Hi Costas,
Happy new year.
I still need to buy a DSO and a disordering station with a vacuum pump (the others (solder wick, heat gun) do not work for me, I screw up the stuff I disorder), besides that I will also need a programmer (which adapters should I buy?). I realized that.
Sure, please tell me your strategy as you have realized a successful repair.
If you have to buy all that just to fix a DMM does not deserve , better buy a good DMM.
Is good programmer from BATRONIX , for beginners good one with 32-pin socket .... but in the future the 48 pins cover several new flashes at 1:1 universal adapters that you can use , much cheaper or easier to built. For the first few adapters you need: PLCC32 to DIP32, PLCC32 to DIP28, SO8 to DIP8, SOP28 to DIP28 .
Generally large my repairs method without schema is simple :
1. looking on the net as much documentation with error coded block diagrams, interpretation of error codes etc..
2. see what kind of ICs is designed device , search and list the ICs pin configuration, so I know which pins is for supply , which pins is for the communication bus , which is input pins output pins ... etc
3. Make copies of all flash and eeprom to restore if something happens on the software side.
4. take measurements on the power pins to each integrated circuit, with the oscilloscope check whether or not the supply voltage ripple.
5. with ESR-Capacimeter check electrolytic capacitors values in circuit
6. with oscilloscope check digital signal amplitude on the ICs imput-output pins , bus terminals, swing on microprocessor X-tal.. etc
7. concluded and try locating defects parts
where are you from ?
WBR Costas