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HP 8595E Restore and Tracking Generator Questions

Chad All Messages By This Member #122412 Just want to start out by saying I have no background in EE but I am a ham who has restored an older tube radio (SB-101) as well as two Tektronix 24XX scopes (recapping both was the ultimate fix for the scopes).? Somewhere along the way of fixing the Tek scopes I got bit by the test equipment bug and thus began my search for an older SA that I could work on.? I seem to really have developed a liking to this vintage 80’s test gear; the main reason is that they all seem to be well documented, still have a following, and I can actually sorta work on them.? Plus, it’s also nice knowing that I’ve saved a bit of history when getting some of this older test gear and getting it back to working. ? I was lucky enough to come across an 8595E (which is wwaayy more than I need for ham radio use) but couldn’t pass up on the price.? It was sold as parts and when I got it home to the house I was really surprised when I fired it up and it came to life.? First thing I did was copy down the calibration constants for timebase, flatness, and attenuation as I do not have the equipment to calibrate this guy (at least not yet - ?).? Ran through the cal freq and cal amp and it completed successfully so I ran the cal YTF and it successfully completed.? From what I read 300MHz at -20 dBm should mean that it’s calibrated where it needs to be and that’s what I was seeing? so I hooked it up to my cheapo sig gen and played around a bit and it all looked good to me.? Overall I am really happy that I ended up with this piece of test gear.? ? Now for the first issue – the next day when I went to power it on nothing would happen.? I fiddled with the power button and found that if I pressed it and kept it pressed I could get it to come on but once I released the button it would turn off.? Pressed it a few more times and got it to come on without me holding it.? So did some searching and reading and I guess I am looking at possibly a power switch or some bad caps in the PSU.? Since the only power button I can find is attached to a front face plate, and they want more for that then I paid for the SA, I’m going to start with a recap of the PSU.? Couple of question on that subject – ? 1. Are there any recommended caps types for this scope?? With the Tek scopes I was basically told use the best you can find (not an easy task this day and age) and as long as they are not the cheap Chinese caps you should be fine, as even general purpose caps you can get today are spec’ed way better than what come in it from the 80’s.? Just want to confirm that’s the case here as well. ? 2. Are there any recommended parts to replace while I am in there working on the PSU?? On the Tek scopes there were some recommended resistors to replace while doing the recap.? I have not ran across anything specific in the searches I have done for the HP859X. ? 3. I figure I will replace the battery and supercap while I am in there.? I was just going to pull the battery out and re-enter the constants.? Did I capture everything I need with the timebase, flatness, and attenuation numbers or are there some others I should get while I still can??? ? 4. Any thing to watch out for or be mindful of?? Things that break when taking apart or putting back together? ? Now that those questions are out of the way I wanted to ask about the practicality of getting the parts and adding a tracking generator to this guy as it did not come with one?? I’ve done a little reading and watched a video of one being added.? From what I could tell the SA will recognize it without any type of firmware update and the main parts are – ? 1. The tracking gen itself (5086-7917) 2. Step Attenuator (0955-0679) 3. Control board (5063-0635) 4. LODA (5086-7744) ? As most of the parts can be found the main problem I see, aside from the price, is that they normally do not come with the hard lines or cables to connect them.? So, I am going to preface this by saying I am using this for ham radio use, and as of right now I highly doubt I will ever be using this to test device in the GHZ range, so, can SMA soft line cables be fabricated and work OK or is there too much stray RF in the device for that to work?? If so what is recommended cable type? ? So the other option that I have seen regarding added TG functionality, and it’s definitely the cheaper option, is to fabricate a LO out and then use an external generator and passive mixer – which is what I did for my TinySA (definitely wasn’t a perfect solution but it works).? Are any additional HP parts need to get the tap for the LO out are is it as simple as tee’ing it off and running the line to an external port?? If so where is it recommended to tee into? ? I know I’ll have more question and just want to say ‘Thank you’ in advance to anyone who responds. - Chad K5EQ
freshndaire All Messages By This Member #122440 ?Chad-? Check the switch with a meter when it won't power up to see if the contacts are okay.? I'd do that before going after the caps since it was working for a while. ? The contact lube in the some of the old HP switches gets hard and can cause intermittent contact if it gets in the way.? You could just spray the switch with a spray contact cleaner but it can make a bit of a mess and may not get to the right areas inside the switch.? It is also hard t get to it.? The easiest thing to try after confirming it is the switch is to unplug the unit and cycle it a bunch of times then check the contacts again or just plug it in and give it another try.? A little heat from a blow dryer (not a heat gun- too hot!) will often soften the hardened lube enough to get it to move out of the way, sometimes for a very long time. ? I worked at HP for 23 years and have had this problem on several instruments at work and on the ones I bought at the scrap auctions for home.? The old voltmeters were the worst, but easy to disassemble those switches. ? Your unit may be different but here is what I just did.? I have an 8590A with a dead display, the switch in that might not be one that can be safely disassembled, I have not been into one like it.? There is an easily accessible connector in the 8590A (after pulling the cover) in the right-rear corner just forward of the power connector.? I have been meaning to see what it would take to get the (dead) display out, so this was good motivation to finally take a look at it.? I removed the cover and took the left side frame off and loosened the front screws on the right side frame.? Then I pulled the 2 screws out of the bottom of the front panel and I could swing the front panel out enough to get to the power switch.? One screw holds it in.? I also pulled the display out (4 screws on the bottom) after disconnecting the 2 cables to it.? Pretty easy actually, I should have done this long ago.? Now to decide if I want to work on it soon or put it all back for safe keeping.?? It has a note on it: "Display bad" and "Replacements are no longer available per the service center 01-15-2004".? I haven't had it since then but an embarrassingly long time anyway. Clay Scott?
Chad All Messages By This Member #122462 Well I pulled the cover off and unsoldered on lead from the switch.? Sure enough it was open.? I hit it with some deoxit from the top where there was a grove going in and worked it a bit and it seems to be good now.? Once I got the switch out I was able to find some numbers on it and searched for 'sds 3p switch' and was able to find a used match in China -?SDS 3P-5A-80A~ 250V~ 4 foot bracket length 26mm Hole distance 20mm.??Hopefully that will help someone else out.? I searched Mouser but sometimes it's overwhelming searching that site and I wasn't able to find anything that matched.? Looks like I'm good for now on that part.
Dave Wright All Messages By This Member #122478 Chad, For the money you will spend on getting together the components to add a tracking generator to your SA, you might want to consider any of the tiny VNA variations available. I have the 9593E with the TG, and have had it apart several times to troubleshoot the TG. Pretty much a plumbers nightmare, as you have seen. A VNA will give you more information than the SA / TG can. Now, if you are after a learning experience, digging into the guts of your 8595 will give you that.! As for things to look out for, if your model has an input bandswitching relay, there is a modification you can make to reduce the drive current to the relay coils. In the 8593E the original circuit has the habit of cooking the coils, leaving you stuck in either low band or high. Symptom is not hearing the relay click when changing bands.
Jim Ford All Messages By This Member #122482 开云体育 Ah, the too much current for the relay coils issue.? About 20 years ago I had to design a circuit to put out a pulse of current to kick-start a relay.? The hold current necessary to keep the relay closed was about 1/3 the kick-start current, so about 1/9 the power dissipation.? So I dropped the current by a third after a number of milliseconds after switching.? There may be a similar issue here.? HTH.? ?Jim Ford? Sent from my T-Mobile 4G LTE Device toggle quoted message Show quoted text -------- Original message -------- From: Dave Wright <davewrightsplace@...> Date: 2/14/22 6:52 AM (GMT-08:00) To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP 8595E Restore and Tracking Generator Questions Chad, For the money you will spend on getting together the components to add a tracking generator to your SA, you might want to consider any of the tiny VNA variations available. I have the 9593E with the TG, and have had it apart several times to troubleshoot the TG. Pretty much a plumbers nightmare, as you have seen. A VNA will give you more information than the SA / TG can. Now, if you are after a learning experience, digging into the guts of your 8595 will give you that.! As for things to look out for, if your model has an input bandswitching relay, there is a modification you can make to reduce the drive current to the relay coils. In the 8593E the original circuit has the habit of cooking the coils, leaving you stuck in either low band or high. Symptom is not hearing the relay click when changing bands.
Dave Wright All Messages By This Member #122493 Jim, HP uses a mechanically latched relay in the 8593E and others. But, the drive circuit is not an impulse type. The current is continuous, and leads to excess dissipation in the coils. Details here:?/g/HP-Agilent-Keysight-equipment/topic/31717125#96700 _Dave KC6UPS
Jim Ford All Messages By This Member #122494 开云体育 I figured as much. In that case, one would need to set the current high enough to reliably kick-start the relay coil but low enough not to burn up the coil.? Assuming that's possible. May not always be.....? ? ? ? ? ?Jim Sent from my T-Mobile 4G LTE Device toggle quoted message Show quoted text -------- Original message -------- From: Dave Wright <davewrightsplace@...> Date: 2/15/22 8:36 AM (GMT-08:00) To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP 8595E Restore and Tracking Generator Questions Jim, HP uses a mechanically latched relay in the 8593E and others. But, the drive circuit is not an impulse type. The current is continuous, and leads to excess dissipation in the coils. Details here:?/g/HP-Agilent-Keysight-equipment/topic/31717125#96700 _Dave KC6UPS
Jim Ford All Messages By This Member #122495 开云体育 Oh, and if you are driving an inductive load like a relay coil, motor, or I suppose an incandescent bulb or a speaker, don't forget the flyback diode to protect the driving transistor.? A fast recovery diode, reverse biased in normal operation, will shunt the inductive flyback kick around the transistor.? ? Jim Sent from my T-Mobile 4G LTE Device toggle quoted message Show quoted text -------- Original message -------- From: Dave Wright <davewrightsplace@...> Date: 2/15/22 8:36 AM (GMT-08:00) To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP 8595E Restore and Tracking Generator Questions Jim, HP uses a mechanically latched relay in the 8593E and others. But, the drive circuit is not an impulse type. The current is continuous, and leads to excess dissipation in the coils. Details here:?/g/HP-Agilent-Keysight-equipment/topic/31717125#96700 _Dave KC6UPS
Chad All Messages By This Member #122519 开云体育 Dave, The mod looks pretty straight forward. I’ll get it done this weekend. ? We’re you ever able to repair any of those relays? - Chad toggle quoted message Show quoted text On Feb 15, 2022, at 10:35 AM, Dave Wright <davewrightsplace@...> wrote: ?Jim, HP uses a mechanically latched relay in the 8593E and others. But, the drive circuit is not an impulse type. The current is continuous, and leads to excess dissipation in the coils. Details here:?/g/HP-Agilent-Keysight-equipment/topic/31717125#96700 _Dave KC6UPS
Dave Wright All Messages By This Member #122654 Chad, Have not tried to repair the fried relay, as I was able to buy a lot of 3 (lucky) some years back. Also, your particular model may already have the series resistor or other mod added later. You will have to look at the board ( ummm... A10..?) to see what is actually there. And, you might as well invest in the CLIP from Artek if you want to do component level work. I have discovered that the .pdf scans you get from Agilent on the old gear are pretty bad, and no text search capability... _Dave KC6UPS

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