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I have just bought an 8591A that has an intermittent REF UNLOCK error message when I use the internal 10 MHz reference. The error comes every 0,5 to 10 second. The internal reference is 10,000 MHz and the amplitude is around 350 mV peak to peak. The waveform is a bit distorted - not a clean sinus wave. The error REF UNLOCK disappears if I connect an external 10 MHz reference - If the amplitude is exactly 130 mV peak to peak. If the amplitude is higher than 140 mV peak to peak, the intermittent error REF UNLOCK comes back. Also if the external reference is adjusted lower than 9,98 MHz or higher than 10,02 MHz the error REF UNLOCK disappears even if the amplitude is higher than 140 mV peak to peak. My 8591A has serial number 3122U01724 and software revision 7.5.91. I have checked the Service Manual but it does unfortunately not contain any drawings of the A25 Counter Lock Assembly. I am very grateful if anybody has any suggestions!

Ok I replaced the battery this am and all went great, yes I did copy the info as the manual states. my new issue is the display as you will see in this video. I thought maybe I missed a connection when I re-assembled so I took all apart and checked and nothing was disconnected or wrong. https://youtu.be/QGJ8quU_MiM?si=6P0sZImvJVhGCgMF The Voltages look good according to the Power Supply indicator lights. D1 - D16 all lite when powered on and go off with the exception on D13 as I believe this is normal? Any suggestions would be appreciated.

I have Agilent CXA Signal Analyzer N9000A, I'm getting these errors, please help. I referred manual and it suggested to check 50Mhz with -24dB, But when I check in my equipment its showing 50Mhz with -60dB. While I trace it out it was across H270(HMC270MS8G) where I was getting 50Mhz with -60dB but near FPGA it is exact 50Mhz with -24dB, so does it represent there is problem with H270 or any other if yes please help me, And any blue print of this will help a-lot.

Sold the VNA, however, have the local ops manual, very handy with full view foldout. Also, Digital Radio Measurements text. PM me direct, make offer, shipped media mail. Thanks, Alan

I did it ! I replaced the memory battery in my 3457A. My used 3457A was built in the late '80s and still had its original lithium battery, with a 1989 date code on it. This battery obviously needed replacement. Unfortunately, the battery is soldered to the processor PC board and provides permanent Vcc for a low-power CMOS SRAM chip which holds the multimeter's calibration constants. In other words, interrupting the SRAM supply would result in the loss of calibration data. Thus, the battery must be replaced while the 3457A is powered up. This is a bit of a nail-biting experience, but it can be done. One useful trick I used is to prepare a cardboard shield which covers the CPU board and protects it from any solder drops and shorts, while allowing access to the battery. And of course the soldering iron must be floating. Replacement batteries in the original size (lithium BR 2/3AA with solder pins) are still available for a few dollars, but I chose to install a slightly different battery, a Tadiran SL750 which has a 1/2 AA size, for which sockets are available. Using a socket means that in 10 years, the next battery replacement will be easier : with the multimeter powered up, just pop out the old battery and insert a new one. Another advantage is that 1/2 AA lithium batteries are very easy to find, there's a good chance that your local supermarket has them. Now I'd like to share some thoughts and questions about this battery. As we all know, lithium batteries have a long, but finite life. Even though the current drain on the battery is less than 0.2 uA at room temperature, at some point in time the battery will die. I read the 3457A user and service manuals, but I couldn't find a single mention of the battery. Nothing about battery life, no instructions on how to replace it, even nothing that says "contact your nearest HP sales office". To me, this doesn't make sense, especially when considering that this multimeter was introduced in 1986, at the time of the "old HP" which produced high-quality instruments, not expendable stuff. I could only think of a few possibilities : - Maybe the engineers at that time believed that lithium batteries could last forever ; - Or they thought the multimeter would be scrapped when the battery runs out, or before it does ; - Or they decided that if a multimeter loses its calibration data because of a dead battery, it should be returned to HP for battery or processor board replacement followed by re-calibration. That's an expensive proposition. None of these options make any sense to me in the context of the "old HP". Further thoughts and comments will be most welcome ! Joel

Hi, I need some help for my HP 3325A, which worked many years perfect, but know has the common FAIL 2 & 3 Error. (PASS 1, FAIL 2 FAIL 3) It has still sin, square and triangle output, the amplitude is ok, the range is ok (1-10Vpp) into a 50 Ohm load. When swtichting from sin to square or triangle the a-cal error message comes up. The voltages are good, 5.05, -15.16, +15.16 volts, no ripple, or minor. I changes some caps in the psu some time ago. The integrator output looks good, the voltages are as expected on the testpoints LVL,OS1,OS2,AMPL,XDR. I interchanged already U20 & U24. I have a revision C board, the realays on the att board are the flat black ones. Alls tests were done grounding the ACD pin, 1khz and 10Vpp. I found something strange in the amp section. placing the jumper to detach the amp from AMP IN and measuring the DC bias voltage at F3 left and right it shows -12.73 volts. Should be +7.5 volts. When toggeling the jumper and playing with the amp settings, the voltage sudden comes to a normal value and I could adjust the bias with the pot to 7.5 volts. Should it be in any case 7.5 volts after power on and when AMP in pin is disconnected and with any amp setting? I checked already soldering and diodes, resistors, fuses and caps for shorts. And some transitors in the amp section. I have the service manual, there is a huge section testing with a signature analyzer, but I don't have one. So are there any hints, what to test / check next? Am I right in the amp section? Ralf