No Sound. Signal at output of SN76477 pin 13, follow through to input of sound amp, then from output until we reach electrolytic capacitor used to decouple connection to speaker. Signal going in, nothing coming out – replace capacitor sound back to normal.
Only drawing a few pixels of player balloon sprite. Following the schematics, the sprite data from the eprom goes into a 74LS166 shift register at H3, output from this looked suspicious. Replaced this and sprite back to normal.
Blank screen, Blanking line to output colour proms always enabled. Trace back to 74161 in timing circuit – output stuck, input clock all look OK – replace chip and picture appears. Blue video only – The video lines are controlled by three transistors near the edge connector, checking these revealed that 2 were not giving…
Glitched graphics. Screen changes as board is flexed. Moved around board pressing chips until pressing the custom surface mount chip at B6 changed the effect. Noticed that the corner most pins had come up from the board. After an unsuccessful effort to resolder them, I used some enameled 38 swg wire to solder from the…
Carnival on a Gremlin / Sega Vic Dual PCB. Just had blue bars on screen, although probing the Z80 showed it was trying to run code. Using a logic probe I discovered that the /WRITE signal of the ram chips was always high. This signal comes from a 74LS10 at U77. Checked this chip and…
In normal mode, just had a blank screen. Enable test mode and you instead get an error message showing that the ROM test had failed (even though the rom itself checks out OK with correct content) This is because the custom Atari SLAPSTIC chip is not functioning correctly. It is used to page banks of…
Capacitor burnt. (game board), particularly at C37 the capacitor was showing signs of extreme heat. Replaced them all with 22uF 25V axial electrolytics. No Speech / Some SFX missing. (game board) Output from speech chip SC01 was OK, as was output from IO Custom (X3). checked transistors in output stage and 2N4401 was faulty. (Q2)…
Ran through self test OK, came up with chequer board screen and then reset most of the time. Occasionally would start game, but with credit noise continually playing and credits rapidly counting upwards. This is caused by CPU 4 (E5) not running properly. checked the eprom and ram (C5,D5 and E5) and ram was faulty….