Noob opens first pedal: Malfunctioning Boss HM-2

[FiveThumbs]

Hi. First post.

I was given a broken HM-2 years ago by a friend. I just saw the resale value on eBay today and I thought I would see whether it was fixable.

The sound is thin and fizzy and quiet. It gets more distorted when I hit more than one guitar string (which I expected) and also gets quieter (which I didn't expect.) The LED indicator looks dim when the pedal is active but I don't know how bright it is supposed to be. The behaviour is the same whether using a battery or an AC adaptor.

I just took the back off the pedal and pulled the free end of the circuit board up, bending the stiff ribbon cable in the process.

At first, I thought the output jack could not be correctly connected. Two of it's three tabs have never seen solder. But I guess the metal case is connecting it to ground.

Some of the components have a brown gunk on them. It looks like toffee and feels firm to the touch. On the solder side of the board there seems to be a clear glue in a couple of places.

I assume this is too little information for anyone to make specific recommendations. I'm willing to invest money in acquiring equipment and skills. I don't have any income at the moment but I assume that selling the pedal (even as not working) could cover the outlay, and I assume that would be fun. Any pointers on what I should read or watch or acquire to make a start on this?

[The Dude]

Schematic link attached. The first thing I'd do is check that the 9V supply is up to snuff when the pedal is connected and on to verify that there isn't something shorted or leaky loading down the supply. Also check the 4.5V supply.

https://www.hobby-hour.com/electroni...-schematic.png

[loudthud]

Boss pedals of a certain vintage require a Boss 14V unregulated adapter which can only power one pedal. These pedals require modification to run on the common 9V adapter used on most pedal boards. Someone may have improperly attempted to modify your pedal. The pedal first needs to be returned to stock form so that it operates properly on a 9V battery.

What needs to be done is that R2 and D1 (see schematic linked in The Dude's post above) need to be removed from the circuit board and each replaced by a short wire. Look around on the Net to find the layout for the PCB in your pedal. This should allow the pedal to function with a 9V adapter.

[J M Fahey]

Interesting dirty trick, it FORCES user to buy the original adapter or else.

And D1 "floats" it so it can not feed anything else, I bdt it costs, sy, 60% or more what raw pedal does.

Oh well.

[g1]

This article says basically the same as what loudthud mentioned above, and lists the component designations involved for other Boss pedals: https://stinkfoot.se/archives/1019

[FiveThumbs]

Thank you so much!!

I plugged a 12V centre-negative adaptor into it and it sounded like a regular distortion pedal.

I guess the battery I tried must have been too low on charge.

It looks like I have a working HM-2 ))