DonNews #14 26 марта 2001

Железо     Pentagon

Repair - Continuation of cycle repair the Pentagon. "

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         REPAIR

 Continue to publish on the topic of repair
PENTAGON-s, but face it - a little digression.

(C) WILD / oHg.

 Somehow slipped past in one of the "KR-NEWS"-s
infa how nahalyavu call from a payphone without a street map. I 
do not know how where, as we have in town to do it easier

(Although, in almost the same).
 Dial any number that can be
Contact Free (01,02,03 ... 000). Waiting
while there will put up. For those not very
rapidly gaining UNIT and just as slowly
its release. Afterwards, the tube signal
invite you to call her parents.
 If your phone is not with the disk, and a touch
dialer, you just need to press
"1." (And if possible, slowly let her go)
 I hope it is someone will be useful, but
Now the promised repair information.



       NO SCREENSAVERS FIRM ON THE SCREEN

              (Continued)

 Just cause could be the closure of the output signal processor 
that is data bus, address bus, etc.  Check out all the tracks 
that are output signals of the microprocessor to its

installation. This should be done as follows (assuming that the 
tires are not hung up on "+5 V").

 Touch the probe of the oscilloscope, simultaneously touching 
her finger.  In this case, because of interference of your 
body, to You should see a sinusoid. If

there is a closure on a common wire, the sinusoid will not. If 
the closure of the "+5", the it will be a constant composes.

 Then check-circuit tester
bus address and data among themselves, as well as
for continuity.
 Check the resistor R21, its face value should be equal to 750 
ohms.  Check the signal CLK at the element

D 13 / 6.
 One reason may be the lack of reference to Rom. Verification 
is performed without Z-80 and Rom.

 Connect the common wire element D13 / 4
(A15), D 13 / 5 (A14) and D 13/19 (MREQ). When
that the element D 50 / 1 should appear
high potential, and the D 51 / 2 - low.
 This signal is fed through a resistor R23
the element D 85 / 2. On D 85 / 1 - also comes
logical zero (MREQ = 0). Then the output
D 85 / 3 will be a low potential for resolution of
sample chips D 36 (ROM).
 Now check the address to the chip
D 54.Dlya this will translate a trigger signal 67 D A7 
(D13/37), so that the element D 67 / 8 was a low potential. 
Then the low potential to appear on the element

D 54/18, and the element D 36/22 - tall,
ie accesses the printer ROM.
 Then translate the D flip-flop 67 in the opposite 
sostoyanie.Togda on element D 54/18 will be a high potential, 
but on the D36/22 - low, ie will appeal to the main ROM.



          KEYBOARD IDLE.

 Probable cause is a lack of circulation to the chip D44; D70, 
or neisprvnost them.

 IC D70 serves as a buffer on the line
communication with the keyboard and constantly open to
output of information from the processor to 
klaviaturu.Protsessor consistently sets the zero level for each 
of these lines, addresses, and even reads the input port 
through the chip D44 for the appearance of zero in one of his 
vhodov.Tak the process of identifying and identifikatsiinomera 
pressed.  To test the chip D70, ocheredizamykayte on its inputs 
to the neutral wire and simultaneously check the availability 
of low- building on its respective output.

 D44 has two chip enable input: D44/1- is switching directions
channels. At lower potential on this pin chip receives data 
from the keyboard.  D 44/19- this entry transfer channels in 
the Z - state (high potential). Since

feet 1 and 19 chips are connected together,
it works on the reception of signals in the presence of IORQ = 
A0 = RD = 0.  To verify, connect to ground (without the Z-80) 
The findings 20,21,30 element D13. When working properly on the 
D44 / 1 should receive a low potential for resolution of 
reading from the keyboard. Now in turn connect with the common 
wire legs 8, 11,13,15, 17 chips D44. and check the appearance of

low capacity at the feet of 12, 9,7,3 chips D 44.