HP-8116A Away Around This? - Page 1
Forum section: electronics / repair

author: Mick B
author_rank: Regular Contributor
timestamp: August 02, 2021, 04:19:55 pm
content: I started to Cal this HP-8116A-(001) unit. All going well until it called for using a 20db Attenuator and changing the Attenuation factor on my scope, I have attenuators. WHAT I DON'T HAVE! Is a 20x factor setting on my scope 1x,10x,100x,1000x. Is there anyway to get around this short of a new scope this one is not old?Thanks Mick

author: Andy Watson
author_rank: Super Contributor
timestamp: August 02, 2021, 04:54:42 pm
content: The HP 8116 has a voltage output, therefore, 20db = 10x.

author: MarkL
author_rank: Unknown
timestamp: August 02, 2021, 05:09:35 pm
content: What section of the calibration procedure are you referring to? What scope do you have?The procedure is written for a 54121T 20GHz scope, which is major overkill for what's needed to do a decent calibration on the 8116A. They have selected attenuators to stay within the vertical range of that scope, which is only 1mv/div to 80mV/div.While not knowing the specific section, it should not be a problem to use x10 attenuation instead with the appropriate vertical setting on your scope which results in the same (or close to) the number of vertical divisions for the signal you want to examine. Note that you will need to use 50ohm input impedance on your scope if you want to follow their procedure with attenuators (the 54121T is 50ohms). Or you can just figure out what they're trying to accomplish in each step, and set that up specifically for your equipment.Personally, I would not mess with the factory calibration unless you know it's off. Some of the adjustments are very sensitive to the slightest turn, and many interact with each other. It will drive you crazy trying to get it perfect (speaking from experience).

author: Mick B
author_rank: Regular Contributor
timestamp: August 03, 2021, 02:12:09 am
content: Hello MarkL, good to hear from you again. I saw this video and I think I can do thishttps://youtu.be/LJ-PsPow10MIt doesn't look like all the adjustments but enough to bring some of the voltages and and frequency's a little closer.The manual im using is an Operating, Programing and Servicing Manual for serial number 3134G11521 its 397 pagesand 50,648 KB large I can e-mail you or dropbox you a copy if needed, so were both on the same page.I left off on (adobe page 147) but it's 9-4 Titled "Square Low Amplitude & Offset"I have 20db and 6db attenuator's and 50Ω terminator's and a large assortment of 10 turn pots. the scope I have is a Hantek DSO5072P with mod also have a HP-8590A Spectrum Analyzer and HP5334A Counter AND also another HP8116A WITHOUT option (001). I'm just learning this stuff what an education. Wish I would have started this at 20 instead of 65 But i'm having a blast none the less. Thanks again for your help MarkL

author: bdunham7
author_rank: Super Contributor
timestamp: August 03, 2021, 04:07:14 am
content: I don't recall the details but I did a repair (hybrid IC, power supply) and calibration of one of those last year and there wasn't anything that couldn't be done with a bog standard scope if you just waded through their descriptions and figured out what they actually want. There's a lot of twisty pots and it's pretty tricky to get the sine wave all dialed in nicely with minimal distortion. On mine pretty much everything was out of whack and I would limit your expectations to somewhere between pretty good and good enough.

author: jonpaul
author_rank: Super Contributor
timestamp: August 03, 2021, 12:41:37 pm
content: Mick B BRAVO for your project.Exactly why do you think it needs CAL? After major repair? Water damage?1/attenuators are needed to reduce reflections and aberrations, 20 dB is a factor of 10X in V. No effect on the scope V ranges at all.We use Mini-Circuits HAT-x series inline BNC attens very fine , BW DC- 1 GHz and avail in all dB atten.https://www.minicircuits.com/WebStore/dashboard.html?model=HAT-20%2BAny scope with sufficient BW and sensitivity is fine. Avoid Chinese knockoffs, we use Tektronix 2465B.2/ Easy to locate the proper manual for your SN.https://www.keysight.com/us/en/assets/9018-05117/user-manuals/9018-05117.pdfhttp://userequip.com/files/specs/1562/HP%208116A%20Operating%20&%20Service.pdfEpay or Artech has printed versions.3/ Suggest to reRead the 8116A spec and do a quick performance check, as the CAL is not trivial and can make things worse.Beware that the freq indication is NOT a counter and can have errors of a few %.I had several 8116A, and NEVER had to do a CAL.Most have sticking rocker switches.4/ I recall a battery to store the last setup but the CAL is all analog pots and caps and NOT dependent on the battery.Except for the loud fan and rocker switches, its a great unit, very versatile.An HP classic!Enjoy and Bon Chance,Jon

author: Mick B
author_rank: Regular Contributor
timestamp: August 03, 2021, 10:58:54 pm
content: Hello Jonpaul.I have 2 of these and the outputs are very different, hence the need to cal one of them if not both. I want the peace of mind thats its in the ballpark I am aware these are not precision instruments but like I keep hearing close enough. I need to be right in my mind that when it says close enough I know what that means. Make sense?1. Thanks for the link to Mini-Circuits.2. One of the several Manuals I have for this unit is for serial number 3134G11521 the serial number on myunit is 3134G1673. So I think i'm good there.3. I have read the manual almost cover to cover and lots of places 10's of times. Seems the performance check is just about as long and involved as the calibration. After starting the performance check it became obvious somethings were off and others on the edge so I stopped checking and started the CAL process. and here we are.NOTE: The first problem to come up was the Voltage Rails! I could not resolve -5.2, 5.0, and 5.1 so i went through the schematic the 15v rail was ok so I started looking at VR1, R11,13,14,15. for a drifting component. What I found was R15 was bodged and 2 resisters in its place??? It had a brass grommet on top looked factory. WTF? and then I found this.(See attached file) And now the 5volt rail voltages are resolved WOW! what a way to start off.Thank you for your interest in this project.