EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: nurvus on November 24, 2022, 03:24:19 pm
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Hi,
I recently picked up a non-working Fluke 115 that ended up having very obvious signs of water damage... It did not power on at all when I first got it and after repairing various traces that had been corroded through, I got some signs of life back. The LCD is showing some characters when turned on, but does not show any of the actual numbers on the LCD or the bottom indicator bar that moves when measuring. The backlight button turns the LED on/off, pressing buttons gets beeps (even though nothing on the LCD indicates changes in modes/ranges). It does seem to be doing something as the ranges in ohms changes from k to M to ohms, just no numbers show. Maybe its not, I don't really know. It may be irreparable, but I think I found more faulty component(s) that I may try to replace to see if I get any further signs of life.
When I removed the metal shielding, there were burn marks right above the Q9 and q10 area in the picture attached.
After googling and looking through posts in this forum, I think I have identified Q10 with marking "M1L 2" (with the 2 being sideways) as MMBT6429LT1 with datasheet here https://www.onsemi.com/pdf/datasheet/mmbt6428lt1-d.pdf (https://www.onsemi.com/pdf/datasheet/mmbt6428lt1-d.pdf)
Q9 is the one I need help with. It looks like maybe it is the same as the part IRLML6302 (Q7) from the post below, but I am not 100% sure, as the one pictured starts with "CJ.."
https://www.eevblog.com/forum/repair/fluke-179-repair-info-incl-partial-parts-list/msg4160173/#msg4160173 (https://www.eevblog.com/forum/repair/fluke-179-repair-info-incl-partial-parts-list/msg4160173/#msg4160173)
The marking on mine is "CGJC0" (or O).
If Q10 was identified correctly as an NPN transistor, it is not testing as working with a multimeter in diode mode out of circuit. IF Q9 is also an NPN transistor, it is not testing as working either. When connected to a power supply the pcb is not drawing any current unless the LED is on or I press a button that makes the speaker beep, so maybe a sign that there are no shorts (or shorts found yet). Not sure, but focusing on Q9 and Q10 first. Miraculously, the resistors nearby measure fine out of circuit, even though some will need replacing because the contact on one side looks nearly corroded through, but voltage is still passing through them.
Thank you for any help in advance!
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Yur guesses are correct
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Thank you very much!! I have the components on order.
Is the component parts list you referenced available online? I was searching for something like that - I found one for an older model Fluke but not similar enough to be of much use. I found a couple of caps that have one terminal/side corroded through and would like to look up the values to replace if there is any progress made after replacing q9 and q10. Same with a couple of unmarked resistors. Either way, thank you kindly for confirming the components in my OP.
Hope all is well and take care.
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Hi, just wanted to share an update. I ordered and replaced Q9 and Q10. I also had to replace R20 with a resistor of the same value I pulled from a scrap board.
Unfortunately, after taking the LCD out I noticed the traces on it had also suffered water damage and more than half of the traces had been worn away, hence the reason only some things were showing on the LCD and not everything. I ordered a replacement LCD from AliExpress for about $21 US shipped and with that replaced have been able to make more progress and test.
So, the next project is the dial/selector with the metal contacts. There are 4 total contacts in the selector and 3 of the 4 are broken. I have tried searching for just this part online with no luck, but I am more interested in seeing if I can possibly fix the one I have... I was able to still test a few modes (continuity, diode, capacitance, resistance) by soldering wires to the appropriate contacts on the wheel pictured, and those seem to be working fine. I still need to test the rest of the modes (voltages and amps, both AC and DC and millivolts), but feeling hopeful. We'll see.
If anyone has any suggestions on possible ways to "fix" the selector contacts, I would greatly appreciate it. I will attempt to use some scrap metal I can cut and bend into the right shape to see if I can wedge and secure in place.
I also wanted to see if anyone could help identify the value of cap #18 (C18)? The one side of it has completely corroded away so I cannot measure it to try to find a suitable replacement. The modes I have tested so far seem to be working without the cap but would like to replace it if I can and not sure if not having it will impact the other modes I still need to test.
Also, above the contact wheel in the picture, there is marking of "S1" above a trace that connects 2 pads (circled in red in one of the pictures). It connects 2 pads, but on mine the pad on the right side is gone and no longer attached to the trace or via. I will also attempt to repair the pad, but was wondering if anyone knows a) what is is for and b) if it is needed?
Sm233, thank you again for your help in identifying the previous components! I would not have gotten this far without your help!