DonNews #13 01 января 2001

HARD - Extension publications repair PENTAGON-s.

          HARD


 We continue to publish recommendations on
repair "PENTAGON"-s.



     Do not I see the chess field.

            (Continued)

 A possible reason may be the fault of address multiplexer 
D16-D19.  Elements of the D18, D19 pass on chip

RAM address from the processor and the elements of D16,
D17-of videokontrollera.Ih check is done without the Z-80, ROM 
and OZU.Obrezhte signal C-23, which is removed from the element 
D15 / 5, or set the trigger D15 in this state, the signal C23 
was high. Then the elements of D16, D17 will move in the 
Z-state, and the D18/15 and D19/15 through D51 / 6 goes low 
capacity, and D18, D19 open for data transmission.

 To test the elements of D16-D19, trim
signal C14 (RAS pulse of D45 / 3), reaching
nA 1 st leg of D16-D19.Za to provide for
15-feet x D16 and D19, or D18 and D19 (in pairs), by a trigger 
on the D15, low voltage circuits urovnya.Togda D16, D17; or 
D18, D19 (in pairs) will be opened for Broadcast dannyh.Teper, 
feeding on the 1-e legs items D16, D17 (D18, D19) 0 or 1,

Check the direction of the signals
through these Products:

HIGH-CAPACITY LOW POTENTIAL


   D16 / 1, D17 / 1 D18 / 1, D19 / 1

 Input Output Input Output


  3 - 4 2 - 4


  6 - 7 5 - 7


  10 - 9 11 - 9


  13 - 12 14 - 12

 Passage of the signals can be viewed in
dynamics, when the transition is
pulses RAS.Dlya check D18, D19 can
use any pulse signal video controller, feeding it through a 
socket Z-80.Mozhno checking and clipping wires, and simply 
closing the entrances to the building multiplexers, and observe 
the appearance of negative pulses at a vyhode.No

test requires a practical skill.

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      NO COMPANY screensavers on the screen.

 One reason may be the fault
buffer register D39, or the lack of reference to him.
 Verification is performed without the ROM, RAM, and Z-80.
Connect to ground elements: D13/19
(MREQ), and D13/21 (RD). As a result, the element D39 / 1 
should receive a low potential, and the need to be D39/11 
impulses. Until the voltage on the element D 39/11 high-level, 
data D0-D7 are displayed on the vyhode.Podachey D 39/11 to a 
low-level allowed entry into the chip of the new

bytes.
 The logic of the work to understand how to check
chip, but it is simpler to use
For this test ROM.
 If you run this test if the element D39
faulty message appears: "Faulty
buffer to read data. "


 P.S. If anyone interested in informations on
the principle of the ZX-SPECTRUM-PENTAGON, then
please, it can be very useful.