HP8714C  - Page 1
Forum section: electronics / repair

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 29, 2016, 09:02:43 pm
content: I have an HP8714C network analyzerIt has a suspected power supply fault I have looked at the service manual and have concluded this LED status:If the green LED is on, the red LED is on steadily, and the fan is o ffCheck the line voltage selector switch, located below the AC power jack. If it is correct,Not sure where this cable is:remove the power supply/display assembly and make sure that the cable from the on/standbyswitch to the power supply assembly is connected.With the power supply/display assembly outside the analyzer, plug it in and switch theanalyzer's line power ON..On further inspection I used a multi-meter and Peak Atlas DCA pro on the fast rectifier component on the buck converter board of the power supply. All pins seem to be shorted.Problem is I am unable to find this component.Can anyone help with this?R_G_B

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 29, 2016, 09:09:01 pm
content: FEP16DT fast rectifier.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 29, 2016, 09:10:47 pm
content: Buck converter circuit.

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2016, 09:14:00 pm
content: It's a 200V version of these:https://www.fairchildsemi.com/datasheets/FE/FEP16DT.pdf

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 29, 2016, 09:14:17 pm
content: Location of faulty rectifier on buck converter PCB

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 29, 2016, 09:16:58 pm
content: Thanks for the rapid response tautech.

author: TheSteve
author_rank: Unknown
timestamp: April 30, 2016, 02:25:45 am
content: Check the caps, you'll probably find they are leaking.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 30, 2016, 08:38:50 pm
content: I manged to find the link to the schematics on here. The shorted diode pack seems to be pulling all the output voltages to ground.hence I am getting no out put voltages .I checked all the caps using the peak atlas ESR meter they seem to be with-in spec.Thanks TheSteve.R_G_B

author: TheSteve
author_rank: Unknown
timestamp: May 01, 2016, 05:24:30 am
content: Quote from: R_G_B_ on April 30, 2016, 08:38:50 pmThey will test fine - but may be already leaking. I repaired the exact power supply with the diode failing the same way because the caps were leaking. The crap they leak conducts all over the place and freaks out the protection circuits. They all tested fine still. The power supply design is very cool, it has tons of protection to it(as long as the supervisory supply works). Anyway, swap out the needed parts and power it up on the bench, you'll know its good right away if all 4 of the green status LED's turn on.Also if you haven't enabled all of the optional features do it once you get it repaired, and maybe even add in a color LCD as it makes the machine look so much nicer.Any questions at all let me know. I have an 8714C and 8712B in my lab at the moment.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: May 02, 2016, 09:20:52 pm
content: Taking out the the FEP16DT fast rectifier diode revealed it as not being shorted but instead the parallel connected diode FES8CT as being shorted .I was not able to order this. So i had to choose the next component down FES8BT.So its a Peak Reverse Repetitive Voltage 150 FES8CT vs 100V FES8BT.we will see?R_G_B

author: TheSteve
author_rank: Unknown
timestamp: May 02, 2016, 09:28:05 pm
content: I used a MUR815G to replace that part.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: May 03, 2016, 10:23:18 am
content: managed to order MUR815GThanks TheSteveR_G_B