[Tim Schwartz]

EADGBE wrote:
OK, I have pulled apart my BX-300 to try to diagnose the problem it
has.

To refresh everyone's memory, this cassette deck is the one that keeps
returning to PLAY mode, even after you press STOP and remove the
tape. Also, the digital tape counter keeps flickering and re-setting
itself to "0000" even while the tape is playing/rewinding/fast-
forwarding.

Someone told me to check for voltages on the two PC boards involved.
One PC board houses the counter and the other PC board houses the
function buttons (Stop, Play, RW, etc.).

According to the service manual, both of these boards should have a 5
volt DC power supply going to them at all times.

I turned the unit on and measured the voltage coming into both boards.

Exactly 5 volts was present on both boards, with NO fluctuation at
all. Solid as a rock. (5.01 volts, to be precise.)

Even when the counter kept flickering and re-setting itself to "0000"
and the deck kept returning to PLAY, the DC voltages on both boards
was a ROCK STEADY 5.01 volts.

What's my next move? Any and all assistance will be GREATLY
appreciated.

Hello,

First, I'd check that the electrical switch for the play mode isn't
defective, put an ohm meter across the switch and it should show near
open when you are not pressing it,and a short when you are. Also check
the time record switch is really off. The next thing I'd look at are
the three fingers of the leaf switches on the cam gear on the back of
the mech, as I've seen these switches cause all sorts of weirdness if
they are not making good contact. They are a pain to clean, and be
careful not to bend them.

As to the counter, as I recall this is an optical driven one from shiny
parts of the take up reel. If the machine is really dusty, the optical
sensor might be going nuts. I've found the electronics in these
machines to be quite trouble free, so I tend to think of contact and
mechanical issues. However, it couldn't hurt to put an oscilloscope on
the power supply lines to make sure they are clean. I'd also look for
overheated solder connections in the power supply.


Regards,
Tim Schwartz
Bristol Electronics