Fluke 87, Dead, chirps sometimes

[iblackford]

Hi All,

Apologies if this or a similar problem has been covered already in an existing thread. I have done some searching, and I haven't found this issue.

Symptoms on my Fluke 87:
-Unit is dead, no display, no beeping when trying to do a continuity test in the ohms position (yes, I tried pushing the speaker button to enable the beeping)
-There is a slight "chirping" that I can hear when switching modes.
-no backlight

Things Tried/Measurements taken:
-Resoldered the 9V battery connector as it looked suspect. No Improvement. Verified that 9V is present on the PCB
-Checked VDD to U4, and it's present (~3.2V, relative to VSS)
-Checked that the oscillator to U4 is running

Questions/Further Actions:
-U4 (main custom ASIC) seems suspect to me, given that it drives everything (backlight, speaker, display...) what other things can I try to rule out before assuming it is U4?
-There is a "TEST" mode for U4 referenced in the service manual. Does anyone know how to initiate this mode?
-Are there any options to purchase U4 (SPX-87) or similar equivalent IC?

Thanks in advance, Ivan

[shakalnokturn]

A couple of thoughts as you have already done most of the routine checks I would have recommended.

I haven't been out looking for the schematic so some suggestions may not apply.

Check current draw, some flukes have the buzzer driven by CMOS logic permanently supplied from battery. Sometimes the IC fails and drains the battery fast. I doubt it would give your symptoms but measuring current can still give you some clues on what's going on or not.

Check / clean function switch contacts, some models use a carbon coating that wears away and causes trouble.

If there's a SPI or I²C serial memory check bus activity.

If all else fails try reflowing the TQFP's I've had more than one Fluke meter acting funny that behaved after resoldering.

[coromonadalix]

have to play with the rotary dial on one of my 87 at the job

Play bonkers,  beep for nothing, display stuck  etc ...   have to rotate it as few times and get it to work,     yeah i'm lazy to open it and clean and lube the dial contacts, maybe they are used up to a point,   theses meters are intensively used ...