I have cooked the reset circuit on my JP-6 by shorting the +15v and RESET lines on the power supply. Trouble shooting has revealed TR6 on the CPU board is no longer switching so I plan to replace it. The original part is a 2SC2603-E or 2SC2021-Q, long since discontinued. There are a reasonable number of equivalents out there in the same package and pin-out. Before I go ahead and purchase some, I wanted to ask if anyone has replaced these parts previously and with what part number.
in the schematic TR6 seems to be used as a simple switch.
you must choose a similar NPN transistor (same VCEO = 50V and Ic=0.2A) with at least the same gain (150-300 defined by the “E” group from the datasheet) due to the high base resistors (330K/1M).
by calculating with the schematic diagram a gain over 10 will be enough to work.
the TR7 collector current is 4.4V/100K=44uA
the base current is 4.4V/(330K+10K)=13uA
44uA/13uA = 3.4 with a saturation factor of 3 a gain of 10 would be enough.
For me, any standard VCE0=50V NPN TO-92 tranistor with the right pinout and a gain more than 10 could fit to replace TR6
Hi Franck, thanks for your response. Closest I could find (unless buying ‘Ebay’ parts of dubious origin) with the same pinout was the BC187L from Farnell - part of their Multicomp own brand. Let’s see how it goes!
No problem marpat