Cutting a trace to find a faulty component(?) in an HP3312A function generator - Page 1
Forum section: electronics / beginners

author: Grey_Dawn_Breaking
author_rank: Newbie
timestamp: July 06, 2025, 12:24:14 am
content: Hi all, I have an HP3312A function generator that is acting oddly. I tried watching some tear down videos online to get an idea on the kind of troubleshooting work I had ahead of me. I came across the following video where the tech mentions cutting a trace to narrow down the area where his faulty component(s) could be. He does it at the 4.13 mark and then again later at 5.27.https://youtu.be/N4dDpmDjUrQ?feature=shared&t=253Can someone explain to me what exactly he's doing? He's cutting the trace and then...what? Is he running voltage through it? Is he seeing if things act better in other parts of the unit? I have no idea as to what he is doing nor whyAny insight would be appreciated!

author: edavid
author_rank: Super Contributor
timestamp: July 06, 2025, 02:00:58 am
content: I didn't watch very much, but I think there's a power supply short that he is trying to isolate. If he cuts the trace and it's no longer shorted, he knows the short is somewhere beyond the cut.I don't see how that's relevant to your HP 3312A. If it's working well enough to be "acting oddly", it probably has all the power supplies working.Most 3312A problems are caused by the interboard connectors. Try separating the board sandwich and plugging it back together a couple of times (use contact cleaner if you have it).If that doesn't fix it, tell us what the actual problem is.

author: indeterminate
author_rank: Regular Contributor
timestamp: July 06, 2025, 03:23:11 am
content: There are jumpers that you can remove for isolating the power supplies.The last one i fixed needed a few of the linier voltage regulators replaced and a couple of the zener protection diodes on the power supply rails.as well as the usual electrolytic caps.a thermal imaging camera or just your fingers can show you hot spots and potential problem components.HP where pretty good at locating jumpers at locations where you might need to isolate sections of the circuit.cutting traces in my opinion is a nono

author: Grey_Dawn_Breaking
author_rank: Newbie
timestamp: July 06, 2025, 02:19:32 pm
content: Thanks for the info all. Watching that video was just a preliminary and I was curious as to why he was doing the trace cuts.Once I open it up and start poking around inside I'll start a new thread on the issue I'm having with my HP3312A. (To be brief: the vernier amplitude dial doesn't seem to be working the way it should - I'll start a new thread once I've given it a better look).

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: July 07, 2025, 06:10:50 am
content: I had a PCB to repair the other day...had short cct on input voltage rail, blowing 5A fuses. The best way to identify the culprit was to halve the cct which unfortunately meant cut some PCB traces. The input, want thru fuse to: qty 2 separate buck converters (to produce 3.3V the other 5V) and also to a H bridge drive as Vcc (and some electro's on this rail). I kinda already knew it was the H bridge ....but cut the Buck traces anyway....sure enough it was the H bridge. Its just that its a PowerSO package, so R&R this to check its ridiculousYes you can (if you have one) use a very good sensitive low ohms meter, the closer you get to the Short cct the less resistance...but all depends where you put the other probe as well and this had top/bottom and internal GND lines!Alternate was inject very low voltage at a Constant current limit....and follow the hot part but my PSU just dint like this. This method failed as it was dead short cct, however, I could have wired a car bulb (system was max 18VDC in) in series to the power line to give it some load and act as a NTC resistor. But this could still possibly burn an inside layer PCB trace, which i didn't want to do.I don't like doing cut traces, if i can avoid, i generally do, like lift IC pwr legs. Anyway FWIW.