Electronics > Repair
SUCCESSFULLY REPAIRED-Hameg hm5006
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Harry_22:
The controller TDA4605 is locked with a latch of T1009, T1011 transistors.
This is indicated by the low voltage 0.5V on pin 3. (T1009 shorts pin 3 via R1059)
A low voltage on pin 6 indicates that the controller is leaving the switch-off state but does not start up because it sees "mains undervoltage" via pin3.

The latch is switched on by the high current via sense resistor R1015.
If your PS turns on after several attempts to put and remove the plug that means it isn't shorted but little bit overloaded.

Try to disconnect PS from SA and test it for instance with 100 Ohm 6W load between +12V and -12V rails.

Be careful with P1010 connector!
vlelectroniclab:
hi,
i removed the power supply from the instrument and started everything and it has the same problem.
i checked all the current detection part, the two transistors, the resistors and the capacitor and all the components are good (to check them i unsoldered them).

i did a trivial test, instead of 220vac i gave it 24vdc with the positive that powers r1019.
on pin 3 i put another power supply and gave it about 2v and i heard a buzz, all the voltages are ok.
after this could the tda be faulty?
Harry_22:
Good job!

You can connect 100k in parallel with r1050, r1048 to get 2V at pin3.
TDA is Ok.
Check C1040, C1041. They provide a soft-start delay.
vlelectroniclab:
hi,
sorry if I didn't update you, but unfortunately I didn't have time to do other tests.
c1040/1 are good.
i tried to put the 100k resistor but the voltage is always low, it seems like the tda pin absorbs too much current...
i had a doubt what is the difference between the tda4605-15,tda4605-2,tda4605-3?
Thanks Vito
vlelectroniclab:
Hi,
Finally I solved the problem.
To be safe I tried another tda but nothing worked. then I increased the voltage at pin6 of the tda to 12.3v with a power supply and magically it turns on.
I replaced the R1030 with a 470R and now it works perfectly, it starts on the first try and the voltages remain perfect.
From what I understood is that someone had changed the original TDA4605 with a TDA4605-15, it just absorbs a few more mA and the supply voltage does not reach the starting threshold.

Regarding the display that no longer worked I adjusted the contrast via R1003-R1004 and it appeared.

All in all I have to say that it is a good tool for the time
I will use it mainly to see if the 433mhz radio controls work and for now it is enough for me.
Thanks to all of you for the tips.
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