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3-4. CPU PCB Unit
1. Circuit Diagram
To repair the CPU PCB unit, set it in a normal device. (Before setting the CPU PCB unit, confirm
that the CPU PCB unit is not 'trapped.)
Then. check it according to the following nowchart.
CD
~
(3l
@
(5)
@
I.Reset circuit check
TPIOI ...... I02
2.Clock signal check
TP201-204
3.DTACK.IRO check' TP301-302
4.Address decoder check
TP401 ...... 403
5.CRT signal check
TP501-505
6.Memory signal check:
TP601 ...... 603
Refer 10 chapter 4.Check Operation.
7.Ringing .ignol check
TP701-704
8.DTMF TONE check
TP801-804
9.Corrier check
TP901-904
(2) Use self diagnosis to perform the defective block identification.
@) After setting the power switch to ON, perform the sum check for the system ROM. As a result,
"Beep" sounds once (approx. 450 ms) for OK.
If "Beep" does not sound, the ROM sum error or the previous circuit is faulty.
@)
Because the Gate Array
#
I operations are checked visually, the CRT display is turned on and
off. If the CRT display is ON, Gate Arrays
#
I and 2 and Video RAM are normal. If the display
is faulty, the CRT synchronous signal and Gate Arrays
#
I and 2 etc. are faulty.
o
Take the appropriate countermeasure according to the results of self diagnosis.
®
Same as the above
®
If the internal modem is used to generate faulty communications, check circuits 7 to 9. The
main purposes of each element are shown below.
• RA V (arrester & varistor): lightning protection element
• ZD2 & ZD3: Prevents ring-detection malfunctions (Removes noise of less than IS V).
• VZ2: lightning protection element
If voltage exceeding 350 V is applied between CN6 3 and 4, close the circuit.
• SVR I : Controls the carrier to prevent the level from exceeding the standard level when
sending the carrier from the internal modem to the telephone line.
• VRI : Adjusts the DT MF sending level.
l
• VR2: Adjusts the carrier level.
~
Not used
3-35
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