Sequencer LED Replacement and Stage Jump Elimination
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Author:  ModularMe [ Thu Mar 07, 2013 11:58 am ]
Post subject:  Sequencer LED Replacement and Stage Jump Elimination

Scott had some helpful troubleshooting advice on the 12 stage PAIA 4780 sequencer:

Hi Scott,

Do you have information on the red LEDs used in the PAIA 4780 sequencer and also 4700 modules like the ADSR? I’m looking to replace a few LEDs. In the manuals they are listed as “MLS-750” but no other specs are provided.

- Ralph.

Hello Ralph.

Here is a link to what looks like a functional equivalent on the Mouser website:

At least it looks to be the same size, and red. Red LEDs generally have a 2v Vf and require a few to about 10 mA of current to light (generally, interchangeable).

- Scott


Thanks, I replaced the sequencer LEDs with the part from Mouser that you recommended, and success, it works nicely. Slightly brighter than the original (which looks even better.) so I replaced all at once. It takes a bit of disassembly to get to the LED PCB sub-board (particularly the second lower one).

I have a suggestion that may eliminate the problem mentioned by others on PAIA talk that causes the sequencer to jump ahead one or more stages. It’s a substitution of a RadioShack switch for the original red pushbutton to eliminate the switch bounce. The RS switch fits nicely in the LOAD and STEP mounting holes with no panel modifications needed.

Part number 275-1549, mini SPDT 3-Amp Momentary Pushbutton Switch, $3.99, available in-store.

Be sure to get the switch with the black button. The identical looking switch with the red button is a toggle on/off and not momentary.

Other brand switches will probably work, this just happens to be the one I tried.

The switch substitution has eliminated stage jumping, with one exception, and this only occurs on one of my two sequencers: Pressing LOAD causes a load of stage one and an immediate jump to stage two. If I press and hold LOAD, stage one lights as it should, but releasing the button causes a jump to stage two. If I use bare wire instead off the pushbutton switch, I can make it behave. For some reason, LOADing the first stage is very sensitive on one of my two sequencers. Still, much better than before.

- Ralph

Hello Ralph.

Thanks for letting me know. The pushbutton switches we stocked back then were susceptible to getting resin from soldering or tarnish since they weren't tightly sealed and this contributes to unreliable contact.

Sometimes the Load-going-to Stage-Two situation can be corrected by substituting a 220k for the 270k at R75, and/or, adding a 0.001uF capacitor with one leg on one terminal of the switch and the other leg on the other terminal of the Load Switch.

- Scott


Replacing R75 (270k) with your suggested value of 220k has corrected the Load-going-to Stage-Two situation. Since the resistor substitution corrected the problem, I didn’t have to add the .001 capacitor. Now everything is working properly.

Thanks for all your help,


Author:  Kyhotay [ Mon Mar 11, 2013 6:45 pm ]
Post subject:  Re: Sequencer LED Replacement and Stage Jump Elimination

Scott, is there an easy way to construct A LED PCB for the sequencer? I see blue LEDs in my future.


Author:  ModularMe [ Mon Mar 11, 2013 11:13 pm ]
Post subject:  Re: Sequencer LED Replacement and Stage Jump Elimination

Prior to using the LEDs recommended by Scott, I experimented with other LEDs. I used a popsicle stick to temporarily mount the LEDs and place them in the sequencer. When you trim the length the popsicle stick is just about the same width as the LED PCB board. Use the front panel as a guide to mark the LED locations. The only wiring is the connection of the common leads, so an etched PCB is not completely necessary, as it's just a mounting device. Other pieces of stiff flat material should work as well. The LEDS stayed in place with pressure but I would add a dab of epoxy for a more permanent mounting. Not elegant, but it works, so you could remove your working red LED strip and try a different LED color without the risk of damage from unsoldering all those LEDs.

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