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MX 3000a early clip?

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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2022 at 12:39pm
Closest I have any experience of and is possible to get would be:https://www.mouser.com/datasheet/2/408/toshiba_2SC4793-587292.pdf

But I see that the original stands a collector current of 1.5A vs 1A and a base current of 150mA vs 100mA of the 2sc4793.

Hmmm, perhaps not then...Confused




Edited by Randy Bohannon - 30 November 2022 at 1:28pm
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Greg32 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg32 Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2022 at 8:01pm
Thanks Randy, they might just work. collector current should be around 240ma.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg32 Quote  Post ReplyReply Direct Link To This Post Posted: 16 December 2022 at 10:53am
Update i have replaced the output devices with mjl1302 and mjl3281 and the pre drivers with  MJE15032/33 the service manual suggests to set the bias at 100-110mv accross the driver transistors emitter resistors, this value only just turns on the output transistors with 1mv across the output transistors emitter resistors, that is about 4.5ma per device which seems a bit low. all other voltages seem to be good. more testing tomorrow...

Edited by Greg32 - 16 December 2022 at 10:54am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg32 Quote  Post ReplyReply Direct Link To This Post Posted: 19 December 2022 at 1:50am
I never tried changing out the step driver boards on the -ve side, the high rail step driver board has 2 leds that are illuminating as signal level is increased, I only saw 1 led on my other mx3000a. what is the correct sequence of led illumination? or what do they indicate?
Thanks Greg
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg32 Quote  Post ReplyReply Direct Link To This Post Posted: 26 December 2022 at 7:07am
Ok finally got time to try swapping out the negative step driver board, success it works. 
now i need to find a replacement board.   qsc # ic-000090-00
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 26 December 2022 at 4:23pm
Well done on diagnosing it at last Greg!Thumbs Up

Edited by Randy Bohannon - 26 December 2022 at 4:23pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greg32 Quote  Post ReplyReply Direct Link To This Post Posted: 27 December 2022 at 7:14am
Thanks Randy, Me being impatient I had a go at repairing the step driver board, i couldn't get the sot-23 devices(quickly at this time of year) so i used the to-92 version 2n3904 and 2n3906. looks rough but functions as it should. 
  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 27 December 2022 at 2:39pm
Should be fine unless it's going gigging again. :)
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