68kMLA Classic Interface
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| Click here to select a new forum. | | 840AV bus transceivers question | Posted by: Betelgeuse on 2026-09-29 17:33:43
Have a non-chiming 840AV board, one of several. This one behaves differently in that there is normal bus activity briefly after power-up and then all goes dead. Looking at the board under thermal shows the 4 ABT245 bus transceivers stone cold. These get warm on my other boards and the VRAM transceivers on this board also warm up. TEA from MCA seems to trip briefly to low before silence.
Is this indicative of bad transceivers or a problem upstream?
Since the board goes dead so early, within about 3 seconds of power-up, I'm thinking some issue with accessing the ROMs. This board also has the ROM SIMM socket but using a ROM SIMM results in the same behaviour. The board was working not long ago. Fully recapped.
I have replacement transceivers but I don't want to replace them unless I have to as the pads on these are super-fragile. | Posted by: Betelgeuse on 2026-09-29 23:11:43
To answer my own question, one of the transceivers was bad, plus bad RC10 diode array (shorted on pin 14 to GND for line D10). Now the board gets further and bus activity does not go silent quickly but still no chime nor display... Sigh... back to the drawing board (pun intended). | | 1 |
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