Electronics > Repair

Fluke 233 could not start properly

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antyvirusa:
Hello everyone,
I am new to the forum, but already read a lot of topics here. My problem is that I recently owned non working Fluke 233 and can not make it to work. When I switch the rotary switch position there is only red led flashing and ---- (four dashes) showing on the display. It did start properly one time and I tested all functions except current measurement and all were working pretty fine, but this happened only one time (maybe I already tried hundreds or thousands times switching it off to VAC- the first function). The thing that I know, whenever it start properly the attached display is showing only dashes and is working only via RF (I think this may be optical problem between the body and the display). When it started properly the red triangle turned off and was not flashing. Anyway whenever I start it now the red triangle flashes and display only shows four dashes, when attached or RF ERR when not attached. The display is only turned off and on by the body when attached.
The consumption of the body is surely less than 1mA as my power supply can show mA (I test it with power supply, not with batteries). All resistors on board are tested and in working conditions. Inductors checked for continuity and are okay. No shorted capacitors also. MOVs and current sense resistors are also fine. The rotary switch looking fine and steps with about 0.30V between positions. Voltages +2.5V, -2.5V, +0.8V seems fine also. I already resoldered every pad/pin on the PCB including the microcontroller, ADC (LTFLK2) and RF (13201), also checked for short circuits and there are none. I checked the SPI lines (I think that they are SPI, checking the datasheet of the microcontroller) and are all in HIGH level while in VAC position, no clock, no data I can see on the scope. I also cleaned the board with Isopropyl Alcohol.
I think it stuck while booting and could not go on. Maybe waiting for some signal...
If anyone could help me, I will really appreciate this. And if someone could tell me if the body could be started without the display attached (the red triangle to be turned off) I will be thankful. As I read in the user manual this is possible and this is not a fault in my research as I switch on and off the body without attached display. Also someone with working Fluke 233 DMM if could measure the test points on the board will be a big help. I attach PCB pictures (the burned looking paths are from very bad flux that I can not clean).

sunfire:
/deleted

Ugur:
Most likely your problem is with the video card.
Did you change the batteries of the display?
If yes, is there any bad contact or oxide on the board?
You can freshen the solders.
The optical sensors in the display module may be faulty.
This problem should not be caused by the motherboard, have you had the opportunity to try with another screen?

antyvirusa:

--- Quote from: Ugur on February 02, 2023, 05:56:29 am ---Most likely your problem is with the video card.
Did you change the batteries of the display?
If yes, is there any bad contact or oxide on the board?
You can freshen the solders.
The optical sensors in the display module may be faulty.
This problem should not be caused by the motherboard, have you had the opportunity to try with another screen?

--- End quote ---

Thank you very much for the reply.
What do you mean with the video card (what is video card here)?
Yes, already changed the batteries, also tried on external power supply. I know for the battery leakage problem with older firmware (mine is v1.1).
I freshened MCU solders, but still nothing.
The optical sensor is probably faulty and I will check these, but I think the body should start without display and the red high voltage triangle should switch off when MCU boots properly and ready to make measurements??
Unfortunately I could not find someone with the same DMM in my area to check with another display..

antyvirusa:
Another thing that I forgot to update is that I found that pin 70 - MOSI pin (probably used for SPI, as it have connection with a pin of the external ADC) is floating. Whom is the responsibility to pull this pin - the master or the slave? (I think maybe the slave should pull up this pin after low level on CS and then master's output should drive this??) All other SPI pins (CS, MISO, CLK) are logical high in the same time and I can not see any transitions in any way. Any help will be appreciated.

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