Ok, if output transistors are blown, don't switch it on again with a fuse F2 anymore after you replace blown transistors. Your voltage amplifier may not work, or deep minus on output of the OpAmp, so thyristor opens and blows up output transistor.
Connect a bulb instead of a fuse F2 and check VCE and VBE on all voltage amp transistors, from Tr1 to Tr7. And voltages on D5,D6 - they may be open.
Connect a bulb instead of a fuse F2 and check VCE and VBE on all voltage amp transistors, from Tr1 to Tr7. And voltages on D5,D6 - they may be open.
Are you still having problems with the 405-2. My first suspicion would be the output triac T2, this can be disconnected by unsoldering the solder link on the pad next to the output terminal on the board. If you can measure D5,6,10,11 &13 in circuit and they are not shorted they are normally OK. If as you say TR9&10 are faulty then you can remove them and power up the amplifier with no load connected and measure the output voltage which should be zero, if it is I would replace TR 9&10 and again with the load disconnected measure the output voltage. If there is a fault you often find that the output voltage is + or – 50V and you can then work back to find out what is forcing the output voltage away from zero, provided you do not attach a load and both TR9&10 are not short circuit you can usually find the fault by measuring the voltages associated with the previous transistors. I have had faulty protection networks N1or N2 and again the amp will work with these removed, hope this helps
Stuart
Stuart
Hi
i have reading the post about 405-2 quad amp
i have a problem
i replace main and driver transistors
i put 2sd424 instead 17556 (strange cos my pcb is 12565 issue 6)
40872 replaced by tip42c
op amp was blown, it cause 14vdc in output, i put a new one and output now is 0v
all electrolithic capacitors they was all fail
, 1 triac of speaker conector pcb, remove triac an amp pcb (i don't have a new one at the moment, but is not blow, just in case)
now it work, fuses does't blow anymore, buuuuut
i have distorsion in one channel (in the repaired channel)
its makes me crazy
r37 and l4 blown, i replace r37 and i put a little copper coil in place of l4
i have suspect of SOA network circuits?? or the l4 coil?
i have checked ALL parts, unsoldered from pcb to be sure
any suggestions?
thanks
i have reading the post about 405-2 quad amp
i have a problem
i replace main and driver transistors
i put 2sd424 instead 17556 (strange cos my pcb is 12565 issue 6)
40872 replaced by tip42c
op amp was blown, it cause 14vdc in output, i put a new one and output now is 0v
all electrolithic capacitors they was all fail
, 1 triac of speaker conector pcb, remove triac an amp pcb (i don't have a new one at the moment, but is not blow, just in case)
now it work, fuses does't blow anymore, buuuuut
i have distorsion in one channel (in the repaired channel)
its makes me crazy
r37 and l4 blown, i replace r37 and i put a little copper coil in place of l4
i have suspect of SOA network circuits?? or the l4 coil?
i have checked ALL parts, unsoldered from pcb to be sure
any suggestions?
thanks
As I know, the 405 consists of two amps:
1) the single ended pure class-A power buffer for low levels with passive resistor load R30/31+Tr7 - no ccs in the neg. half (speakers runs about serial resistor R38, 18-47 ohms)
2) the push pull power class-B buffer - Tr9+Sziklai darl for neg half Tr8/10
By service I check always at first step only the single ended amp for a longer time and in the second step the whole circuit.
1) the single ended pure class-A power buffer for low levels with passive resistor load R30/31+Tr7 - no ccs in the neg. half (speakers runs about serial resistor R38, 18-47 ohms)
2) the push pull power class-B buffer - Tr9+Sziklai darl for neg half Tr8/10
By service I check always at first step only the single ended amp for a longer time and in the second step the whole circuit.
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