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Thread: Soundcraft GigRac 1000ST, major problems ? blown?

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    Soundcraft GigRac 1000ST, major problems ? blown?

    I am having a problem with the board listed above. Its an 8 channel powered mixer containing 2 internal 500watt amplifiers. When in good working order, the VU meter lights on the right hand side when first powered on, will light up for both the left and right channels all the way to the top, and then drop back to nothing.

    Now the problem I am having is no matter what outlet, or what 110VAC power cable is used, its the same issue. When the amp is I get the VU meter blinks on the right channel rapidly until about halfway up the VU meter (there are 20 total LED lights, 10 per side) to the 5th or 6th light, and then goes to the 4th light, then the 3rd then I get absolutely NOTHING. no sound, no power no meter. the fans do no kick on at ALL like they used to. I used to hear a whirring sound as the amp first kicked on and then it would quiet back down. now I thats all I get. I can if needed take a video and upload to YouTube. Any Ideas? The boards main fuse is good. I have checked it with a meter, and the switch is good, and is reading 110v.

    Thanks so much for any help.

    Mike,

    St. Louis

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    Lifetime Member Enzo's Avatar
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    Vey likely one of the amplifiers is blown, and the unit also probably has a "switching" power supply. The supply shuts itself down the instant it detects the excess load from the blown channel. That would be my guess.

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    how can I be sure of the problem? I went on soundcrafts website, and there was a direct link to look up what power supply unit that you need dependent on your model, and this would SOUND to me like a PSU problem but I was just looking for some other answers. more concrete, or perhaps a way I can check things out.

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    Lifetime Member Enzo's Avatar
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    Yes, it could be the power supply itself at fault. In my experience it is more likely a blown amp channel, but certainly anything is possible. Those modern power supplies have a variety of protection circuits on them, and they tend to shut themselves off when they detect a problem.

    In my shop I would do a quick check for shorted output transistors, and look for some connections to disconect the power amps from the rest of the system.

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    I suppose I will take it into the shop down the road, and hope they don't hose me too badly. I have never used them before.

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    Mike, im not far away from you, Evansville, IN. If you would feel comfortable in shipping it a close distance, I dont charge for estimates. You can verify me if you like. Pro Audio Services I am a service center for several music stores and guitarcenter chain stores in my area. All you would be out is shipping if you need a 2nd opinion. THanks -Eric

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    I may end up doing that. Im going to take it in Wednesday when I get paid, the shop down the street does mostly TV repair but I would assume most PCB and electronics troubleshooting all works out the same way, its a $20 upfront estimate I found out, and then if its not too bad they will apply to my repair. I don't want to spend too much on this as its a backup board for me, and I really havent used it in over a year, its been sitting in the closet, but I am trying to get another PA system up and running so that I can have someone else run karaoke for me and I can make money for owning everything, and its a SUPER easy board to teach someone else how to run.

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    Quote Originally Posted by chipprogr View Post
    Mike, im not far away from you, Evansville, IN. If you would feel comfortable in shipping it a close distance, I dont charge for estimates. You can verify me if you like. Pro Audio Services I am a service center for several music stores and guitarcenter chain stores in my area. All you would be out is shipping if you need a 2nd opinion. THanks -Eric
    Eric, have you seen many of these boards go bad? Being that I am sure Guitar Centers sells A LOT of them?

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    There is alot to be said of a product by how much a technician sees it in the shop for repairs. In over 20 yrs, i have had maybe 3 pieces in the shop from Soundcraft. I own their products and have always been happy with their build quality. Only issue ive ever really had were ribbon replacments on touring boards. Ive never received any soundcraft gear from Guitar Center, nor have i ever seen any to be sent out for repair when im at the stores.

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    man that floors me...this is my 3rd GigRac 1000ST that I have been through. The first 2 were clipping as soon as they were turned on, which I found to happen when there was sound coming into the board and channels being turned on during the "warm up" period. Once I made sure all the channels were turned down and that the mains were turned down, until after I heard the "CLICK" and the fans kick back off, this one lasted quite a while. I just wish I knew what was wrong with this one.

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    UPDATE

    UPDATE

    When I leave the board on, and turn on the phantom power, after a few seconds the light will come on and fade out, and then in a few seconds the light will come on and fade out. There is also a light sound coming from the speaker (i had previously not had one plugged in.) It sounds like i am taking my finger and tapping on the actual paper cone with medium force. I know none of you can fix this via the internet, but after doing hours and hours of research to try to find information, there is basically nothing on this particular powered mixer. Hopefully this thread will be useful to someone else. After I get it back from the shop, I will also post up what the problem is/was.

    Mike

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    Lifetime Member Enzo's Avatar
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    Which is a pretty consistent description of a power supply cycling off and on.

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    Ok, so, I took it into the shop. Guy said 4 of the output transistors on 1 channel are shorted out. Supposed to take between a week and 10 days to get it back. Total price is $188.00 including diagnostic and labor and parts. How fair is this? I would assume thats not too shabby.

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    Quote Originally Posted by Enzo View Post
    Which is a pretty consistent description of a power supply cycling off and on.

    This guy....this guys good...ayyyyyyyy....this guy... thanks

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    For those of you who need parts, or advice Rick @ Harman (soundcraft) is SUPER nice to deal with and works on these all the time. I called him regarding trying to get parts. The output transistors were 20 bucks apiece. The guy at the shop I took it to, found them apparently for 15. So, just to give whoever reads this an idea of what the costs associated are. Rick also said it may be a power supply problem in addition to the transistors, I suppose when the shop replaces them we shall find out and if it is the power supply on that board, I am better off buying a new board, and scrapping this one due to the cost of the digital power supply.

    Mike

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    Lifetime Member Enzo's Avatar
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    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.

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    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.

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    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.

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    Lifetime Member Enzo's Avatar
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    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.

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    Noodle of Reality Steve Conner's Avatar
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    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.

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    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.

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    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..

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    Lifetime Member Enzo's Avatar
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    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.

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    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.

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    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.

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    Quote Originally Posted by Steve Conner View Post
    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.

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    Quote Originally Posted by Enzo View Post
    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.

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