A fellow member of the website Canuck Audio asked me to have a look at this amp, it blew the power fuse along with the 3 amp fuses on the power rails.
I replaced the power fuse and removed the rail fuses and the unit does power up, at least the power supply is okay. Trying fuses in the power rails makes the dim bulb tester light up full brilliance indicating a short. I read a bit about these amps and they seem to burn fuses and output transistors galore.
I tried testing the output transistors in circuit and they seem okay, I will need to remove the whole circuit board, only thing is I need to remove the knobs and I do not have an allen key that fits the small screw.. Are they unique or just British? Anyone know the size, none of mine fit.
Any tricks to check this amp out, it seems well built with good components. Appreciate any help if you have done repairs on this amp.
Thanks Wayne
I replaced the power fuse and removed the rail fuses and the unit does power up, at least the power supply is okay. Trying fuses in the power rails makes the dim bulb tester light up full brilliance indicating a short. I read a bit about these amps and they seem to burn fuses and output transistors galore.
I tried testing the output transistors in circuit and they seem okay, I will need to remove the whole circuit board, only thing is I need to remove the knobs and I do not have an allen key that fits the small screw.. Are they unique or just British? Anyone know the size, none of mine fit.
Any tricks to check this amp out, it seems well built with good components. Appreciate any help if you have done repairs on this amp.
Thanks Wayne
Change C27 470pf. The amplifier is oscillating , the VI limiting is keeping the output devices alive.
What type of capacitor is C 27 470pf.. There is a C127 as well, I presume for the other channel, should that be changed as well or did I read the schematic wrong.. Let me know .. Thanks for the help.. Cheers Wayne
I just started working on this amp and there are no insulators on the outputs. Is this by design or are they missing? I have never seen an amp with this configuration.. Thanks
Is ok just use thermal paste, unless the anodized aluminum is Brocken, check continuity no need for insulators
Thanks for all the replies.. I ordered the parts needed, just one final question, the service manual says to use 16 ohm 5 watt resistors for setting up the output, can I use 8 ohm instead or does it have to be 16 ohm specifically. Will see how it goes and let you know.. Thanks again for the info..
I changed the output transistors and the unit has new fuses all around. I have to do the quiescent adjustment .. The DC offset is low 2.5 mv on one channel and about 20mv on the other AC ripple is negligible. The only issue is the balance seems to be in favor of the left channel, it is not linear in its function, the volume is higher on the left channel, might be because I still have to do the adjustment for the output. I did not change the drivers as they checked okay as far as I can tell. The led was burnt so I changed that for a nice blue one. I have slow blow fuses in the rail lines and will change those for fast blow sometime today when my 16 ohm resistors along with some other parts I ordered show up from Digi key. Repairs are not my strong point in electronics, any ideas are appreciated. Thanks