Question about unmarked resistors for camera repair - Page 1
Forum section: electronics / repair

author: jerb
author_rank: Contributor
timestamp: January 18, 2019, 09:48:45 am
content: So i know this may sound silly to some. But are some of those tiny unmarked black resistors ever just there as a jumper? Or is any time one is open (diode test) then is that resistor bad? i'm trying to trouble short a pcb for a camera but i can't seem to find why i'm not getting power. The board has a BD8357 Power controller chip. I replaced a burned out diode just above the PWM chip but i'm still not getting anywhere. Any advice is appreciated. thanks.

author: PKTKS
author_rank: Super Contributor
timestamp: January 18, 2019, 09:59:40 am
content: Some time ago I had similar doubts about a plethora of (some) markedand (some) unmarked "things" on some boards...https://www.eevblog.com/forum/repair/smd-fuse-or-resistor-marked-as-0-(zero)/msg1928416/#msg1928416The answers are almost uniform in that JUMPERS are still alive and wellin the form of those parts... (e.g. VIAS DID NOT RETIRED JUMPERS...)Nevertheless I had a closer look in other boards where some UNMARKED partswere just COLOR CODE BASED. (green yellow blue...)My attempts to understand SMD codes are still unresolved...All the SMD references are damn confuse were labels can be anythingfrom transistor to resistor or just in those cases - nothing. a plain jumper.Considering that you really find that particular code defined...On the other hand ... old school parts are very well marked and definedI have spent a lot of time with that sort of problem...with a box of "parts" just undefinedor with a label you just can not find anywherePaul

author: jerb
author_rank: Contributor
timestamp: January 18, 2019, 10:13:23 am
content: Yeah, I haven't been able to find any good information about it anywhere. The Resistors I'm looking at on the board i'm working on are about 1/4 or smaller then the size of those standard 0 jumper resistors. So there's definitely not enough room to write any sort of number code on them. I just wonder if there's any way to tell a fried unmarked resistor from just a standard little jumper.

author: JackJones
author_rank: Regular Contributor
timestamp: January 18, 2019, 10:16:33 am
content: You can usually tell a 0 ohm jumper from its placement and by the fact that it has traces running under it. You'd need to post a picture to get a more definite answer.

author: jerb
author_rank: Contributor
timestamp: January 18, 2019, 10:45:14 am
content: So the first photo shows the two resistors in question. Both of them show 0 resistance. They're not grounded. Just open. the second photo is the Diode i replaced above the pwm chip. i'm hunting around for bad components because i can't find any shorts to ground but i'm still not getting any power.Edit: This is actually the motherboard for a Leica Q typ 116. So unfortunately and fortunately these are the only photos currently that exist of the internals of any leica Q on the internet. yay me.

author: JackJones
author_rank: Regular Contributor
timestamp: January 18, 2019, 11:07:16 am
content: Those don't really strike to me as jumpers. The lower one is in series with a cap going to ground, so it might be part of a snubber. The resistances in snubbers are usually pretty low, so it might look like close to zero ohms when measuring.Everything else on that picture looks ok to me, nothing seems out of place at a glance.You'll just have to measure the voltages starting from the input and try to pinpoint the problem.

author: jerb
author_rank: Contributor
timestamp: January 18, 2019, 11:15:59 am
content: I'd love to be able to measure voltages but i can't power up the board without it being plugged into the body and when i try to get any voltage measurements on the top side of the board i'm stumped. I can't find any sources of power other then the 8.2V that is being fed directly from the battery in the the top connector. Do you think it's possible that even without any shorts to ground my PWM BD8357 could be borked?Edit: I swapped the PWM Chip. Nothing. Exact Same Thing As Before. no change in readings at all, so obviously chip wasn't the issue. or maybe the chip i used magically went bad while transferring it

author: jerb
author_rank: Contributor
timestamp: January 18, 2019, 02:48:05 pm
content: I figured it out!, Seems like there were two damaged resistors on the left side of the board. One was cracked in half and the other wasnt making contact with the board. Thanks for everyones help!

author: vk6zgo
author_rank: Super Contributor
timestamp: January 19, 2019, 03:18:28 am
content: If you want to check resistors, use the ohms range--- diode test gives weird results if there are any semiconductor junctions attached to the circuitry.