"Mark D. Zacharias" wrote in message
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"Arfa Daily" wrote in message
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"EADGBE" wrote in message
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Arfa:

You hit the nail on the head. The problem appears to be related to
the power supply...or at least to a component downstream from the
power supply.

Right next to the connector that leads to the laser assembly, one of
the contacts is labeled "5V". Measuring this contact gives me less
than half a volt under all circumstances.

This 5V contact leads directly to the collector of a 2SA1270
transistor. The transistor checks out OK, although the same half a
volt reading is measured at the collector. There is a jumper wire
that leads to the emitter of this same transistor. It is also clearly
labeled "5V", and it measures a healthy 5.08V.

The base of this transistor is connected, via a 10k resistor, to the
middle lead of a very small transistor with "C114" on the case. If it
is a 2SC114, I cannot readily find a replacement for this transistor,
and I cannot find a datasheet, either, so I don't know how to check
this transistor. It gives me weird readings whenever I test it in
standard NPN or PNP pin configurations. IT DOES NOT SEEM TO BE
DEFECTIVE, HOWEVER, because there are several "C114" transistors and
they all give me extremely similar readings whenever I attempt to
measure them in standard NPN and PNP pin configurations. There are
also a couple of 100uF/16V electrolytics in this circuit used as
couplings to ground, but they check out fine with my ESR meter and my
analog ohmmeter.

I am going to attempt to keep checking upstream to see where things
break down.

Hmmm. I haven't specifically looked up this transistor, but I think you
would be correct in assuming that it is "2SC", in which case, it is NPN
by default. However, that said, if the readings are 'odd', and compare
similarly with others of the same number, then it's probably one of the
types which has internal resistors connected to some of the terminals -
these are very common. From the configuration that you are reporting, I
would suspect that this is in fact a switch circuit, probably driven by
the system control micro, so it may or may not be faulty. At an
'experienced guess' I would think that you would be expecting to see some
change in voltage level at the 10 k resistor, and further back at the
base leg of the small transistor, as a result of shifting the unit from
some quiescent state to an active one i.e. from "standby" to "on" or from
"stop" to "play". If you do see such a level shift, but the 5v never
appears at the output of the 2SA1270 (which will be PNP, incidentally)
then you do have a problem in this circuit. If you're brave, you can
always link the collector of the 2SA to its emitter, thus 'simulating'
the switched on condition, and see what happens. It will at least tell
you if the primary problem is anything to do with this voltage apparently
being missing. If you're not quite brave enough to do it by putting a
screwdriver tip across the transistor leads, solder a 1 ohm fusible
resistor across there.

Arfa


The "114" is indeed a digital transistor, a DTC114.

Mark Z.


Thanks Mark. There you go then. Mark confirms that it is a DTC114 digital
transistor, which means that it is a conventional bipolar type, but with
internal resistors. This all but confirms what I was thinking, and that it
is a switch stage for a 5v rail to somewhere, derived from a permanent 5v
rail, that you are looking at.

Arfa