Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
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Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
I agreed (reluctantly) to take a look at my buddy's circa-'89 Fender Super 60 red knob era amp. I guess this amp was their attempt to compete with Mesa-Boogie. Its a fixed bias amp (with no bias control adjustment!) with 2 6L6gc's and Bassman-looking iron in a Princeton-sized cab. I replaced the fuse a couple of times and tried switching on the amp with the power tubes both in and out. The amp comes on with a new fuse, but as soon as I bring it off standby the fuse blows, even with the power tubes out. Any clues about where to start? Getting the PCB out of this thing is a B@#ch! The PCB is put in components down and I tested the power resistors and screen grid resistors from the back-side of the PCB.
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
http://ampwares.com/schematics/super_60_rack.pdf
Is the blowing fuse "F4", the HT fuse ?
I'd be looking first at the bridge rectifier, and then the flyback snubber diodes (on the power tube plates).
rd
Is the blowing fuse "F4", the HT fuse ?
I'd be looking first at the bridge rectifier, and then the flyback snubber diodes (on the power tube plates).
rd
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Thanks for the reply. It is blowing F1, the 2.5A fuse on the mains and the only one accessible from outside the amp.
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
The schematic indicates F4 may not be present on all versions.Matt D wrote:Thanks for the reply. It is blowing F1, the 2.5A fuse on the mains and the only one accessible from outside the amp.
In which case the mains fuse would blow if any of those diodes shorted.
(typical diode failure mode is a short)
rd
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Cool. I'll open it up tomorrow and test the diodes for shorts.
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
http://el34world.com/charts/Schematics/ ... _60All.PDF
Here is a parts list and layout as well as the schematic.
Here is a parts list and layout as well as the schematic.
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Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Even circa 1989 amps I have gone thru have had bad power supply filters, even if they are not bad yet, while your in the boiler room change them out!
In face change out the first 2 factory 100 uf caps for 220 uf and be sure to check the diodes on each primary leg of the OT.
In face change out the first 2 factory 100 uf caps for 220 uf and be sure to check the diodes on each primary leg of the OT.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Working on getting the PCB out. It sucks. There are these little ribbon wires that connect the separate control PCB to the main PCB. As I try to work the solder-less connector terminals that that tie everything together in this amp loose these ribbons are disintegrating. Looks like I have to remove the front PCB too and replace the ribbons with actual wire. Anyone know if I can replace diodes 101-108 with 1n4007s?
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Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Yes 1n4007 is fine.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
D101 and D102 are flyback diodes on the ends of the OT. If you use 1N4007, you should put three in series.
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Thanks for the replies. I'm going to try to rule out the power transformer today and then order some parts.
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Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Those brown burned spots on the PCB don't bode well for the future. I wonder what the glass transition and decomposition temperature for the those boards is. Anyway, good luck with the repair. It seems the guys here have you on the right track.
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Anyone have any tips for checking the PT? I can unhook all the leads from the board I believe. The fuse only trips with the HT on so I'm assuming I could potentially have a shorted HT winding? The brown spots are definitely not a mark of quality!
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
Correct, according to the parts list D101-102 are 3KV rated.Firestorm wrote:D101 and D102 are flyback diodes on the ends of the OT. If you use 1N4007, you should put three in series.
The idea is to damp any flyback on the OT primary without shorting.
reddog
Re: Fender Super 60 Red Knob Diagnosis (Blowing Fuses)
The power transformer is good. Time to order some parts.