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HP/Agilent 53181A Teardown


This weekend was busy ... Been sitting on some stuff for a while and this was the ideal day to crack them open.

A dead 53181. Does not power on. Turns out some of the big ceramic power resistors in the supply had 'desoldered' themselves over time. These machines do not have a real power-off switch. the main supply is always running to keep the oven hot. This particular machine had its oven removed before they tossed it. So i switched it back to its internal TCXO ( it has a smaller TCXO on the main board. installing the oven disables that one and switches the signal over. I have an oven in my older frequency counter so i will transplant it ( HP only has one model oven so they are compatible. just a matter of making an adapter cable )

The power supply. a custom module built by delta electronics. The power resistor just above the transformer had desoldered itself.

THe base board. a motorla 68331 32 bit microcontroller does the heavy lifting. the empty footprint abvove is for  a floating point coprocessor but they never used this. THe service manual for these machines deals with the 53181 53182 and one other model. for each variation the FPU is crossed out. i guess they figured they had enough kick to run the floating point through a library 

the little board bottom right is the boostconverter for the frontpanel VFD
the Xilinx3042 gate array contains the counter logic. the empty footprint can hold an identical 3042 used in the 53182 version of this machine.

Parts left of the xilinx are all ECL 10F series gates and comparators. input ranging relays do the rest.

The frontpanel

First boot : Success !


THe 3Ghz options is a simple MMIC based amplifier followed by a fujitsi divide by 64 chip. i got the schematics and board layout. going to make this thing myself :)


--- Quote from: free_electron on February 11, 2013, 12:47:47 am ---THe 3Ghz options is a simple MMIC based amplifier followed by a fujitsi divide by 64 chip. i got the schematics and board layout. going to make this thing myself :)

--- End quote ---

Looks like someone does a clone (not cheap)
But has the HP logo on it?  :-//

I recently devised a modification to my HP 53131A to replace the stupid soft power switch arrangement with a proper hard power switch.  Simple to do and using a couple of low cost parts, the fan and switch mode PSU only run when you turn the thing on - makes the counter more usable as a bench counter IMHO. Hopefully others will find it useful.


Nice Gerry, though I would have taken the rest of the 4 core screened cable from the AT power supply and used it as well, no extra work and it is shielded somewhat. I would have just checked that there are no traces under the switch and drilled a clearance hole for the rod, then taken an old CDROM drive for the steel laser guide rail and used that as a push rod. Cheap and rugged, plus never going to bend.

Would have been better for them to have had a separate power supply for the oven option, but as they probably cost cutted it down to having a soft switch, as they consider the internal oscillator to be only there for basic use, and they would have needed a rear panel power switch on there as well to turn the oven on and off if needed if it had a separate supply. Do not think test equipment is energy star rated, most consume a fair amount of power when idle if they are using ovenised references or are running stable oscillators.

@SeanB, yeah I could have used screened cable from an old AT, thinking about it that would have been a good source for a power switch too but I don't have anything like that laying around.  I did think about drilling through the PCB and that would work, there is a track but it only goes to a test pad so could have been removed.  I decided against that simply because I wanted the mod to be 100% reversible. Also, the wire I used is bendable (with pliers) which is important because it was not possible to get 100% alignment, the ability to shape the wire was key to making this work properly.   There is no sense of give in the result when you depress the button, it feels just like my other gear that had a hard power switch.



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