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Hi

Can anyone suggest what the problem is likely to be with my Tascam
Porta 07 (a multitrack cassette recorder)?

I'm operating the unit with a 12V 500mA power supply (exact equivalent
to the Tascam brand PS-P2 power supply that goes with this unit) with
correct polarity. The cassette transport works OK, but nothing else
does.

The power light doesn't come on, and neither do any of the many LEDs
including the level meters. There is complete silence from all the
outs including the headphone socket. There is nothing working at all,
except the cassette motor and the cassette mechanism.

I'm guessing that because everything is out, it's likely that there is
one faulty component somewhere which is not letting power through to
the electronics. As I have plenty of spares and could replace any of
the discrete electronics components, it seems a shame to have to dump
the unit if it can be fixed. Anyone have any ideas? Thanks


Start by looking for fuses ( which may not be obvious glass and metal
tubes ). Look on the board to see if there are any voltage test points
marked, or a list of the pin functions of any connectors, where you might be
able to check for supply voltages. If any are missing, or if you can't tell,
then look for transistors or monolithic regulators mounted on heatsinks.
Transistor regulators should have one pin at a higher voltage than the other
two, which will be at a (nearly) similar voltage. For positive rails, if the
transistor type starts "C" or "D" , then likely, the middle pin will be at
the highest positive voltage, the left pin will be at some lower voltage,
and the right pin at a slightly lower voltage than the left pin. For
transistors starting "A" or "B", the right pin will be at the highest
voltage, and the centre pin at the lowest. For negative rails, reverse the
"A/B" and "C/D" descriptions. Monolithic regulators start "78" for positive
types, and "79" for negative types. The next two digits specify the output
voltage, so a 7805 is a +5v reg, a 7812 is a +12v reg. A 7905 would be a -5v
reg and a 7915, is a -15v reg. The pinning for the 78 series is, from the
left, tab away from you, IN - GND - OUT. A 79 series is IN - OUT - GND.

If that information doesn't get you on the track, then it is likely that a
set of schematics would be necessary to get to the bottom of the problem, or
possibly having a more experienced servicer's eye cast over it. Good luck
with it.

Arfa