SVT -5 Pro

[Amp Kat]

Hey fellows it's been awhile since I posted and building a website and doing Studio time has been extremely time consuming so sorry bout that. I got a SVT from a Studio Musician and had a few questions regarding schematics and repair. 1st off the schematics I found on the net show two channels with ( 8 )IRF 240 mosfets and these do have those however I only have 5 per channel for a total of 10 not 8 per channel as the schematic shows and they are originals with the red dots and blue dots on respective channels. Enzo had given me schematics for some SVT's but those weren't in there but I did use all of the others on other amps so that was a huge help as always from him.

The problem with the amp is no power output however the rail voltages for the power section are there and all of the fets are showing good on the meter and all of the 47 ohm resistors are good. No DC on the output jacks A & B in stereo mode however I do get a hum from the speaker outs when I hook up my test speaker. It's on both channels and the switch is set to stereo mode. I did find that the screw on the 1st Mosfet on the blue channel is not grounded and all the others are. Not sure if that is just a design flaw or something open but I really don't want to take this board off if I don't have to iykwim.

Preamp out works however I can't get the overdrive to work. It switches on and the led shows on but I get no output or mixing from it when turned on so I'll troubleshoot that next. Just wondering if you guys have seen this problem or would help me get it back right. I don't think it has a major prob so could be something simple as owner said he cleaned it and put it back and it didn't work. TIA

KB

[nosaj]

Hey fellows it's been awhile since I posted and building a website and doing Studio time has been extremely time consuming so sorry bout that. I got a SVT from a Studio Musician and had a few questions regarding schematics and repair. 1st off the schematics I found on the net show two channels with ( 8 )IRF 240 mosfets and these do have those however I only have 5 per channel for a total of 10 not 8 per channel as the schematic shows and they are originals with the red dots and blue dots on respective channels. Enzo had given me schematics for some SVT's but those weren't in there but I did use all of the others on other amps so that was a huge help as always from him.

The problem with the amp is no power output however the rail voltages for the power section are there and all of the fets are showing good on the meter and all of the 47 ohm resistors are good. No DC on the output jacks A & B in stereo mode however I do get a hum from the speaker outs when I hook up my test speaker. It's on both channels and the switch is set to stereo mode. I did find that the screw on the 1st Mosfet on the blue channel is not grounded and all the others are. Not sure if that is just a design flaw or something open but I really don't want to take this board off if I don't have to iykwim.

Preamp out works however I can't get the overdrive to work. It switches on and the led shows on but I get no output or mixing from it when turned on so I'll troubleshoot that next. Just wondering if you guys have seen this problem or would help me get it back right. I don't think it has a major prob so could be something simple as owner said he cleaned it and put it back and it didn't work. TIA

KB

Contact ampeg they or Hard industries will give you a schematic after an NDA form.

nosaj

[Amp Kat]

Is that Loud Technogies or did they change ?


UPDATE : Found a screw in it and still has hum so not sure what it took out but obvious culprit.

[nosaj]

Is that Loud Technogies or did they change ?


UPDATE : Found a screw in it and still has hum so not sure what it took out but obvious culprit.

It's Loud not sure what i was thinking. Any idea where the screw came from?
nosaj

[Amp Kat]

Yes the preamp mounting board and it's back now where it should be.

[Jazz P Bass]

The schematic can be found here: Ampeg SVT-5 PRO Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

6 Mb.

[Enzo]

http://bmamps.com/Schematics/ampeg/A...Schematics.pdf

That is the power amp with both 8 and 10 transistor schematics included. Scroll down to the second set for the 10 version.


Long time, KB, god to hear from you.

[Amp Kat]

Thanks Enzo, been real busy in the past so thanks for the Schemos fellows andI'll get back soon.

KB

[Amp Kat]

Ok so let me ask a question. I'm only seeing 10 Mosfets on the top and schematic showing 20 so are the others on the bottom of the heatsink or mounted to the mainboard. ? Either way the only way to check them is to remove that assembly ?

[Amp Kat]

Soooo now I've got this thing totally apart and thinking now that maybe I do have some bad MOSFET's as I lifted some resistors to check the string and found few shorted ones. I didn't realize the relay would not pass DC offset to the speaker outs but that's why there was no DC.

So can anyone point me to somewhere other than Loud and if I buy some from say Mouser or MCM would they be matched. I read a thread from Ampage where Glen from Mars was saying they need to be matched and these have red dots and blue dots respectively so just wondering where you guys are getting these from these days. Loud is not taking calls and is pretty much useless as we speak.