DOD American Metal

Another quick one. This American Metal would power up, pass a clean signal but wouldn't pass an effected signal.

Schematics are older DOD pedals aren't too hard to come by (I believe some of them were supplied in the original boxes). I suspected a bad switching JFET was blocking signal, but they all measured fine on the oscilloscope.

I found that two of the transistors near the distortion control had very little voltage on the collectors. The schematic shows a series 1k resistor and a 47uF capacitor from the 9V supply, so there's a good chance that capacitor is shorted.

The 47uF is right in the middle of the PCB. Pulling out brought back the effected signal, so I replaced it and put things back together.

This is a very cool pedal, definitely in the HM-2 family. Maybe not as much gain and not as much EQ control, but it certainly does the buzzsaw sound when turned up.

Digitech PDS 8000

I got this one for completeness sake after looking at the other PDS series.

The insides are very similar to the PDS 2000, with 4 times the memory. The PDS 8000 schematic is online, but the quality of the scan is so poor that the 2000 schematic is probably more useful.

As arrived, no activity. The reverse polarity diode was shorted, after clipping it out I had 5V at the digital chips but no 9V at any of the analog stuff.

I knew that the 9V supply has a soft-start circuit (as in the 2000) - the JFET was also dead. With a repaired soft-start, the 9V rail was shorted to ground. There is only one 470 uF electrolytic capacitor from 9V to ground, replacing this fixed the pedal. It also got new footswitches as the old ones were prettyy unreliable.