7 Apr
2012
7 Apr
'12
1:16 p.m.
Rob Jarratt wrote:
The TIP125 are Darlington Transistors, you can't test them very good with
your Diode Tester.
Better use a small battery (between4 and 10 Volts) a samll lightbulb from
the collector to the negative pole from the battery, connect the emitter to
the positive pole and a resistor with approx 10-20Kohms from the basis to
the negative pole. The light bulb should light up then, w/o the resistor not.
Regards,
Holm
--
Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe,
Freiberger Stra?e 42, 09600 Obersch?na, USt-Id: DE253710583
www.tsht.de, info at tsht.de, Fax +49 3731 74200, Mobil: 0172 8790 741
Swapping the
motor control board did indeed resolve the problem. So now I
can look at the faulty board and see if one of the power transistors on
there
has failed.
Thanks
Rob
I have been desoldering the power transistors and testing them with a DMM
using the diode tester. There are eight in all, four test OK as two diodes.
However, the other four are marked 8702 TIP125, have a Texas Instruments
logo, and do not test as two diodes. Looking at the datasheet here
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/4128.pdf it
would seem that it is not they are not simple transistors and so perhaps my
measurements are showing them to be working OK. Here is what I measure with
the diode tester:
1st - b-e 1.95V e-b 0.82V b-c OC c-b 0.66V c-e 0.58V e-c OC
2nd - b-e 1.91V e-b 0.83V b-c OC c-b 0.68V c-e 0.58V e-c OC
3rd - b-e 1.90V e-b 0.81V b-c OC c-b 0.67V c-e 0.59V e-c OC
4th - b-e 1.75V e-b 0.75V b-c OC c-b 0.56V c-e 0.58V e-c OC
It looks like the 4th one is slightly different to the other three, but I
have no idea if this is far enough out of tolerance as to cause the motor
not to turn.
Can anyone tell me if those values look OK, or what else to look at on the
motor control board?
Thanks
Rob