Electronics > Repair
Fluke 289 not quite sorted.
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booyeah:
I'd like to say a massive thanks to everyone in this thread.

A couple of years ago I decided to make a lipo battery circuit for my 287, I either reversed the polarity or possibly over volted the battery inputs. Anyway the end result was a dead meter with just the five power button flashes. I had a go at troubleshooting but got nowhere, so it's just been sitting in a drawer ever since.

After following this thread, I decided to have another go at fixing it.
There was a short on the MXS 3v rail. Testing with an external supply caused the CPU to heat up. So I ordered a replacement and had a go at soldering it with a cheap ebay hot air gun.

I couldn't do it as the lead free solder paste just wouldn't melt properly. I hand re-balled the chip with some leaded solder and thankfully it worked this time. I then edited the MXS boot script using an Arduino as a serial pass through. Success, my 287 has come back to life.

Something to note is how delicate/finicky the lcd flex can be.
Initially I thought I had damaged the lcd as well, as it was very faint on booting. The fluke logo would show faintly them fade to nothing. I tried it on another meter with similar results, sometimes there were graphical lines missing as well.

I checked all of the connector pin voltages and signals, they roughly agreed between the two meters. I tried re-seating the connector, cleaning etc. I found that applying a little bit of pressure to one side of the flex connector fixed it, so I tinned the pads a little bit and now the screen works perfect.

booyeah:

--- Quote from: MihaiV on December 18, 2021, 05:29:09 pm ---Hello again,

The SL10327 arrived! The part appears new, in the tape, with no traces of removal from other equipment.
Swap it in and... nothing.
The problem is somewhere else.
Don't know where else to look at the moment...
Could it be a problem from the MXS or the RAM? Could the start-up logo be displayed from the ROM and when RAM operations start, everything goes wrong?

--- End quote ---
In an earlier post you checked the lcd pins. Is it possible the solder connections to the cpu are damaged / cracked?

My    287,     289   lcd connector
1  20.349   21.19
2  19.017   19.88
3  17.83     18.56
4   2.525     2.637
5   1.272     1.32
6   0            0
7   0            0
8   2.953     2.931
9    pic 1
10  pic 2
11  pic 3
12  2.953    2.934
13  pic 4
14  pic 5
15  pic 6
16  very busy like pic 6
17  very busy like pic 6
18  0          0
19  6.986    6.98
20  4.758    4.69

Pins 13-17 were very busy non repetitive signals so hard to capture, but you should be seeing some activity, not 0 volts.
MihaiV:
Good evening booyeah,

Thank you for the scope captures! There is a ton of signal missing from my LCD lines!
I will check them again in case I missed them somehow.
I took pins 19 and 20 as backlight circuitry, with Q17, Q18 and Q18 part of the intensity adjustment. There is nothing there too.
I will try to reverse engineer that part and come with a schematic.
Was your backlight on?

I also fear(ed) that there is a solder joint cracked somewhere. In fact, the meter was rarely showing the start logo. I noticed that it worked constantly only when pressing near or on the MXS. I reflowed it once with some equipment at university and it booted every time since then. Also reflowed RAM and Flash while at it.

Also, the MXS crystal was not oscillating at all (but it was still showing the start logo). I changed it with something from the junkbox, and now it oscillates nicely (pics in a previous post). Changed nothing though.

Broken joints and a possibly cracked crystal could indicate a healthy mechanical schock (although the case is like new).
One thing I could try is to reflow the MXS again and gently move the part while in liquidus phase (with a bucket of flux). Maybe the cracked joints are oxidated and did not allow the solder ball to regain continuity. I have seen that before in other equipment.
Will return with updated status on those LCD lines.

Thank you,
Vidrascu Mihai.
MihaiV:
Hello,

Back with the LCD pins scope captures.
My final pins are definitely silent (see attached pictures).
I used the low(er) capacity probe at work to also check the crystals of the MSP and MXS, also in the attachments.
I did not manage to reflow the MXS yet, no spare time at work the last days.
Anyway, isn't the LCD communication unidirectional? The meter should work (beep at button push or at continuity test) even if the screen is detached (or with a faulty solder joint).

Happy Holidays!
MihaiV.
MihaiV:
The remaining scope captures, attached below.
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