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4780 Issues

Posted: Tue May 22, 2012 8:06 pm
by Kyhotay
Hey Scott,

Pretty quiet on the board this month, eh? Let's make some noise, shall we?

I picked up a 4780 Sequencer on eBay last week. I temporarily connected the Watt Blocks to the 4780, turned it on, and everything functioned fine. I didn't hook it up to a VCO but confirmed that the voltage swings were from near zero to about 5V (although step 9 is a tad over 6V). I checked all the pin outputs as well as the gate & trigger outs. Again. all worked as expected. However, when I soldered the power connections step 12 is not outputting a CV. The gate, trigger and pin outputs are fine but no CV, nor is the LED working.

Any thoughts on what I should look for?

Two other minor points: When the tempo knob is rotated past a certain point (about 3/4?) the sequence stops dead in its tracks. Back off the pot and it starts where it left off. Not sure this is a concern or not, especially in light that I want to run the sequencer off the Master Synchronizer one of these days...

The other question is if you have a recommendation for better push switches than the ones originally provided. Even back in the day the 4780 would skip way ahead if you even looked at the push button wrong. Maybe switch technology has advanced? I have the same issue with the program push button on the Proteus.

Thanks for any help or sage advice!

Brian Folkes

Re: 4780 Issues

Posted: Wed May 30, 2012 2:14 am
by PAiA-Scott
Check the resistance of the pot vs the schematic. It might be marked on back. Maybe the builder got one in place of another. Maybe some flux or other gunk is coating part of the resistive element and the wiper is loosing contact.

The LED is a part of the CV output circuit so if it looses a connection it would stop the output. They're tiny and delicate in the sequencer, so be careful when looking for trouble in this area. A joint might be borderline and movement or stress might have opened the circuit in the connections to the this part of the LED board.

The p.b. switches can get stuff inside them that some alcohol and repeated operation might clear. Sometimes just a quick tap is better than a push in terms of preventing multiple actions due to make/break contact with the button pushed down. I've seen some toggle switches that are momentary contact and these might be an improvement if the seal is good and air and contaminants can't get at the contacts.

Re: 4780 Issues

Posted: Wed May 30, 2012 12:54 pm
by Kyhotay
Thanks, Scott. I'll give it a try this afternoon.

Are you back in town already? I thought you were on vacation!


Re: 4780 Issues

Posted: Sun Jul 15, 2012 6:36 pm
by Kyhotay
F/U: Finally got around to looking deeper into the LED issue. After I pulled it from an old style wing cabinet it worked fine. Put it back in and step 12 was out again (message?). I tweaked the board some and remounted it and all is well.