based on forensic analysis of original IMSAI switches and examining C&K catalogs from 1986, 1987, and 1993. The 1986 catalog was most helpful as it best explained what the default options were closest to the time IMSAI was producing the CP-A. If you are searching for old stock of these switches, try adding Z, ZQ, or ZQI before the last digit to find the exact switches IMSAI used. For example, 7101J4ZQI7.

Seeing how unlikely it is that you will find these exact switches these days, let’s discuss options. While the 7101 and 7105 model numbers cannot be changed, the rest of the options are somewhat negotiable.

Actuator

The actuator is a major part of the iconic look of the IMSAI 8080 system. The IMSAI CP-A used a J3 rocker and J4 paddles. The J3 is the only actuator currently in production. The following table shows the actuator options that are all interchangeable with each other. If you are willing to make a statement, some of the alternative paddles might be an option for you.

Option Description Comments
J3 Rocker Used in the CP-A power switch.
J4 Paddle Used in the CP-A for all except the power switch.
J5 Tapered paddle Might make an interesting alternative look.
J10 Large rocker Unsuitable for use in the CP-A, but the switch and bracket are compatible with J4 or J5 actuators in momentary-only applications.
J47 Paddle Identical to the J4, but the switch bracket is incompatible with the CP-A. You might be able to harvest the actuators from a switch to use on an existing switch, or a switch with the wrong color actuator.
J57 Paddle Identical to the J5, but the switch bracket is incompatible with the CP-A. You might be able to harvest the actuators from a switch to use on an existing switch, or a switch with the wrong color actuator.

The following table shows the actuator colors. Black is the default if not specified in the part number. Some of the colors are somewhat unique to C&K and other manufacturers such as NKK’s “equivalent” colors will be off.

Option Color
1 White
2 Black
3 Red
4 Orange
5 Yellow
6 Green
7 Blue
8 Brown
9 Gray

While the IMSAI colors are red/blue, there are other contemporary color combinations that might be cool if you can find them: white/black, white/gray, black/gray. All one color is another option. Just about any combination of red, orange, yellow, and brown would give it a definite ’70s feel.

Termination

The termination option is somewhat flexible if you bear in mind that the CP-A switch mounting holes are drilled for the larger Z terminals. The following options should work but would require assembly precision to align the switches: Z3, C, W, W1, W2, W3, W4, W5. Be advised that all except the C option will include epoxy sealing by default; read the paragraph on terminal sealing for cautions. Most of these options will also require the terminal leads to be trimmed after soldering.

Contact Material

The 40+ year old switches we have as reference show the telltale black tarnishing on the terminal silver plating. After the IMSAI CP-A production runs were over, C&K added contact material options that continue to the present. The following table shows the available contact material options and how they apply to the CP-A.

Option Description Comments
B or K¹ Contacts & Terminals: Brass, with gold plate over nickel plate. Rating: ≤ 0.4VA @ ≤ 20VAC/DC. (Std. with all termination options except Z, C, Z3) Best for all except the power switch.
Q or M¹ End Contacts: Coin silver, silver plated. Center Contact & All Terminals: Brass, silver plated. Rating: 5A @ 120VAC or 28VDC; 2A @ 250VAC. (Std. with termination options Z, C, Z3) All CP-A switches use this option. A good choice for the power switch, a poor choice for all others.
G or L¹ End Contacts: Coin silver, with gold plate over nickel plate. Center Contact & All Terminals: Brass, with gold plate over nickel plate. Rating: ≤ 0.4VA @ ≤ 20VAC/DC or 5A @ 120VAC or 28VDC; 2A @ 250VAC. Best of both worlds. When used as a power switch, the gold flashing burns off and it functions as a silver contact switch.

¹ These options have the same contact material. The terminals are copper alloy, with tin-lead alloy over nickel plate.

Terminal Sealing

The IMSAI switches were unsealed. While this might not seem to be the best choice at first glance, it is what the CP-A was designed for.

Option Description Comments
(None) No seal. Std. with Z, C terminations, not avail. with all other terminations. Original IMSAI specification.
E Epoxy seal. Std. with Z3, W-W5, A, AV2, V3-V9 terminations. Might interfere with proper mounting of the switch onto the circuit board.
I No seal for 71xx switches. Available only with Z, C, Z3 or W-W5 terminations. Used to override the default epoxy seal with Z, C, Z3 or W-W5 terminations.

Here is an excerpt from the IMSAI CP-A manual regarding the soldering of switches:

When the entire row has been spaced accurately, the board should be turned over and a center switch should be soldered in place taking care that the board is not bowed towards or away from the switches. When the board is positioned correctly, there will be a small space approximately ³⁄₆₄ inch or slightly under ⅟₁₆ inch between the bottom of the switch and the front of the front panel board. The two end switches should be similarly checked to make sure that the spacing to the board is correct and soldered in place, and then one switch each at the ¼ positions checked as to spacing from the board and soldered into place. Then the remainder of the switches can be soldered. Examine visually for solder splash or bent/unsoldered pins.

It’s probably fair to say that the expected gap between the circuit board and the bottom of the switch is about 0.05 inch. This is less than the 0.075 inch max depth of the epoxy seal. This means that if you choose switches with the E option, you may have to remove some of the epoxy sealant to get the switches to seat properly on the circuit board.

As it turns out, C&K is currently producing (as of 2022) the 7101 and 7105 switches with the black J3 rocker actuator. Unfortunately the J4 paddle actuator has been discontinued. If you can find other switches with the J4 paddle (or print some), you can swap out the J4 for the J3.

NKK Switches

NKK currently manufactures compatible switches to the old C&K line that appear to be better switches. The switches are the M series.

M2012TY replaces the 7101. M2018TY replaces the 7105. The next letter of the part number is the contact material.

Option Description Comments
G Gold; Rated 0.4VA max @ 28V AC/DC max Similar to C&K B. Best for all except the power switch.
W Silver; Rated 6A @ 125VAC and 3A @ 250VAC. Similar to C&K Q (default). A good choice for the power switch.
A Gold over Silver; Rated 6A @ 125VAC & 0.4VA max @ 28V AC/DC max Best of both worlds. When used as a power switch, the gold flashing burns off and it functions as a silver contact switch.

The next two digits are the terminal code. The solder lug (01) is identical to the C&K Z terminal used in the CP-A, but the Straight PC (03) should also work with some additional assembly care.

If you order a switch with just the above information, it will come without a rocker or paddle. You can order them separately (see below). If you want the rocker, add a -J and a color code. To order a paddle, add a -H and a color code.

The following table shows the actuator colors. Note that we have only compared the black, gray, red, and blue colors with the C&K. C&K orange and brown are not available in the NKK line.

Option Color Comments
A Black A tiny bit darker than the C&K. Nearly identical.
B White We have not compared to C&K white.
C Red A little darker than the C&K.
E Yellow We have not compared to C&K yellow.
F Green We have not compared to C&K green.
G Blue Much lighter than the C&K.
H Gray Much lighter than the C&K. Almost a yellow-green hue.

If you want just the paddles, Mouser has a few as of May, 2022. The part number is AT4156 for the rocker and AT4157 for the paddle, and uses the same color chart as the switches. They fit either the NKK or the C&K switch base. Our advice is that, aside from the black, the colors are too far apart between the NKK and C&K to mix in close proximity.


DYI Resources

We put a lot of time into creating, gathering, and organizing the information in this page. If you found any of this to be useful to you, especially if it helped you to make or save money, please  to help us continue making content like this available.

Manuals

Datasheets

 


Contact Us  |  Feedback  |  Ordering  |  Privacy  |  Legal  |  Partners  |  About

© 2022 Parastream Technologies, Inc. All Rights Reserved.