Hartke HS 1200 Kick Back bass amp NOT WORKING

[Fabrizio]

Hi ,
I am trying to repair this amp.
The problem is : is not switching on.
NOW: I check the cord, the fuse on the chord,the fuse on the amp. everything OK.
I have my bulb limiter.
I check the continuity and everything is OK.
I detached the wires from the transformer to the main PCB board to isolate transformer to the circuit.
No reading out of the transformer.
I read 250v between the blue and the red going into the transformer.
Is the transformer busted?
Thanks for any input

I put the schematics in the attachmentsamson hs1200 sch.pdf

[The Dude]

Check continuity across the tranformer primary with no power applied (your blue and red wires). If you get an infinite reading, the transformer primary is likely open.

[Fabrizio]

on the transformer I get 5.4 between the red and blue wires and buzzing from the multimeter.

[The Dude]

...and that is the same place you read 250VAC? If that is so, connect the primary back to the amp and apply power. Leave the secondary disconnected. What VAC do you get across each of the secondary windings labeled SEC1 (red to red) and SEC2 (blue to blue)?

Edit: "buzzing from the multimeter"? You did remove power first?

[Fabrizio]

Hi Dude!
For buzzing I mean the continuity test(the sound that there is continuity....sorry for confusion)with power off.
I did switch the power on(I have my poor mans Variac) and on SEC1 I couldn't read any voltage between Yellow and red1 ,Yellow and red2.

[The Dude]

Sorry for what might seem a dumb question, but I have no idea of your experience level. You are measuring for AC voltage?
Also, do you get anything across SEC2 or no voltage across either secondary tap?

[Fabrizio]

No worries for Dumb Questions, I measure DC on the output of the transformer. AC on the input.
Now I saw that one of the blades was a bit loose(the one for the brown cable BR on the schematics). I resolder it but... OUcchh Lamp limiter kiks in now. so there is a short somewhere I presume

[The Dude]

The transformer output will be AC- not DC. The job of a transformer is only to provide isolation and, in most cases, step the voltage up or down. The exception is a 1:1 transformer used for isolation. It is the rectifiers and filter caps that convert that AC to DC voltage.

[Fabrizio]

ouch, so it is ac to ac transformer? I assumed it was ac to dc . My bad then... Now the problem that I have is a short circuit somewhere
Of course after the rectifiers is DC ...

[The Dude]

The most likely culprit is one or more shorted output transistors. Check them for shorts. Note that they are paralleled. If one is shorted, they all appear to be shorted. If you find a short there, you will need to remove them and test out of circuit to see which of them is actually shorted.

Edit: The above is if you do indeed have a short. However, in post one you said the fuses were good. A short would likely cause a fuse to blow. How bright is your bulb limiter? I'm wondering if the "brown cable" connection problem you found was the only problem and the brightness of your bulb is normal. It would still be a good idea to check for shorts before removing the bulb limiter.

[Fabrizio]

Hi Dude, I haven't connected the transformer to the PCB board Yet . RC1 and RC2 are not connected yet

[The Dude]

Oh. I thought you were connected. So the bulb is glowing bright even with the secondary disconnected? Measure the AC voltages out of the 2 secondary windings and post them.

[The Dude]

I should add. Be careful in there. We don't want to read about you in the obituaries.

[Fabrizio]

I am still alive like Bee Gees

I should add. Be careful in there. We don't want to read about you in the obituaries.

Hi Dude, sorry for late reply but I went to bed(I am in LOndon so we have different time). Thanks for your help.
The Light bulb is coming on very bright.
At the beginning it wasn't because there was a broken trace between the brown and red cable blades.
Now that I soldered the two, it is showing a short(a very bright light bulb).
Rc1 and Rc2 are disconnected from PCB board.
I can't measure the AC voltage out of RC1 and RC2 as I see the light bulb(very bright) coming up and I switch off immediately.
Am I missing something?
No worries Dude I am careful there ( I know its 250 V AC )
I should add I am no expert but I did open up quite a few amps in the past.
I am looking for some good advice from people that are more experienced than me and I am really grateful for any input given .

[The Dude]

This isn't making much sense. No fuses were blown indicating that there wasn't a short anywhere. Yet, with the transformer secondary disconnected, you say the bulb is glowing brightly indicating a short. Please check that all of the fuses are the correct value. Maybe someone stuck a highly overrated fuse in the unit? Also check the transformer for windings that are shorted to each other or the transformer housing.