Re: [WANTED] HP 85700A 32kB RAM card
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Hi,
In this thread on eevblog forum: It is listed undocumented gpib commands for the 856xE series, one can be used to read any memory location. I have no idea if this works with the 859xE series. These commands is not accepted by my 8562A.
But as Greg writes, I would do the pen and pencil backup for the important data first.
Br, Askild
On Sun, Mar 1, 2020 at 2:10 AM Greg Muir via Groups.Io <big_sky_explorer= [email protected]> wrote:
Ron,
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The 85700A isn¡¯t going to help you much if you plan to replace the NVRAM battery B1 on the video/processor board.? The calibration constants have to be manually logged per the instructions in section 3 of the ¡°HP 8590 Series Assembly-Level Repair Service Guide¡± titled ¡°Backing Up And Reloading Correction Constants.¡±
()?? The method to retain the correction constants falls back on good ol¡¯ paper and pencil using the forms included in that section.
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As for battery replacement without losing the constants, I use a procedure utilizing a bench supply.? I first remove the memory subassembly from the analyzer since it contains both the memory and backup battery.? Then I tack a ~1k ohm resistor to the positive side of the battery trace and a wire to the negative side (both away from the solder pads that attach the battery) then connect the resistor and lead to the power supply set to near the battery voltage.? This will allow you to retain the battery voltage while you replace the battery.? Use extreme care so as not to short out the supply lines to the memory lest you lose the contents.
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It is also a good idea to add a diode in series with the resistor to prevent any backflow of current should you be using a power supply with a capacitive filtered output and forgot to turn the supply on before connecting it to the + and ¨C sides of the memory board.? A discharged capacitor in the power supply could cause a brief drop in the RAM supply line depending upon where you connect your leads to the board.\
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In all, using care you can easily replace the battery.? I do not recommend trying to replace the battery with the RAM board under power in the spectrum analyzer.? First, it is quite difficult and second, if you use any type of soldering iron grounded to the third wire outlet ground, you can short out the analyzer power supply voltage and not only lose your correction constants but also could do additional damage elsewhere.
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Greg
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