Soundcraft GigRac 1000ST, major problems ? blown?

[Enzo]

One step at a time. The power suply could be damaged or it could be just fine. it really is capable of protecting itself fairly well. Your tech could disconnect the blown power amp stage and fire up the unit without it. That would tell you if the power supply was OK or not.

[phlash]

Got the amp back today. Turned it on, played through it, at half volume on the main, and half on the channel not even very loud, was listening to a song with a soft intro (just piano and vocals) and heavier verse, and as soon as the verse came in(drums bass and guitars) i heard a loud POP. and it wouldnt power back up. So.....I took it back in, and dropped it off.

[phlash]

Got it back. Played through it for 15 minutes. Blew up again. Opened the case, The "experienced technician" used 2 different brands of output transistors, and didn't even use the correct ones to begin with. He used MJ15025 and MJ15024, when the factory parts are MJ15025G and MJ15024G, 2 with dome tops and 2 with flat tops. The amp came originally with flat top output transistors. I don't know how much difference the "G" makes, or the bubbled top, but, I can't keep it working. He told me when I picked it up he couldn't warranty it and keep working on it. I think trying to get my money back is going to be fun.

[Enzo]

The G and non-G are interchangable. G stands for "green" as in eco-friendly. It is the Moto/OnSemi abbreviation for lead free - it meets the RoHS standards. The difference between the two is mostly that the pins sticking out the bottom are no longer tinned with lead solder.

The differences in shape are just production runs.

That difference should not blow up the amp. Even cheap crummy PA amps are not usually THAT sensitive to the transistors used. And unless you CRANKED the beJesus out of it, I doubt that much stress was put on them.

Now it is possible the guy was sold fake transistors. That is a huge industry problem. The only way to tell is to hack open the transistors themselves and see if the silicon inside is robust.

And it is also possible the repair was not 100%. Did your guy ever get a schematic? I can usually repair amps without them, but it is harder, and especially harder to check teh various protection circuits.

It pays to shop around, as it turns out, I am placing a parts order right now, and MJ15024 and MJ15025 are on the list. I usually buy them from Allied, who wants $7.17, and $6.09 today. But the same parts from Mouser are selling for $3.83 and $3.63. If that shop paid $7 for one, then I can see charging $15, but usually I expect to pay about $4 each, and I sell them for about $7-8.

[Steve Conner]

I could be wrong, but I don't think real MJ15024/5 have dome tops. I only have a few old Motorola ones around here, but they all have flat tops. Enzo, have you ever seen any with dome tops?

Post some pics of the transistors if you can.

The "G" isn't a problem, but mixing different transistors in one bank is.

If you've blown 3 of these powered mixers... What speaker load impedance are you using them with? Maybe you have some 2.7 ohm killer speakers, or maybe your line voltage is 195 volts or something.

[phlash]

no, he did not have a schematic. I offered him one, and he got pissy with me, and took it as an insinuation he didn't know what he was doing.

[chipprogr]

Sounds like fake transistors that MCM electronics has been selling. I stopped buying transistors from them awhile back. There were the M-Mj15024 (ON-Semi originals) and then the MJ15024's that MCM house branded i guess. Had a peavey CS800 that would burnup within a few seconds to minutes of operation and it was ALWAYS one of the new parts from them. Mouser seems to be a good source, i use to buy in bulk from Future Active Electroncis.

Sorry your having this issue...wow..

[Enzo]

They haven't been making anything I buy with the domed tops for a while, but the MJ15024 has been around a long time, who knows how old they are. Well, I guess the date code on the part would tell.

I don't think about it, but I don;t recall anything but flat tops for some time on any Moto TO3s.

Just checked MCM. Wow,I have never seen generic MJ15024s. Real ones are cheaper than those at Mouser. I never got fakes at Mouser or Allied on the Moto parts. The MCM part has a "review" space. if you got fakes that burnt up, write a review there and tell the tale. Would you buy a transistor from them with a review on the page comlaining they were fakes? I wouldn;t.


Let me get this straight. I fixed it, but I won;t warrant my work, and I don;t want to see a schematic. Interesting business approach.

[chipprogr]

I "voted with my feet" as they say and just stopped purchasing from them. I read later that MCM , although being an ON-Semi authorized distributor, got in trouble for selling fakes. It is interesting, ive never seen a generic MJ1502x series transistor from anywhere but MCM. type in " M-Mj15024 " and you get the Original motorola part. Type in just MJ15024 and you get a "distributed by MCM" part. order them and you'll see they are not moto parts. They also dont hold up either.

I warranty everything i do, if i screw it up, i have to eat it and give back the customers money. Thats just bad business.

[phlash]

yeah, that was his exact approach... Such a douche...I took the PA to a very reputable shop that deals only in pro audio repair. From the moment I walked in, it was night and day from shop #1. Shop #2 was Professional and HELPFUL, and knowledgeable attitude. I told him the parts the the first guy replaced, and he took me in the back room and pulled the exact part out of a random drawer that wasn't labeled and then showed me around on what they worked on, and this and that. Very much an entirely better experience so far. Its a 3 week lead time, but that should be up very very soon. I am assuming whence I get my equipment back from the reputable shop I will have more than just a blown final output transistor. I was told that I will be given not only a written statement of what was done, but also a baggie of whatever old parts they replaced.

I ended up having to have my bank return my funds for 'services not as advertised' he has 90 days or something like that to overturn it.

Also, I think the "dome top" was the 2 outputs that were shorted out? does that sound normal? (shop number 1 replaced 4 of them, but only 2 were domed making me think those were the ones shorted) He also left flux ALL over the board, and didn't make even an attempt to clean it.

[phlash]

I could be wrong, but I don't think real MJ15024/5 have dome tops. I only have a few old Motorola ones around here, but they all have flat tops. Enzo, have you ever seen any with dome tops?

Post some pics of the transistors if you can.

The "G" isn't a problem, but mixing different transistors in one bank is.

If you've blown 3 of these powered mixers... What speaker load impedance are you using them with? Maybe you have some 2.7 ohm killer speakers, or maybe your line voltage is 195 volts or something.

Nah, they have blown in different ways in different locations. I measured the speakers with a meter and was reading 7.2ohms. Line voltage was 114V. I use the same speakers and same cables with 2 other powered amplifiers (one peavey and one behringer). I think these may just be crappy or have a small fault. Its not like I am driving the hell out of it either. I don't let them clip. Been running live sound for around 9 years now, with no other problems.

[jonno1812]

One step at a time. The power suply could be damaged or it could be just fine. it really is capable of protecting itself fairly well. Your tech could disconnect the blown power amp stage and fire up the unit without it. That would tell you if the power supply was OK or not.

Mine messed up last week, amp 1 faintly lit up, upon power off both lit up. Turned all knobs down and had a mess, it popped and came back to life. Played music for about half hour to test it. Turned back on today and start playing music to hear a hissing sound and then pop, amp buttons lit up again really getting stressed with it.