My amp recently blew FS2 and I'm now reading 50v DC across the fuse holder. I've checked all the resistor values, checked TR1, TR3, TR4. I've replace blown TR10 and checked all other transistors. I've replaced C10, C19, C18 and C17 as a matter of course as I'd already bought the components to upgrade the amp. I'm still getting 50V at the fuse holder, any ideas please?
Thanks
Peter
Thanks
Peter
The circuit diagram is at the following link. http://www.dc-daylight.ltd.uk/Valve-Audio-Interest/Schematics/QUAD-405-Evolution.pdf I haven't copied it in case of copyright. My boards are M12565 issue 6. which is page seven of the diagrams.
Thanks
Peter
Thanks
Peter
Hi,
assemble a mains light bulb into a wander lead. The light bulb is wired in series with the LIVE wire only.
It will allow you to plug in the faulty amp without the risk of blowing the whole thing up.
When operating normally the bulb flashes briefly at switch on and then either goes off or glows very dimly.
If it glows bright and you are using an amp with a very high quiescent dissipation then choose a higher wattage bulb (40W to 150W).
If the amp is faulty and tries to draw too much current, the bulb lights up normally and the amp sees only a few volts across the mains transformer. This can allow some measurements to be taken to help locate the fault.
Power dissipation with the bulb inline is very low and nothing gets hot, although some components might just get warm.
assemble a mains light bulb into a wander lead. The light bulb is wired in series with the LIVE wire only.
It will allow you to plug in the faulty amp without the risk of blowing the whole thing up.
When operating normally the bulb flashes briefly at switch on and then either goes off or glows very dimly.
If it glows bright and you are using an amp with a very high quiescent dissipation then choose a higher wattage bulb (40W to 150W).
If the amp is faulty and tries to draw too much current, the bulb lights up normally and the amp sees only a few volts across the mains transformer. This can allow some measurements to be taken to help locate the fault.
Power dissipation with the bulb inline is very low and nothing gets hot, although some components might just get warm.
I have had a faulty SOA circuit fail on several 405-2s These are shown as N1 & N2. These are mounted on 2 small 5 pin pcb/modules. To check you can remove these and the amplifier will operate with out them fitted but will not be protected against over current so do not connect a load to the output.
Stuart
Stuart
Now please stop blowing fuses, connect a light bulb accross F2, and switch on your amp.
See what is a voltage across collector - emitter of tr10, base - emitter of tr10, collector - emitter of tr8 and base - emitter of tr8.
Also, gentlemen who criticized Swinik, please show me your "Bridge" on the schematics. The whole patented "invention" is an approximation of a transfer function through the R38 resistor. It reminds me another patent, for the invention of the weapon with a screw-like trunk.
See what is a voltage across collector - emitter of tr10, base - emitter of tr10, collector - emitter of tr8 and base - emitter of tr8.
Also, gentlemen who criticized Swinik, please show me your "Bridge" on the schematics. The whole patented "invention" is an approximation of a transfer function through the R38 resistor. It reminds me another patent, for the invention of the weapon with a screw-like trunk.
pborlace said:
I mean, check if they are alive and not shorted.
Unplug your amp, let it stay few minutes untill all capacitors are discharged, then check everything going from the F2 fuse, step by step, unsoldering and checking resistance to the ground with a speaker connected, probably D11 is bad, or emitter of tr10 is shorted to the heatsink.
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