Too high voltage? (Solved)

[erwin_ve]

What did you measure: Ac, dc?

[norburybrook]

so from your transformer you've got 19v AC coming in and after the rectification 84mV? are your diodes knackered?


has your relay transformer got a center tap or are you using the wrong pair I wonder?




M

[erwin_ve]

I wonder if the wire from the top right positive side of the cap is going straight to the V reg pin 1? It seems like it's connected to the diodes, but is it?

Its connected to both.

[pompeiisneaks]

I'd also check what DC Voltage you're getting at the input of the voltage regulator (pin 1) then see if you get output at pin 3 that should be 12VDC regulated. If not either the voltage regulator is bad, or something is dumping the voltage down to earth somehow. You could temporarily desolder the wires from pin 3, if you're getting good input voltage, (make sure to wrap them up with electric tape or some such so they can't ground out etc while you're testing) and then measure pin 3. If, disconnected, you see 12VDC then the voltage regulator is working, but then something after it is drawing down the current. If no output you may have a bad regulator or something else there is off/wrong.

Then you should see 12VDC on the relays on one side but nothing on the other until the coil engages via either a switch or footswtich. (remeber to put your DMM ground connection on the ground of the voltage regulator to ensure you're in the right part of the circuit.

~Phil

[erwin_ve]

I'd also check what DC Voltage you're getting at the input of the voltage regulator (pin 1) then see if you get output at pin 3 that should be 12VDC regulated. If not either the voltage regulator is bad, or something is dumping the voltage down to earth somehow. You could temporarily desolder the wires from pin 3, if you're getting good input voltage, (make sure to wrap them up with electric tape or some such so they can't ground out etc while you're testing) and then measure pin 3. If, disconnected, you see 12VDC then the voltage regulator is working, but then something after it is drawing down the current. If no output you may have a bad regulator or something else there is off/wrong.

Then you should see 12VDC on the relays on one side but nothing on the other until the coil engages via either a switch or footswtich. (remeber to put your DMM ground connection on the ground of the voltage regulator to ensure you're in the right part of the circuit.

~Phil

Been there Phil, 1 or 2 pages back. A short somewhere for sure

[ericlc]

It is a matter a ruling out logical sections in the circuit. Since the output of the diode bridge is only a few mV's, I would test the diode bridge in isolation first. Unsolder components at the output of the diode bridge and measure the output with respect to ground. When that is the case, the next step is putting the first filter capacitor back in.

[Oddvar R]

so from your transformer you've got 19v AC coming in and after the rectification 84mV? are your diodes knackered?


has your relay transformer got a center tap or are you using the wrong pair I wonder?




M

This is the 12v transformer schematics. I am using red/yellow and black/orange.

[Oddvar R]

What did you measure: Ac, dc?

It is DC...

[Oddvar R]

I have now included a pic showing the voltage of about 20v, I have changed diodes to HER208, and when I measure from the same point with the black pin and the red pin to out V reg, I get the same reading. If i read V reg out to ground, close to no voltage? Any clues?

[pompeiisneaks]

The input voltage to the LM7812 isn't important so long as it doesn't exceed 35V which is the max voltage it can regulate.

Your voltages look fine coming out of the rectifier.

If you keep the ground connected where it is, then there should be 19.55VDC at the input of the LM7812. Then the output should have a nice 12VDC roughly coming out of it.

It seems like your input voltage is fine. Check continuity between the output of the diodes and the input pin of the regulator. Check the center pin to ground via connectivity too. (you should be good due to it being bolted to the chassis, and soldered to a pin that also has ground, etc. 3 separate ground points, but just double check continuity. If they all share the same ground, you should always see that 19VDC everywhere you ground anywhere on the chassis.)

~Phil

[Oddvar R]

One great step forward, but now I wonder how to measure or find the 12v? Seems like it's 19v everywhere, but only when I ground in the diode junction?

[erwin_ve]

One great step forward, but now I wonder how to measure or find the 12v? Seems like it's 19v everywhere, but only when I ground in the diode junction?

The wire that grounds the diode junction is broken?

[Oddvar R]

I am beginning to wonder if the V regulators are faulty somehow. I had two, and both of them shows the same value in and out? Is that even possible?

[erwin_ve]

Is the ground wire from the diode junction ok? Measure.
You do have the LM7812 voltage regulator?
Maybe You have a short in that area. It would check vreg out to ground in Ohm with amp off

[Oddvar R]

Happy message: The overdrive section works, I am a bit uncertain what happened, bu I resoldered all the parts in the chain, and suddenly the switch on the back indicated life. Both volume and overdrive works. Thank you guys, without you I don't think I would have made it this time.