Electronics > Repair

What more i can do?

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Harry_22:

--- Quote from: 222Lab_Test222 on November 08, 2024, 11:52:22 pm ---
--- Quote from: Harry_22 on November 08, 2024, 11:38:09 pm ---Chеck the signals Chip Enable and Output Enable (please see the picture).
It would be good to compare them with the working board.

--- End quote ---

They are all good, Except there is no volatges in A pins which are input pins in Non working board, Thats the case i am mentioning from the start of this forum.

Other is everything good.

Ps
When I check where some of those pins connecetd they are connected to near tornado IC and few of them to other ICs

--- End quote ---

You have to look the signal at power on by oscilloscope.
Play with trigger function to see the beginning process.
Note: All IC15, IC16 EPROM pins are in parallel except Chip Enable#.

Track the Reset# sinal at pin 8 IC1. It should be low at the beginning and getting high if all voltages are good.
It is possible to use Reset# rising front as a trigger to see other signals at start up.

Could you attach some pictures with start up signals on Chip Enable# and Reset#

Harry_22:
I'll bet a few bucks that due to increased leakage current (DCL) in capacitor C1 (after 30 years it is allowed), MB3771 chip does not release Reset# signal.

222Lab_Test222:

--- Quote from: Harry_22 on November 09, 2024, 06:56:34 pm ---I'll bet a few bucks that due to increased leakage current (DCL) in capacitor C1 (after 30 years it is allowed), MB3771 chip does not release Reset# signal.

--- End quote ---
IC1 8# RESET PIN
I guess it is working fine.
-Connected to IC2 1st Pin
-Connected to IC5 1st Pin

222Lab_Test222:

--- Quote from: Harry_22 on November 09, 2024, 05:15:02 am ---
You have to look the signal at power on by oscilloscope.
Play with trigger function to see the beginning process.
Note: All IC15, IC16 EPROM pins are in parallel except Chip Enable#.


Could you attach some pictures with start up signals on Chip Enable# and Reset#

--- End quote ---

It  seems all ok, both ic15 and 16 have similiar results.


Note : Not sure why images are being rotated automatically.

222Lab_Test222:
Output enable
Yellow is working board.
Blue is non working board.


The chip enable is same on working and not working board.

Note : Does the op enable pins matters as there is no input voltages to proceed.

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