Agilent 66311B missing trace and resistor - Page 1
Forum section: electronics / repair

author: Dar_Gol
author_rank: Newbie
timestamp: July 24, 2025, 06:21:21 pm
content: Hello Guys. I'm new here. I'm polish so forgive me broken grammar.I am self thought hobbyist and I had a chance to buy Agilent 66311B power supply from someone who tried to move output on the back to front. In the process of putting it all back together he put transformer upside down. This way he connected 220V supply into secondary and as he described 'It blow into his face'. I bought it very cheap and as a I am hobbyist for me it looks like awesome bit of kit. Id love to fix it. What I've done so far is: I checked all PCB connections to transformer. All the PCB fuses were blown, but everything down path from there looked fine; no shorts, no blown MOSFETs. I got it working again. It turns on and reports no Fault. But before putting it back together I decided to put the board under microscope to see if everything else is ok and I found missing component and torn trace. I've got problem with finding any information about it . It is a resistor on main PCB,R485and trace under it. Id love to fix it. I cannot find the schematic or someone who got this equipment and would be so nice and quickly check what resistor it is and what that torn pad leads to. As you can see on the picture there is trace looking like it connects to it coming from the top but I can't be sure... I appreciate any help you could offer. Thanks guys.

author: Swake
author_rank: Frequent Contributor
timestamp: July 24, 2025, 07:28:22 pm
content: Welcome here.Only fuses blown after connecting a transformer backwards is really not a bad outcome.The service manual (attached) does not contain a schematic. It notes there is an older through hole version and a newer SMD version of the mainboard.Found A video about this machine:At 6:33 the mainboard is clearly visible, but is seems to be different from yours. I circled the zone which I believe is the one you pictured on your board.Could you share the board number/version and a picture of the whole board?

author: Swake
author_rank: Frequent Contributor
timestamp: July 24, 2025, 07:42:11 pm
content: Found a video with the same board as yours but can't read what is on the resistor.

author: Swake
author_rank: Frequent Contributor
timestamp: July 24, 2025, 07:57:08 pm
content: I asked the new kid in AI town, because nothing to loose here. Take that answer with a grain of salt.....That said, if this answer is correct and not an hallucination of that electronic brain then this is spectacular.

author: gamalot
author_rank: Super Contributor
timestamp: July 24, 2025, 07:57:47 pm
content: I have a 66319B and I think the circuits are mostly the same. R485 here is 196 ohms and that pad goes to the via as you would guess.

author: aeg
author_rank: Regular Contributor
timestamp: July 25, 2025, 12:20:16 am
content: Quote from: Swake on July 24, 2025, 07:57:08 pmIf you don't like that answer, you can pick one of these:https://www.eevblog.com/forum/chatgptai/the-incredible-shrinking-resistor/msg5989271/#msg5989271

author: Dar_Gol
author_rank: Newbie
timestamp: July 25, 2025, 07:06:07 am
content: Quote from: gamalot on July 24, 2025, 07:57:47 pmYou are absolute Legend Sir!Thank you guys so much.

author: Dar_Gol
author_rank: Newbie
timestamp: July 25, 2025, 09:05:30 am
content: Resistor sorted. When I started it it didn't report any faults but readout was 10.8V and almost 4.5A while output was at 0 (measured 68mV). U305 and Q305 gets really hot really quickly. I think I will follow service manual step by step to try and find out what's going on. I feel so dumb now. I've put thermal camera on main board, all ICs in couple seconds reached over 100'C. Do you think its cooked? Is there a sense to look further?

author: hp3310a
author_rank: Regular Contributor
timestamp: July 25, 2025, 08:24:32 pm
content: Seems this unit may be designed similarly to my 6611C where U305 is responsible for generating the 5V for the digital logic board. It gets scorchingly hot by design (https://www.eevblog.com/forum/repair/6611c-front-panel-removal/msg5981291/#msg5981291).