Boss NS-2 -- polarity protection problem?

[1978]

Hello,

Problem the first,
I'm trying to fix a Boss NS-2 Noise Gate.  Here's the current problem:
The Threshold and Decay knobs don't affect the signal, and the effect sounds very weak, distorted, and "blatty".
On "mute" the signal is distorted whether effect is turned on or not.
On "reduction" the signal is distorted when the effect is on; when effect is off the normal guitar tone comes through.

I thought it was a wiring thing, but all connections seem intact.  Looking at the board, I noted right off that D1--a 1n4004--was literally blown apart, in two pieces.  I replaced that, but the same problem exists.  There is a 100uf cap next to it, which tests OK on my meter (that is, it says the value is 97-ish).  Could there be another part that is shorted?  Am I right in suspecting that someone used the wrong power supply and that that's blown something?  Or is the distorted/weak signal indicative of another problem not related to the power supply?

Problem the second,
I don't have a schematic of the pedal, so I don't know what to look for/where to look for it.  I've started by trying to check the other diodes.  My meter's instructions say to compare readings from anode->cathode and cathode->anode.  If one is overrange, the part is good.  However, when I put the new diode in, it's not giving one reading as an overrange.  Instead, with 
negative at cathode:  .521
positive at cathode:   .863

The meter's instructions say "if both values are very small or zero, the component is shorted."  Is  .863 very small?
Shouldn't one of the readings be overrange?  Could another part be affecting the reading (I'm testing from the component side, not from the pcb traces; also, all of this is without battery plugged in)
another diode - marked D6 - also has close readings; should I replace all those diodes too?

many thanks,
Kevin

[R.G.]

A good diode should show well over 1M on a resistance test the non-conducting way, and under 1K the conducting way. I don't say red lead and black lead because as I learned the hard way, some meters make the black lead positive on resistance tests. Not many, but some.

You generally can't test diodes in circuit, because there are alternate conduction paths in parallel with the diode so that one way you read the diode and the other way you read everything in parallel with the diode. You have to unsolder at least one lead to get a good test.

[1978]

R.G.-- thanks for helping; since I started experimenting five or so years ago, your pages have been invaluable to me.  It took me forever to respond because my multimeter crapped out; I think I blew a fuse that no one in New York has, so I got a new one as a stopgap. 

For the NS-2, I took the 1N4004 diode out and tested it; it's a good replacement. I also took the 100uf electro cap nearby out to test, because I think someone may have used an unregulated power supply and that that might be where the problem was.  It was OK.  So now I need to identify which other part is shorted (preferably without taking the whole board apart).   From looking at other posts, perhaps I've blown an IC or something--I was hoping it was just the first diode or maybe a cap.  I did get the schematic from someone, but it takes me forever to match it up with the PCB.

I think now I'll have to look back through the beginner posts to see if there's not some debugging for compressor/noise gates.  The Geofex debugging page has those as two "exceptions" for the "blatty" sound my pedal's making.  I"m going to check all the transistors, first, though and post the voltages to see if anyone can spot trouble.

best,
Kevin