[time-nuts] 5370A vs 5370B

[Ed Palmer]

One trick I always use to quiet down a rowdy fan is to replace the 
mounting screws with rubber mounts.  This isolates the fan's mechanical 
vibrations from the chassis.  The difference is audible - even with a 
good fan.  I salvaged some mounts  from IBM machines that work great.  
Most of the big online computer retailers have something along these lines.

Ed

Mark Sims wrote:
> Yes,  I replace the standard HP fan with a MUCH quieter one.   I get mine from a local surplus shop.  It is made by AAVID.  it draws 120 mA at 12V and I  run it off the 10V supply (which is somewhat over 10V).   
>
> I don't have one handy to get the part number.  They also have a 160 mA model part number 148A233.  (Hint,  fan noise correlates greatly with power drawn).   There is also a Panasonic model that is particularly quiet (but the store owner keeps them for himself).  Just about any fan that fits will work.   It is VERY difficult to get one of the fan screws back in without stripping the machine... I leave it out.
>
> Before getting all whiny about overheating,  careful HP engineers putting that obnoxious hurricane in for a reason,  etc...  know that I put several thermocouples all over the guts of the machine and found no significant changes in cooling.   I have had modified machines running continuously for many years.
>
> I usually use an external reference,  but like being able to use the internal one.   Hence the tweaker hole above the OSC (also do that on the 5371 and 5372).   It is a royal pain to set that slug anywhere near close enough.  Basically you tweak it randomly enough until one gets close enough (I try to get the freq display to under 10.000 000 005 0)
>
> Another dumb aspect of the 5370 design is that the CPU is clocked by the 10 MHz oscillator.  Switch the timebase while it is running and the thing crashes...
>
> Those slide switches on the front panel are actually a nice design... except they are located where the fan deposits all that rust,  dust,  bits of fluff,  cat hair,  cheerios,  smutz.   You would not beleive the hairballs that I have pulled out of that area.   The switches are sliding contacts over a gold plated PCB.  The support frame of the switch leaves the contacts  open to the air.   Easy enough to clean,  but a royal PITA.
>
> Also note that when modifying the reference buffer board that the LED does not turn off after you do the mod,  it just gets a little dimmer. 		 	   		  
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