Troubleshooting a Space Echo

chokeyou · July 15, 2006, 03:43:57 AM

So I've got this space echo, and it worked great. I popped a fuse in it yesterday, put in a replacement today and it works ok again...except the repeat rate pot seems to be stuck "wide open". the circuit varies the speed of the motor based on the resistance of the repeat rate pot. I checked the pot with my multimeter, it works as it should...however, the motor is acting like it isnt seeing any resistance at all. I found the service manual and heres a snippit of the motor circuit w/ the repeat rate pot connection... Anybody see any problem areas...things i should check that might be faulty after seeing a surge of electricity (i'm guessing around the fuse...is that what is shown right by R212?)

snippit: http://community.webshots.com/photo/2210595610059824954dWjnoz

chokeyou · July 17, 2006, 04:28:41 AM

I was able to get in there and test out some voltages tonight. Here are my findings:
http://community.webshots.com/photo/2690190960059824954HfpLMv
(the fishy part is the right side of the schematic) tested voltages shown in red. black handwriting is in my repair manual. this is quite frustrating as I've come across a few components omitted from my space echo and different, renamed components in their place. lots of time lost just looking for the part...meh.

I think the Q13 and Q10 are the biggest offenders. the manual here says Q13 is a 2SD234-O which I read on the internet is no longer made. I didnt find any equivalents, can anybody help me with that? what's the likelyhood of more transistors being fried with those tested voltages?

Paul Perry (Frostwave) · July 17, 2006, 06:07:03 AM

My equivs book has 2SD234 as a silicon NPN 3Amax 25W
equivs bd241A, BD234A same pinout, also BD577, BD587 similar pinout, shape a bit different. Think the case is connected to the collector.

chokeyou · July 17, 2006, 07:07:52 PM

say if Q10 fails, would that explain Q13's emitter putting out 15V? sorry, im no master of transistors

chokeyou · July 17, 2006, 08:01:06 PM

nobody? surely somebody around here right now should be able to identify the non-working transistor. I'm actually starting to think its Q9-Q13...are there any I should be able to overlook? maybe Q11

chokeyou · July 17, 2006, 09:46:39 PM

webshots sucks, heres the fullsize

chokeyou · July 25, 2006, 09:06:09 PM

I swapped Q13 and Q10 to no avail

voltages are the same still...can anybody lend a hand?

billings · July 25, 2006, 10:06:05 PM

What about that 15.7V Vbe drop on Q11 there?

chokeyou · July 25, 2006, 10:34:19 PM

arg i cant find the cross ref page i did originally

i orderred a bunch of transistors and i dont know which ones they are!

chokeyou · July 25, 2006, 10:58:22 PM

can anybody help me find a cross ref list for 2SC828 R transistors?

does it include NTE229?

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Troubleshooting a Space Echo