Dead Metal Zone MT-2

[Chrisq206]

What are some good places to look for problems? I've looked over the connections many times and can't find any loose or disconnected wires. The light comes on and bypass mode works, but no sound when effeect is on. When I got it the diode near the AC adaptor (D6) was broken.

Any one w/ experience trouble shooting this one? Let me know.

[edvard]

I assume you fixed the diode and it's facing the right way (else the bypass and light wouldn't work).
Check that your soldering didn't overlap something else.
Do you know how the diode broke?
Was it broken as if someone pulled or smashed it, or could it have burnt and cracked?
If it has evidence of burning, then it may have been hit with a powersurge and you may have downstream parts burnt out.
Since the bypass works I'd suspect the op-amps next.

[Paul Marossy]

If it has evidence of burning, then it may have been hit with a powersurge and you may have downstream parts burnt out.
Since the bypass works I'd suspect the op-amps next.

+1. Most likely many of the active components got fried if it was exposed to an overvoltage condition.

[Chrisq206]

I'll have to check that out when I figure out how to spot dead chips. Can you tell me how to check for dead componets? I have a multimeter.

[Paul Marossy]

I'll have to check that out when I figure out how to spot dead chips. Can you tell me how to check for dead componets? I have a multimeter.

It's not really an easy task to figure out what might be broke. You could feed it a test tone and try to trace the signal path, but that's for expert schematic readers / troubleshooters (it's a complex circuit). I think the easiest thing to do is power up the circuit and measure voltages. You'll need to download datasheets on all the active devices so you know which pin is which on them. That's where I would start.

[edvard]

I was going to suggest tracing the signal path, but like paul says, that's a bit of a challenge.
Checking voltages may be easier and you can do it with nothing more than your multimeter, but requires more knowledge of the parts involved.

When I'm not in the mood for signal tracing, I go the brute-force route and just replace the most suspect semiconductors.
If I'm not mistaken, the MT-2 uses SIP (Single Inline Package) dual op-amps which may be harder to come by.
Check your local electronics outlets (most major cities still have at least one...) or as a last resort you can get the NJM4558 from Mouser for around 50 cents.

[Paul Marossy]

When I'm not in the mood for signal tracing, I go the brute-force route and just replace the most suspect semiconductors.
If I'm not mistaken, the MT-2 uses SIP (Single Inline Package) dual op-amps which may be harder to come by.

I've done that, too. But only on simple circuits. I believe you are correct about the Metal Zone using those SIP opamps. They are a little harder to obtain than your typical DIP opamp.

[flintstoned]

Smallbear has them. (3) 5218's and (1) 4558. Its the transistors that'll be hard to find.

[Paul Marossy]

Smallbear has them. (3) 5218's and (1) 4558. Its the transistors that'll be hard to find.

Good to know they have those. Yeah, come to think of it, the transistors will be much tougher to round up.

[Chrisq206]

I found a very elaborate dead MT-2 thread between two guys on Bossarea.com. After changing the transistors and doing a few other things his problem was solved when he changed the opamps. I think I'll start there. It seems as likely as anything that someone burned it up w/ the wrong adaptor. Mine had a blown or broken diode next to the adaptor socket.

My next question is, instead of buying the more expensive original opamps ($2 a pop). Could I just  use 45 cent SIP 4558s to see if that's the problem, then decide whether I think it would be worth it to but the $2 ones?

[flintstoned]

Yes, they have the same pinout.

[edvard]

I found a very elaborate dead MT-2 thread between two guys on Bossarea.com. After changing the transistors and doing a few other things his problem was solved when he changed the opamps. I think I'll start there. It seems as likely as anything that someone burned it up w/ the wrong adaptor. Mine had a blown or broken diode next to the adaptor socket.

Many of the transistors are not directly in the signal path and the ones that are may have been somewhat protected by their respective load resistors so that makes some sense.
I've repaired many a gadget, and the op-amps are always the first to go (after voltage-protection diodes, hapless load resistors and obsolete delay chips.)  .

My next question is, instead of buying the more expensive original opamps ($2 a pop). Could I just  use 45 cent SIP 4558s to see if that's the problem, then decide whether I think it would be worth it to but the $2 ones?

At the risk of sounding a heretic, I will reply with a resounding 'Yes'.
Many will tout the benefits of a low-noise or other (usually more expensive) type of op-amp for whatever "mojo" it may impart.
For lower-gain, eq or other tone coloring pedals, I would be inclined to agree, but because of the nature of high-gain distortions, you may or may not notice the difference.
If you're really concerned about it, put a socket where the chips go so you can easily swap out if the 4558's don't cut it for you.
All the schematics I could find of the MT-2 all had 4558's so it'll probably be just fine.

[Chrisq206]

Great info. I guess I just don't want to spend the dough. I got the pedal for ten bucks and a working OD-3 for $30. I took it on because I was curious about the pedal. I wanted to see if I could maybe get some Schenker sounds out of it, but I don't really think ultimately it'll be my kind of distortion. I like high output to wack the input of my amp with not a lot of distortion. If get it to work and It suprises me, I might look into pricey chips for it.

BWT: without having played it in a band the OD-3 sounds amazing right out of the box. 

[edvard]

From my limited experience with a Metal Zone, I can say the tone controls are VERY flexible so dialing in a Schenker tone might be fairly easy with some thought-out twiddling.
On the whole though, it's a fairly high-gain pedal so you'll probably find lower gain settings to be more useful, if you like it at all.
Google around for some soundclips, I know Boss' website has video demos of it as well.

Worst case scenario? It's not an unpopular pedal, so if you don't like it someone else definitely will.
Sell it on ebay or cash it in at your local used music shop.
You'll stand a good chance to get back at least what you spent plus parts...

[Paul Marossy]

From my limited experience with a Metal Zone, I can say the tone controls are VERY flexible

I agree. It's got a bad reputation if you ask me. It works great for singing lead lines the way that I EQ it. I rarely ever use it for chordal stuff, though.