Desperately need BA11-N/BA11-S Technical Manual

tony duell ard at
Wed Sep 16 14:19:06 CDT 2015

> Yeah, as per my 'where are subsystem prints' page, they are in the 11/23
> print set MP00740, pg. 81-87 (schematic on pg. 87):

OK, got it... A one page schematic, a board witht 4 ICs. Shouldn't be too hard...
(famous last words!)

OK, first thing, the things that look like op-amps are in fact comparators. They
have open collector outputs. I would read the LM339 datasheet if you've not 
come across this chip before. It is a very common IC.

Because of the power connections to E1 and E4 (shown on the right hand side of
the schematic) the ouptus swtich between -12V and floating. This means that 
resistors connected from said outputs to ground are actually pull-up 
resistors. That threw me for a few seconds!

The 555s are being used unconventionally. But let's not panic for the moment.

Since you have a working board, the first thing I would compare is the reference 
voltage from D2. Measure the voltage on pins 7 and 9 of the chip E1. 

If that's the same on both boards, attempt to isolate the problem by checking 
the voltage on in 3 of the 555 timers. Are those the same on the good and 
faulty boards?


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