WAS .... PDP-11/23+ and rx-02 drives, need help!!!

Tony Duell ard at p850ug1.demon.co.uk
Sun Jul 10 14:59:59 CDT 2005

> I just went through  10 sets of RK-02s and only got 4 going.  Most 
> have bad boards.  It seems that the lower board is the worst with
> 5 bad.  Most of these came from a Damp location. Someone else had 
> them stored in a barn.  I have tested these by swapping the boards 
> into the working machines and using the boards from the working 
> machines in the test machines.  On the Hardware side, after cleaning

I will refrain from flaming _again_ about that...

> and lubing all seemed to be OK. At least they could boot from either
> drive.
> Anyone had any luck repairing the boards ????

Sure. They're not particulalrly complicated.

The lower board contains several different functions. The read/write 
chain, index and track 0 sensor circuits, the head load solenoid driver, 
the stepper driver, etc. The first job is to determine which function(s) 
has failed. Then you know which bit of circuitry to dive into. Most of 
those sections are simple.

The upper board is more difficult to debug. It's actually a processor 
built using a couple of 2901 ALU slices and 3 2909 (or is it 2911) 
sequencer slices. A listing of the firmware is useful (DEC, AFAIK, never 
supplied this, I had to disassemble and hand-comment it from one of my 
drives), as is a logic anaylser. Then you can check to see (a) what 
routine is being executed and (b) if the sequence of instructions is at 
all sane. 

> What effect does the moisture have on the boards ???? They where not
> outside just damp air.
> I have cleaned them with board cleaner and checked the switches for
> operation. Some of the IC pins are getting rusty. Are the IC's sealed
> very well or can moisture get in the chips

In theory they're hermetically sealed, in practice it is possible for 
contaminants to get into plastic packages (particularly). 


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