How to use Extron sync hardware with the X68000

[TD-Linux]

The X68000 sync lines are a bit strange - they are open collector, with a 1k pull up resistor. This is too weak for some hardware, including Extron sync combiners like the 192. These use a 510K pull down resistor. Luckily, this can be easily fixed. Remove the 5 body screws, plus BNC and VGA nuts, and pull out the PCB. Look for two resistors labeled 511 - R84 and R85 in this case - and remove them. This won't affect using the Extron with other sources.

When shopping for Extron boxes, make sure to find ones that go down to 15Khz. The 192/198/etc are fine, avoid the SS 200 and similar.

[hyrulebr]

Hi, I use now a Extron 580xi to joint sync to a bvm (15khz) but in the past used a couple of others extron models with sucess. Do you think that only model 192 requires this mod?

What happens when you use the 192 without modification? No signal at all?

[TD-Linux]

It's possible that later Extron models improved the sync sensitivity, or changed their internal termination.

An unmodified 192 will fail to see the sync signals (orange LED). A SS 200 doesn't have an indicator but will likewise not output any sync signals.

[Jehuty]

Could this be used on an Extron VSC500 ? The VSC500 doesn´t sync with the X68000 while it does with an FM TOwns.

[hiker]

VSC500 spec sheet mentions sync input impedance of 600 Ohm, so might work.
I recently replaced 510 Ohm resistors of a 203 Rxi with 10k Ohm because it didn't sync with X68k and I saw in the manual of other Extron devices that some have a switch to toggle between 510 Ohm and 10 kOhm.

[incrediblehark]

Interesting if it does work with the VSC500... I  have a VSC700 that I may need to try this with

[Jehuty]

Yesterday i opened my VSC500 and searched for the Pulldown resistor. I found R9 and R25, both 600 Ohms which go from H/V Sync to GND. Removed them and on the first test the Extron says "Out of Range". But after some seconds it sync the X68000 and it works. Several tests later, also tested with my XVI the message out of range doesn´t come again.
So it seems that removing R9 and R25 did the job.