Memory faded and trying to remember...
Original Stern MPU to sound board ribbon cables -- single row and I believe they used two 17-pin ribbon cables that were 1x17 with 0.1" centers? Is this correct?

Found this on Pinwiki (I should have looked there first!):

"The Stern SB-300 sound board was used in all games which used the M-200 MPU board. The SB-300 is interfaced to the MPU board via the 34 pin J5 connector located at the top of the board. Note that the sound board only uses pins 1-32 on its J1 connection. Some ribbon cables used were 2 - 16 pin connections, while others were 2 - 17 pin connections, or a combination of the two. Make certain that pin 34 of the sound board is not connected to the MPU. Pin 34 on J1 of the sound board and pin 34 on J5 of the MPU board is the /IRQ signal. This signal is never used by the sound board. However, if it is connected to the MPU board from the sound board, it can sometimes cause the MPU to lock up or hang. Either bend pin 34 of J1 on the sound board away from the connector (if it is even connected), or snip the pin off completely."

A14 is not used on the sound board BUT the IRQ signal is connected to the IRQ on the sound board... AND you don't want the sound board IRQ to be hooked up. This would explain the 2x 16 pin plugs. Or the 2nd using an 18 pin plug with two last pins not used.

I have a source for the 0.1" ribbon cable (very tough to find!) as well as crimp on 0.1" single row plugs (also very tough to find). I'm going to try for 16 conductor cable and 16 pin plugs and see if I can get them.

Next question -- what was the typical length for these?

Thanks guys,
Ed

Thx.
I'm thinking two identical cables, with 17's at 12" long is the way to go. For those that don't want the IRQ connected, notch that connection on the ribbon cable.

Ed

OK -- I finally received a bunch of Stern sound cables. Sell them in pairs. Either 2x 16 conductor or as 2x 17 conductor. This covers those that use 32 pin interconnect and 34 pin interconnect.
No photo's yet, though. Gray cables, black plugs, black stripe for pin 1 indicator.

They can be found here:
https://www.greatplainselectronics.com/products.asp?cat=57

Resurrecting zombie posts before restocking ribbon cables.

Does anybody know of an old Stern with an SB-300 that MUST have the 34th pin (IRQ) hooked up between the sound board and CPU board?

For MPU-200/SB-300 connections:
I have read posts that said if a 34-pin connection is used then some boards didn't function properly. Probably due to software mishanding of the IRQ.
And some posts that have 34-pin connection installed, have IRQ disconnected and it works fine -- which says these CPUs do not use this IRQ.
And some posts that have 34-pin connection installed, have IRQ connected and it works fine - which says CPU properly handles IRQ (don't know if it uses it, though).

So what I need to know - do any boards *need* the IRQ signal on pin 34 to be passed from the SB-300 to the MPU-200? Can all these machines get by with just a pair of 16 pin connections? I know the following had 34 pin cables originally used (e.g. 2x17 or 1x18 cables) BUT can all the MPU-200/SB-300 machines use the same MPU-100 cables with a 32 pin count?

The games affected:
Meteor
Galaxy
Ali
Big Game
Seabitch
Cheetah
Quicksilver
Stargazer
Nine Ball
Iron Maiden
Viper
Dragonfist
Cue
Flight 2000
Freefall
Lightning
Split Second
Catacomb
Orbitor 1

Wow, now there's an answer!

OK -- so apparently in the machines that do work properly with 34 pin plugs, they make sure that the 6840 timer doesn't generate an IRQ. This can done by making sure that the composite interrupt flag within the PTM is never set.

Pin 33 carries A14 which is not used at all by the SB-300
Pin 34 which carries the IRQ from the timer back to the CPU but if the IRQ occurs then the CPU doesn't know what to do and reboots.
So this confirms that posts above and others in pinside and rec.games.pinball - these machines don't really need 34 pins connected, only 32. So it makes most sense to only stock cables for 32 pin connections.

Thanks much, Ed