Help identifying a component: 2 types (solved: MAX708T, MBRS340)- solved - Page 1
Forum section: electronics / projects

author: Nexxen
author_rank: Regular Contributor
timestamp: June 13, 2023, 11:55:40 pm
content: Hello!!One has a f040 mark. From left to right: ~10K ohms; other way round ~1.65K ohms.The other has a 70BT CUA marking. Can't figure out what's it for.Edit: could be 708TSee pictures as they are better than my words.Thanks for any help!

author: MLXXXp
author_rank: Frequent Contributor
timestamp: June 14, 2023, 12:19:13 am
content: The two leaded one marked B34 is a MBRS340 Schottky diode.https://www.mouser.com/datasheet/2/149/MBRS340-889504.pdf

author: Nexxen
author_rank: Regular Contributor
timestamp: June 14, 2023, 12:57:25 am
content: Thanks!The fact that have resistance measured as I posted (10K in one way and 1.65 on the other) mean anything?I should have 0? Or it means I have to desolder it for correct measures because it's in a circuit?Silly question

author: amyk
author_rank: Super Contributor
timestamp: June 14, 2023, 01:25:20 am
content: The other one may be MIC708TMY.

author: moffy
author_rank: Super Contributor
timestamp: June 14, 2023, 03:33:37 am
content: Quote from: Nexxen on June 14, 2023, 12:57:25 amThe difference in values suggests a working diode, conducting in one direction but not the other the 10k could be the rest of the circuit, but to be really sure it is best to measure it out of circuit with a DMM on diode mode, but try it first with the DMM on diode mode in circuit.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: June 16, 2023, 01:22:01 am
content: Quote from: amyk on June 14, 2023, 01:25:20 amA MIC708 doesn't seem to match the PCB connections, though.Pin 6 is N/C for a 708 but the PCB has a trace going to pin 6.VCC and GND are on 708 pins 2 and 3 but the PCB has a thick trace that is likely VCC or GND, based on what looks to be a bypass capacitor on the same trace, going to pin 4.It might help to see the other side of the PCB and a description of what the PCB is for.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 16, 2023, 02:19:03 am
content: MAX708R/S/T +3V Voltage Monitoring, Low-Cost µP Supervisory Circuits

author: Nexxen
author_rank: Regular Contributor
timestamp: June 16, 2023, 12:56:14 pm
content: Quote from: MLXXXp on June 16, 2023, 01:22:01 amI'll desolder the chip and post pics.

author: Nexxen
author_rank: Regular Contributor
timestamp: June 16, 2023, 12:57:01 pm
content: Quote from: ArdWar on June 16, 2023, 02:19:03 amIt looks like it, gnd corresponds.I'll take readings and post back results.Thanks!

author: Nexxen
author_rank: Regular Contributor
timestamp: June 16, 2023, 01:42:42 pm
content: https://pdf1.alldatasheet.com/datasheet-pdf/view/170484/MAXIM/MAX708R.htmlIn part numbers there is a 708T CUA: MAX708TCUA, 0°C to +70°C, 8 μMAX.(ArdWar, did you just know or you have skills finding stuff?)If it malfunctioning, it could be issuing a RESET pulse constantly?Am I to expect the RESET LED of my POST card to be off onstead of on?Could this prevent the system even to POST at all, thus not allowing any activity and no POST codes?There is a split moment where I can see a FF 00 instead of -- -- (like it can do something between two RESET pulses).At this point this is my best guess (I'd like to say hypothesis but it'd be a stretch).

author: Nexxen
author_rank: Regular Contributor
timestamp: June 17, 2023, 01:36:48 am
content: I removed the 708T and now the board doen't turno on at all, before it would turn on as soon as power was on (on switch of the PSU).Wouldn't accept any reset or even power off after 4 seconds of pressing the power button.Update:If I touch pins 6+7 it actually powers on without the 708T.Pulling the plug, too much time for a board that is underwhelming. Someone asked me why but I think I have my answer and I'm satisfied in boxing the thing among the scrap parts unless anyone has a solution I'm calling it on troubleshooting. I'll order a spare and that's it, if it doesn't revive I'm happy anyway.Thanks for the help I got, as always amazing

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 17, 2023, 06:49:03 am
content: Quote from: Nexxen on June 16, 2023, 01:42:42 pmThis one is actually easy since part number is actually written on the package and surrounding traces kinda give away what kind of circuit it supposed to be. Search engine (Octopart, or even Google) is enough.For smaller packages like SOT235, SC70 or similar it'll require much more context to figure out.

author: Nexxen
author_rank: Regular Contributor
timestamp: June 20, 2023, 01:18:08 pm
content: I soldered the old 708, by pushing hard enough (not too much) the board powers on.At this point I'm pretty sure that this chip failed internally, but without a short, as I'm guessing it has no issues with Vcc and Gnd.If I short PFI+PF0 I can make the board power on. Don't understand why, that's my real question here.https://pdf1.alldatasheet.com/datasheet-pdf/view/170484/MAXIM/MAX708R.htmlI measured Vcc without the chip, 3.66V. With chip soldered it goes down to 2.59V. Looks steep to me. Just curiosity.Thanks in advance for any answer on this one.

author: Nexxen
author_rank: Regular Contributor
timestamp: July 28, 2023, 10:46:38 pm
content: Replaced the board now works 100%It got unstuck from reset and could POST.Last trick, ram wasn't compatible, but when you see codes and hear beeps you don't care.thanks to everyone and everybody!!