Nomad Schematic Question

[frets70]

Just picked up a Nomad 100 head in a trade--it's in very good shape, sounds great--I did discover that it had been modified.

It's looks like some sloppy mods, but as I said the head and footswitch function fine except for 2 small things.

1. The Power Jewel light does not come on
2. The EQ indicator LED does not come on

All amp functions are perfect, have played about 10 hours on it with no problems.

My question is this--

without taking it to an amp tech and having it restored to factory spec, are there ways around pulling power from the circuit board to make these indicator lights function correctly?

I am including a pic of some of the schematic with the Jewel light power--it seems kinda confusing due to the fact that it shows 3VAC coming into both conductors but no grounding point ( I must admit that I am a schematic noob--but understand electricity very well)

I did get the jewel light to come on correctly by grounding one of the legs, but this may not be correct and also puts the light operating at about half power (3.1 VAC)

I also have figured out how to make the EQ indicator function correctly (seems to me it burned out the original LED due to the fact that the modder slammed it with 3.6 VDC--ouch) I have a new LED that functions at 2.1 volts and just need to pick up a resistor to make it work (as long as my hot connection does not affect the rest of the amp.

Any help would be appreciated, I am not an amp builder, BUT I do know how to discharge caps and do basic component level testing.

Pic below

 

[Koreth]

Can't speak as to why the Pilot light doesn't light up when connected across the 3VAC lines, unless both legs were connected to the same line when you found the amp.

I'd just put the new LED in the circuit as it appears in the schematic. It really shouldn't matter who much voltage is applied to the LED, so long as current can be kept in check. Once enough voltage is applied to the semiconductor junction in the LED to forward-bias it (turn it on) it should light up and be just fine. Just make sure that you aren't going to get too much current with that 560? resistor (check the spec sheet of the LED you intend to replace the dead one with). Also make sure you don't put it in backwards, as only zener diodes are designed to handle the current to be had when reverse-biased past their breakdown voltage.

 

[frets70]

The Graphic LED can't be installed according to the schematic due to the fact that a resistor has been put in the spot where the LED connects on the PCB (the resistor is installed in a "on end" through the hole contacts) so the voltage has to come from another location.

My DMM reading show way different voltages on those contacts now.

I did find -1.8v on the channel selector switch could I reverse anode and cathode on the LED and use that for power?

Also the 2 green lines coming out of the trasformer are carrying the 6Vac needed for the Pilot Lamp--They go to the Power Tube circuit board--could I pull parallel lines from there to power the lamp. I do have the lamp working at half power--played 2 gigs this weekend and no problems.

thanks

 

[Koreth]

I'm confused by this. Can you take some pictures and post them? I'm having some trouble visualizing what you describe.

If it helps, I can try to take some pictures of the guts of my Nomad. Mine is bone stock, so comparing pictures of your modded nomad and my stock Nomad might be useful in attempting restore yours to stock spec.

 

[frets70]

I will take some pics tomorrow and post them, it is strange.

If you have any pics I would love to see a stock Nomad 100

 

[frets70]

Finally got to the pics, I have circled the areas in question with yellow.

Here is the resistor in place of the Graphic EQ LED

The long oval in the middle left of the photo is where the mini toggle switch for the Graphic EQ is connected in stead of the two contacts directly above the filter caps. The small oval in dead center is where the de-mud caps have been removed from the PI circuit

bottom circle shows where I grounded one of the Pilot light contacts to complete the circuit to light up the power light--although it only supplies 3.1VAC. Top left circle shows the pilot light contacts--Each one is supposed to be 3.1 VAC (for a total os 6.3