This is the meter i will be using

 

Did this happen with the lamp in series with the mains supply to the amplifier ? (As this is a 500 watt amplifier you may need to use a higher wattage lamp as the magnetizing current for the transformer may be enough to light a 100 watt lamp. You will probably have to put lamps in parallel to get a higher wattage rating.) The red fault light is lit due to the loss of +45 to that channel due to the blown fuse. The most common failure mode for for transistors in the part of the circuit is a collector to emitter dead short. (If there has been a very high fault current then the internal connections to the collector or emitter can fuse open circuit.)

Les.

 

Hi no, i dont have the lamp in the AC input yet, this is direct into the wall, i have the bulb holder and a switch but need to find a socket for the amp to plug into at the end,

Also its not so easy to find an old type filament bulb these days, there almost all LED

 

The house lamp wiring that Delta posted looks good. Make sure that the switch and lamp is placed on the AC LINE (live) wiring.
In the US, 120V AC live wire is usually coloured black. In the UK, 230V AC live is brown.

 

I made a point of keeping my stock of filament lamps when CFL lamps started to replace them. I don't think 50 W halogen GU10s would be as good for this purpose as they have a very low cold resistance. Without something to limit the current you will keep blowing fuses and transistors without being able to take measurements to trace the faults.

Les.

 

The house lamp wiring that Delta posted looks good. Make sure that the switch and lamp is placed on the AC LINE (live) wiring.
In the US, 120V AC live wire is usually coloured black. In the UK, 230V AC live is brown.

View attachment 228873

Thank you for that, i assumed it would be on the live

 

Will this work ? , its the closest thing i have

 

You are welcome. We just want to make certain that you do everything right.

While waiting for a proper house lamp, does the amp power up without blowing any fuses?
Have you confirmed that both +ve and -ve rails are present, though showing high readings?

Edit: You can try the 40W bulb. What we want to see is how bright the bulb glows.
It should come on bright initially on start up then should glow dim afterwards.

 

BTW, in open forums such as this, it is unavoidable that many helpers would like to chip in. That's in our nature. That can make it confusing for you if you are being instructed from different directions. Sometimes others can shine a different light on the situation.

It is probably best for one person to take the lead and others should provide input only when necessary. I would be happy to take a back seat if someone else wants to lead the way.

One thing we need to check is if the fault light is truly indicating a fault or is the fault light faulty.

 

Ok if i remove the +45v supplt to the right chanel all fault lights go out and no fuses are blown, also noticed a dead short across Q26 collector and base, however if i remove the nuts connecting Q28 base so the base is not connected to the board Q26 short goes away, both components seem to test correct out of circuit, also if the -45v supply to chanel 2 is removed and the +45v left connected it still blows fuse 2, this leads me to believe the problem is in the top half of the schematic, does this sound right ?

Cheers

 

Turns out Q28 has blown its magic smoke , i do have the old one that tests good, i replaced all to be semetrical and to try make each chanel as close to each other as possible

 

Ok, replaced Q28 with the old good one, now it powers up with no fault LED,s at all, however F2 LED is on dimm but not blowing the resistor, think i am at the end of my knowlage now lol

 

Thanks for the update. We are not ignoring you. It just takes time to digest the information, study the schematics and run some simulation, besides doing some chores while enjoying the day.

When you say "top half of the schematics" it would be better to identify some transistors such as Q5 in the POWER AMPLIFIER LEFT CHANNEL. There are numerous pages of schematics.

 

Ok if i remove the +45v supplt to the right chanel all fault lights go out and no fuses are blown, also noticed a dead short across Q26 collector and base, however if i remove the nuts connecting Q28 base so the base is not connected to the board Q26 short goes away, both components seem to test correct out of circuit, also if the -45v supply to chanel 2 is removed and the +45v left connected it still blows fuse 2, this leads me to believe the problem is in the top half of the schematic, does this sound right ?

Cheers

This is all in the Power amplifier right chanel

 

Are the power transistors in the power output stage soldered in or are they in sockets?
If they are socketed then you should remove all four transistors in the RIGHT CHANNEL.
Make sure that you label where each transistor belongs.

 

Hi, they are soldered in, i can remove them if you like, i know where each one goes

 

And are you refering to Q28, 36, Q26 and Q34, there are another 2 on the schematic that are not fitted

 

Ok. Remove Q28.

Let me know what transistors and all other components that are not installed.

If the amp powers up without blowing fuses measure all four power supply lines and voltage at speaker output (no speakers attached).

Make all measurements with the BLACK meter lead to 0V reference.
Pay attention to the +/- polarity indicated on the voltmeter. This is essential.

+45V
-45V
+55V
-55V

LEFT Channel speaker output
RIGHT Channel speaker output

 

When i said not fitted, i mean the amp came from the factory like that, so right chanel Q17 and Q19 were never fitted, the same for the left chanel, also PR1 and PR2 were never fitted,
Here my test results you requested:
Measuring with black probe on T26 as 0V
And Q28 removed,

R/C +45v= 64.67vdc
R/R -45v= --64.57vdc
R/C +55v= 77.02vdc
R/C --55v= --76.46vdc

L/C +45v= 64.67vdc
L/C --45v= --64.63vdc
L/C+55v= 77.33vdc
L/C--55v= --77.31vdc

R/C output + T9= 0.005mvdc
R/C output -- T10= 15.10mvdc

L/C output + T4= 0.007mvdc
L/C output-- T5= --10.76mvdc

 

T4 and T9 are the amplifiers ground line. (Marked 0vP) The outputs T5 and T10 seem reasonable.
If you look at the schematic you will notice that The missing components are marked "N.F." (Not fitted.) These are probably fitted in a higher power version of the amplifier.
For the right hand amplifier if you connect the negative of a 1.5 volts cell (AA or AAA) to the 0vP rail and the positive to In - R (The junction of R77 an R69) via a 1.8 or 2.2K resistor I would expect the output of the amplifier to read about -4.5 volts.
The same should happen if this is done to the corresponding points on the left hand channel. If the polaritu of the 1.5 volt cell is reversed the output should go to about +4.5 volts.

Les.