need help with my sunn 8520 power mixer

[dkdeleon]

need help!! i am having trouble blowing fuses? I have cheked the transformer among evrything else and i am stummped please can someone lend me hand

[Bill Fitzpatrick]

OK

[Netlist]

We do need more info about the mixer.
I searched but couldn't find anything about it.
Do you have a schematic? What do you mean with 'among everything else'?

/Hugo

[dkdeleon]

Originally posted by Netlist
We do need more info about the mixer.
I searched but couldn't find anything about it.
Do you have a schematic? What do you mean with 'among everything else'?

/Hugo

ok ive done a visual check on the board and see nothing wrong and also checked the transformer it seams to be fine .
by the way its a sunn 8520 powered mixer.
what i did is i checked and found that the reverb springs had broke where the spring meats the grounding rod and replaced {fixed} and replaced a blown fuse then turned it on and still getting blown fuse. hope this helps

[dkdeleon]

Originally posted by Bill Fitzpatrick
OK

by the way thanx for the hand Bill ha ha

[Netlist]

I'm afraid that without a schematic we won't get much further.
Powered mixer? Maybe there's the possibility to detach the power section from the mixing section.
You could measure the output transistors. If one of them has a short the fuse will blow. Does the mixer have two separate amplifiers? One working, the other faulty? Comparing the good one with the bad one can help.
Too many question, again, without a proper plan there's little hope.

/Hugo

[Enzo]

SUnn 8520 is really a Sunn SR8520. It is a powered mixer in head format. 8 channel mixer on front and 520 watt power amp on rear panel.

The preamp won't blow fuses. In order of likelyhood, you have shorted output transistors, shorted rectifiers in power supply, shorted filter cap, shorted power transformer. Visual tests will spot things that burnt up, but most of the time there is no visual indication of failure.

Check the powr transistors for shorts. AN easy method is to measure resistance from the cases of the transistors to the speaker output line. If you have a speaker connected to the output, then just measure to ground. Please make any resistance measurements with power removed. If there is a low resistance from the transistor bodies - the collectors - to ground or speaker output, then they are shorted. Probably only one transistor on positive side and one on negative side. If the base lead shorted, then the whole side is probably shot.

SHorted filters would be extremely rare. Check the four sides of the big bridge rectifier for shorts. WHile you are at it, the four diodes CR22-25 are the low voltage rectifiers, so check for shorted ones there.

If the power transistors and the rectifiers are not shorted, then disconnect the red wires and the blue wires coming from the power transformer. Disconnect them from the main powr amp pc board. Note where they were so you can get them back on right. Make sure they do not touch anything. If the mains fuse still blows, you probably have a bad power tranny.

I would wager on the power transistors though. If there is a shorted one, also check the TO220 types - there are four screwed to the sides of the heatsink.

[dkdeleon]

here are the schematics

[dkdeleon]

Originally posted by Enzo
SUnn 8520 is really a Sunn SR8520. It is a powered mixer in head format. 8 channel mixer on front and 520 watt power amp on rear panel.

The preamp won't blow fuses. In order of likelyhood, you have shorted output transistors, shorted rectifiers in power supply, shorted filter cap, shorted power transformer. Visual tests will spot things that burnt up, but most of the time there is no visual indication of failure.

Check the powr transistors for shorts. AN easy method is to measure resistance from the cases of the transistors to the speaker output line. If you have a speaker connected to the output, then just measure to ground. Please make any resistance measurements with power removed. If there is a low resistance from the transistor bodies - the collectors - to ground or speaker output, then they are shorted. Probably only one transistor on positive side and one on negative side. If the base lead shorted, then the whole side is probably shot.

SHorted filters would be extremely rare. Check the four sides of the big bridge rectifier for shorts. WHile you are at it, the four diodes CR22-25 are the low voltage rectifiers, so check for shorted ones there.

If the power transistors and the rectifiers are not shorted, then disconnect the red wires and the blue wires coming from the power transformer. Disconnect them from the main powr amp pc board. Note where they were so you can get them back on right. Make sure they do not touch anything. If the mains fuse still blows, you probably have a bad power tranny.

I would wager on the power transistors though. If there is a shorted one, also check the TO220 types - there are four screwed to the sides of the heatsink.

do you have a pic of the inside wiring? also where are the power transisters located. "I Know stupid question" It seems to work when i remove the black wire from the transformer? but without out put?

[Enzo]

The schematic, parts layout and parts list is all the technical info there is. I have no pictures. The rear panel of the thing is the power amp. The output transistors are the larger power transistors mounted on the heat sink in there.