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Understanding this circuit diagram of AK-700 telephone


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hi friends my name is walid from Gaza strip, first of all I am new in this great website and 50% in English language and love passionately electronics. I am interesting in circuit design analysis than build it i think that if u understand u assurance can build so i want to understand the circuit diagram of AK-700 telephone from:
especially Q2, Q3 and related components i want a detailed discussion about each element in the circuit, i go to many many websites for help and back to some textbooks and asking some people but no results.
Please someone help me, thanks.


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Hi Walid,
Welcome to our forum. ;D
I think Q2 and Q3 are used to turn-off the supply voltage for Q4, for rotary dialing pulses.
When PO (pulse output?) goes low for a dial pulse, then Q3 turns-off which turns-off Q2. With Q2 off then Q4 doesn't have a supply voltage and doesn't draw current. Without Q4 drawing current and nothing else in the phone drawing much, then the phone is considered to be off-hook for a moment which is seen by the central office as a rotary dialing pulse. ;D

Years ago I was working in a building under construction. I got locked-in. There was a rotary dial phone but it had a lock on the dial. I tapped on the hookswitch to dial for help. After many tries, it worked! ;D

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hi audioguru thank you very much for the useful informations u gave me and i have another questions as:
1- datasheets of hm9102
2- when someone talk near MIC, i think that voice signal  go through C7 to base Q4 then through the power line to the collector of Q2  at this point i cant understand, is Q2 is a common base amplifier or something else ..... what if Q2 is NPN type
3- i read that voltage between tip and ring lines is 48VDC, why they are 8.3 VDC at point A in the schematic.
4-is Q2 function as a pass transistor regulator inaddition to its function as a control device 

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hi i have an extra equestion
can anyone tell me about how the signal pass from MIC through C7 to first amplification stage Q4 then passing small part of this signal to speaker through Q5, now how this signal reach the telephone lines to the caller side, how it pass Q2 and what about the rectifier bridge

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