Why extenders?

When repairing computer circuit boards, you must measure their signals.
To measure their signals, you must add some signal clips.
To add signal clips, the boards must be operated outside the card cages.

dec quad extender original

That's why you can not repair DEC PDPs without so called "Extenders".

These come in several widths, identified by the number of 2*18 pin flip chip sockets they provide: "single-slot", "dual-width", "quad-width" and "hex-width". They have regulary DEC module numbers, for example: the quad-width is W987A, the dual-width is W984A. For dimensions see attached PDF.

pdp1134 extended boards

Extenders even can be cascaded ... usually not a good idea!

Where to get them?

Extenders are rare, as nobody gives them away.

But there is at least one company which is still selling them: douglas.com


Here is a project to build extenders on yourself. Extenders consist of the circuit board and Flip-Chip sockets soldered to them.

dec quad extender diy


Attached below are Gerber files for single, dual, quad and hex-width circuit boards, each in standard DEC form factor, and in a "+5" variant, elongated by 5 cm.

extender pcbs 1246

You can view Gerber files with https://www.gerber-viewer.com/

These chinese board makers can produce at reasonable prices. For example, for a batch from jlcpcb.com we had in january 2020 (including shipment to Germany and taxes): Single = 8€, dual = 8.50€, quad = 15€, hex = 24€.

OK, we had quite a volume:

extender pcbs many

The "+5" variants let the sockets look above neighbor cards. This allows to attach clips to the socket wires.
Or you solder on rotated sockets, like in this strange PDP-10? extender:

pdp10 extender rotated sockets - pdp10 extender rotated sockets back


Flip-Chip connector sockets

These black DEC connector blocks are also rare. Note "rare" like in eBay advertisements, but really really rare.

dec flipchip socket

Some of us guys harvested them from dead backplanes. Steps are

  1. unwind all the wire-wrap from their pins (very boring)
  2. cut the PCB with sockets into handy pieces
  3. unsolder socket pins and remove sockets from PCB.

The latter may be easy or impossible, depending on the backplane maker style.

Some 3rd party backplane consist of separate sockets.

backplane dataram

DEC backplanes use sockets in quad or niner-packs.

backplane dec quadblocks

These can only be separated by sawing through the blocks. I successfully used a tile-cutter with diamond blade, as the socket bodies seem to consist of Bakelite, which behaves quite mineralic.

Unsoldering from DEC backplanes once was not too difficult, as PCB holes have some air around.
On some other DATARAM backplane we found the pins to be pressed into the PCB ... no chance here!


There's also a company named "ECS" which sells single-width connectors, see attached datasheet.

We got an offer of about $9 / piece in a quantity of 300.
So you have $56 for a hex extender, and have to find lot of other interested people, not to mention the effort to manage distribution ... lets see if this ever happens!

2418-13-30.pdf -- ECS flip chip socket dimensions

gerber-single.zip --

gerber-dual.zip --

gerber-quad.zip --

gerber-hex.zip --

gerber-dual-5.zip --

gerber-single-5.zip --

gerber-quad-5.zip --

gerber-hex-5.zip --

flipchip-dimensions.pdf -- DEC board dimensions

2400-Series125-X-150-Contact-Spacing.pdf -- ECS flip chip socket datasheet