Eti-480 100w Amp Help Please

[jacquesl]

i'm not so good in my english.

I have a probleme with this amp ETI-480 100W

in my pic is some detail

the under side of the board looks bad that the flux from the soldering none of that lines

are shorting. I'm 100% sure.

The probleme is with the finishing part the 100 ohm resistors it's getting F... hot and starts smoking.

and i can find the fault.

i had built 5 of them all the same problem just this one are going to use external

transistors with wires conected to the board from the heatsink

becuase if got a space problem in a box.

please help anyone ???

 

[Netlist]

I found a schematic here but couldn't find the 100 ohm resistors. Are we talking about the same amp?
Aren't they supposed to be fuses?

/Hugo

 

[jacquesl]

yes it's the same project ETI-480

a family member give me the plans to built it he built like 10 of them and if worked for him.

but i built 4 and none work

so i'm pissed off and sitting with a bured finger from a 100 Ohm resistors

 

[Tube_Dude]

Hi Jacquesl

There is a fatal mistake in the schematic and in your pics, the power supply , must be connected to the power transistors side of the PCB .

Is the current that goes to the output stage , that burn the 100 ohms resistor...

This one is to easy...

Regards

 

[audioPT]

Hi Jacquesl

There is a fatal mistake in the schematic and in your pics, the power supply , must be connected to the power transistors side of the PCB .

Is the current that goes to the output stage , that burn the 100 ohms resistor...

This one is to easy...

Regards

Connect the power to the other side of the resistors

I've got the same problem... But I figured it out before puting some power on it

Olá t_dude

 

[jacquesl]

Here are my 4 amps none of them work

problem

100 ohm resistors burn out

The voltages are +- 30 volt over the 100ohm resistors

If I put the all two fuses in R15 burn out

but if i take R14 and R18 out the 100 ohms dont get hot.

so if anyone also had the same problem please post a reply

 

[jacquesl]

Here are all 4 amps from me

 

[jacquesl]

Tube_Dude if I do that thing you told me R18 burns and Q8 get helll got but the 100 Ohm resistors dont burn out

 

[Frank Berry]

Here are my 4 amps none of them work

problem

100 ohm resistors burn out

The voltages are +- 30 volt over the 100ohm resistors

If I put the all two fuses in R15 burn out

but if i take R14 and R18 out the 100 ohms dont get hot.

so if anyone also had the same problem please post a reply

Make sure all transistors are installed correctly then measure the junctions of all transistors.
If all of your amplifiers are doing the same thing, you have made an error somewhere. You've probably made the same error on all amplifiers.
Before going any further, replace the 100 ohm resistors with fuses and then power the circuitboards through current limiting resistors. Insert the resistors at the point where your + 30 and - 30 volts connect. You might even use a couple of low wattage light bulbs rather than current limiting resistors. That will give you a visual indication of an over-current situation.

Good luck and report back with your results.

 

[jacquesl]

Tube_Dude

If I do that thing with another amp R17 burn out but the 100 Ohm resistors dont burn out.

but anyway if that worked as soon if i going to put that fuses in there will be smoke.

so that dont work.

 

[jacquesl]

I have tested for shorts where the transistors meets the heatsink with a ohms meter ans a bizzer with battery.

 

[Frank Berry]

Check that your other transistors are installed correctly. They may be installed backwards.

 

[jacquesl]

Frank, you must look at my pictures at the transistors

I''m doing that light bulp thing right now

 

[audioPT]

Read this post.

Maybe it helps

 

[jacquesl]

I'v already readed that one it but his probleme is fink is a short on his power transistors at the heatsink.

I already readed that one

 

[Tube_Dude]

Is the overall feedback connected ? (R8 to output ).

And I hope ,you are working with the output transistors in circuit?

 

[jacquesl]

Yes R8 is connected to the output

 

[Frank Berry]

Again. Check the orientation of all transistors. Since all amplifiers are exhibiting the same failure mode, it's likely that you have made the same mistake on all PCB's.

Don't panic. Double check your boards before powering them up.

Relax. You'll find the problem.

 

[jacquesl]

frank, if you seeing the problem please tell me becuase i give up.

this is my 10th day of crap with this amp.
I'm going to unicom monday to a tv repair dude and ask him if he can help me.

the resone i built this amp is that someone give me a marantz amp that dont work, so i finded the fault, its the power amp section the rest work thank god.

model 1060

its has crappy old confusing parts in but if mastered it after 2 hours

 

[Tube_Dude]

The drivers transistors Q7 and Q 8 don't look well connected.

The pinout viewing from the frot of the transistor is:

BD139
----------
E C B

Have a look!