im a long time lurker that usually fixes stuff by actually looking crap up. but im kinda stumped. and i don't have much knowledge in this amp.
first off i bought this off craigslist met the guy said he thought it works well it didnt. i offered him 20.00 for it and got it.
so it turns on in protect mode
ive removed the output transistors ( pian in the butt with my cheap bulb type desoldering iron )
and i checked each one applying voltage and a led and uaed a 9v battery to open and close the gate. all 12 checked out good.
i keep reading about a u21 being the culprit i cant see it anywhere.
im dead set on fixing this amp. ive built and modified tube amps so im not a complete noob to electronics.
also cant seem to find a schematic.
power supply is right at 100V but the caps are 100v rated seems odd but other threads seem to say thats ok.
please help i wont wast your time. Thanks
first off i bought this off craigslist met the guy said he thought it works well it didnt. i offered him 20.00 for it and got it.
so it turns on in protect mode
ive removed the output transistors ( pian in the butt with my cheap bulb type desoldering iron )
and i checked each one applying voltage and a led and uaed a 9v battery to open and close the gate. all 12 checked out good.
i keep reading about a u21 being the culprit i cant see it anywhere.
im dead set on fixing this amp. ive built and modified tube amps so im not a complete noob to electronics.
also cant seem to find a schematic.
power supply is right at 100V but the caps are 100v rated seems odd but other threads seem to say thats ok.
please help i wont wast your time. Thanks
I believe if you email Rockford they will send schematics for out of production amps. Also Perry Babin might have one, or something similar.
Does the amp still protect with all output transistors removed?
Does the amp still protect with all output transistors removed?
Look closely and you will find U21, when you do post the DC voltage on all of the pins.
Is there any DC on the + output terminal?
Does the amp draw current?
Is there any DC on the + output terminal?
Does the amp draw current?
If pin 6 of U21 is negative, it's definitely defective. If it tries to charge towards 5v but stops below 5v, that could also indicate that it's defective.
fosgate
Its still is in protect with all transistors removed.
I will look for this U21 and report my findings.
Its still is in protect with all transistors removed.
I will look for this U21 and report my findings.
U21 results
1 -8.50
2. 8.13
3. -8.96
4. 9.82
5. 5.03
6. -6.79
7. 8.69
8. 10.02
1.9millivolt on speaker output
Not sure on current draw I'm using a 12v. 19amp computer power supply to power it up at 12.09vdc
1 -8.50
2. 8.13
3. -8.96
4. 9.82
5. 5.03
6. -6.79
7. 8.69
8. 10.02
1.9millivolt on speaker output
Not sure on current draw I'm using a 12v. 19amp computer power supply to power it up at 12.09vdc
Cool thanks guys. I'll try get one locally if not I guess mouser. Radio shack is a joke they should be cell phone shack. They never got anything I'm interested in.
Once I get it I'll report back.
Also what adhesive do I use to attach the thermocouple on the the output transistor strip?
Once I get it I'll report back.
Also what adhesive do I use to attach the thermocouple on the the output transistor strip?
If you're referring to the small thermistor that's essentially an epoxy blob on the end of two wires, it's simply pressed into the heatsink compound that's displaced through a hole in the MEHSA insulator.
The old heatsink compound has to be completely removed and replaced.
If one of the thermistors has a ring terminal and had a lockwasher under it originally, you must reinstall that lockwasher between the thermistor and the MEHSA insulator.
The old heatsink compound has to be completely removed and replaced.
If one of the thermistors has a ring terminal and had a lockwasher under it originally, you must reinstall that lockwasher between the thermistor and the MEHSA insulator.
OK so I replace the U21 and the protect light turns off as it should.
So I resolder the outputs turn It on and 2 output transistors explode with a flash!
At the same time the RF logo led got dim and the remaining outputs got kinda hot.
So I removed the outputs and the RF logo led is bright again and the protect light works as it should.
So what else is blow? Or needs checking on?
So I resolder the outputs turn It on and 2 output transistors explode with a flash!
At the same time the RF logo led got dim and the remaining outputs got kinda hot.
So I removed the outputs and the RF logo led is bright again and the protect light works as it should.
So what else is blow? Or needs checking on?
The outputs are in two groups of 6. All 6 in the group where two failed must be replaced.
Some of the drive components and gate resistors may have failed as well.
Do you have a scope?
Have you ever replaced transistors soldered to the MEHSA insulators?
Some of the drive components and gate resistors may have failed as well.
Do you have a scope?
Have you ever replaced transistors soldered to the MEHSA insulators?
it was one of each type output that blew.
i do have a 100mhz scope im slow but have the basics in using it. and a good digital frenquency generator.
ive seen youtube videos on how to remove the MEHSA board.
im totally up for suggestions. i have a nice digital weller soldering station also a couple heat guns ones 140 watt max and the other is 200 watt max.
im all ears for methods on fixing this. its a learning expierence for me. i appreciate everyones time in this matter.
i do have a 100mhz scope im slow but have the basics in using it. and a good digital frenquency generator.
ive seen youtube videos on how to remove the MEHSA board.
im totally up for suggestions. i have a nice digital weller soldering station also a couple heat guns ones 140 watt max and the other is 200 watt max.
im all ears for methods on fixing this. its a learning expierence for me. i appreciate everyones time in this matter.
Read the oscilloscope page (page 73) of the car audio site (link in sig file below). Pay special attention to the 'best initial settings' section.
Remove all of the output transistors. For the ones that have to be replaced, cut the legs free and heat each leg to remove it.
I don't know what you read on youtube but most of the technical vids I've seen were wrong. The following is for the larger transistors but it's useful for the small transistors as well.
http://www.diyaudio.com/forums/car-...-schematics-3.html?postid=1901581#post1901581
Do you think you possibly pulled any of the vias for the output transistors when you initially removed them?
Remove all of the output transistors. For the ones that have to be replaced, cut the legs free and heat each leg to remove it.
I don't know what you read on youtube but most of the technical vids I've seen were wrong. The following is for the larger transistors but it's useful for the small transistors as well.
http://www.diyaudio.com/forums/car-...-schematics-3.html?postid=1901581#post1901581
Do you think you possibly pulled any of the vias for the output transistors when you initially removed them?
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