This is the first KA-907 I have worked on. While stripping this down I found a few road blocks.
First, the large supply capacitors are soldered to the power supply board, which is soldered to
the copper chassis. The solder joint is massive.
Second, the power supply leads to the main power supply board have very little "extra" length.
The solder joint runs the full
length of the copper ground
strap. You can't tell from the
picture, but under the copper
strap is a solid bead of solder,
which runs from end to end. I
did not want to attempt to
remove that much solder. The
copper frame will act as a big
heat sink, which will increase
greatly the amount of heat
needed to loosen the solder.
There is a big risk of damaging
the board doing this.
There was not enough free wire on the transformer leads to allow for rewapping the
wires. Each time a wire is unwarpped from a post, you lose the length of wire which
was wrapped around the post. This is generally about 1.5 - 2 inches. You will need at
least this much "free" wire to strip and rewrap. Kenwood usually leave generous
amounts of wire in their units for this. hummmm... someone been in this unit before? or
is this a cost cutting thing?
I decided that a complete strip-down was too risky. The risk of causing unrepairable
damage was too high. I decided to restore the amp in sections. This included new
caps, washing all surfaces, grooming the components on the boards, and then voltage
checks after assembly.
1. First the center section of the amp (power supply boards, transformers, and center
section of the chassis.
2. Frontend (tone controls and front chassis section)
3. Backend (inputs, back panel, back side of chassis)
4. Output sections (output tansistors, heat sinks)
5. Face plate, cover, bottom plate, knobs