After taking the Main PCB Assembly out of the Roland TR-808,
you'll notice a flat, flexible ribbon cable running from the step
switch board to the Main board (right).
This Flat Flexible
Cable, or FFC, unplugs from the Switch board, letting
you move the Switch board freely while working on it.
These flexible circuits sometimes crack, as seen here, and need to be repaired
or circumvented.
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Here you see a TR-808 whose broken FFC had been discarded and replaced
with a ribbon of twelve wires.
At one end of the ribbon, the wires were soldered to the circuit traces
underneath the FFC
connector on the Switch board
(right).
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At the other end, the wires were soldered to the pins on the Main board
(right) that
previously soldered to
the flexible cable.
The disadvantage of this fix is that the Switch board and the Main board
are always wired together.
During repair and maintenance, whenever you turn over the Switch board, the
wires bend, quickly breaking them at the solder points.
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Here you see another TR-808. Its ribbon cable was in good shape except for one fatal crack
that kept many of the step switches from working.
As shown here, we used a small X-ACTO knife to scrape away the resist from several of the
copper circuit traces.
Both sides of the crack looked sturdy so we
decided to repair the FFC with some solder and some small wire jumpers.
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We taped it down to a flat surface and scraped some resist from both sides
of the crack on all 12 of the circuit
traces.
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We then melted a drop of solder onto each copper pad.
Then we cut short pieces of flexible, stranded wire
and pre-tinned their ends with solder.
Finally, we re-melted each solder drop and quickly merged a pre-tinned
wire end into the drop.
We didn't want to give the molten solder enough time to seep into the center of the
jumper, making it inflexible.
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Here you see the finished repair of the Roland TR-808 ribbon cable.
The advantage of this fix is that the switch board still disconnects
from the main board, making the
switch board much easier to work on.
In addition, everything except the mended cable remains original.
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We insulated the exposed wire jumpers with plastic electrical tape so they
wouldn't short out to the front lip of the TR-808 chassis.
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