[time-nuts] 5370A vs 5370B

Pete Rawson peterawson at earthlink.net
Wed Mar 10 05:44:31 UTC 2010


Bob,

I think you'll find that the test mode you're describing results from
is setup using A as start & B as stop and the period measurement
is for 1 period.

The resulting 99.x reading has rather wide limits since both channel
trigger level uncertainties are included in the measurement. Unless
you have very carefully matched the trigger points, the results from
your unit are reasonable.

Pete Rawson
 
On Mar 9, 2010, at 6:37 PM, Bob Camp wrote:

> Hi
> 
> Ok, the trigger level pots are bent but functional. The one that was stuck works after a bit of readjustment of the knob. 
> 
> All three inputs (ext arm,  and the two channels) blink when I put the 10 MHz into them. The two with the working pots behave as expected as the pot is turned (trigger in the middle, no trigger on both ends). 
> 
> For what ever reason it seems to think that the period of it's 10 MHz standard is 99.5 ns. In frequency mode it thinks the standard is at 9.998xxx MHz. Obviously it's a little confused ....
> 
> Sounds like it's worth working on, unless the 99.5 ns thing indicates some sort of massive failure.
> 
> Bob
> 
> 
> On Mar 9, 2010, at 7:03 PM, Mark Sims wrote:
> 
>> 
>> I've had the "pleasure" of fixing way too many 5370A and 5370B front panels.  It's been a while so these musings may be clouded...   also beware of the two or three different front panel designs.  Also there are "hybrid" 5370A's out there with 5370B front ends.
>> 
>> There are 4 pots on the front panel:  the 470K display update rate,  a 10K or 200 ohm arming level (200 ohm on 5370B and later 5370A's),  and two 5K trigger level.  All are linear taper,  all have switches,  all are small pots with (1/4"? bushings).   Finding pots with proper switches ain't easy.  
>> 
>> I have never had to do the trigger level pots.  They have metal shafts and seldom break.  Their switches are what you would expect (closed when the pot is turned clockwise).  In the far CCW direction the switch is open and selects the 0V trigger level.
>> 
>> The other two pots are an exceedingly crappy hp design.  They have fragile plastic shafts and really poor quality switches.  The switches need to be closed when the switch is counterclockwise. HP's pots have both normally open and normally closed contacts.   Frankly these pots are seldom used and you can use a switchless pot and just hardwire those pads.
>> 
>> The display rate pots is particularly useless.  You can just hardwire it to max.
>> 
>> The biggest bugaboo in buying a 5370 is the state of the HP custom input amplifier chips.  They can be damaged by overloading the input.   Blow one and you are screwed.  Buy a 5370 with a blown input amp and you are screwed.   The 5370A and 5370B used different chips.  The 5345A counter is a source of input amp chips.
>> 
>> It would be VERY nice if some clever person built  drop in replacement "chips" built of modern SMD parts on a DIP header.  Those input amp chips are socketed.  They are little more than a comparator.
>> 
>> Quick check of the 5370A inputs is to set the unit to "SEParate" inputs and connect the back panel 10 MHz ref signal to each of the inputs.  The signal level LED should flash.  A steady LED means that input is toast (or the input PCB slide switches are full of navel lint and need cleaning).    		 	   		  
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> 
> 
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