![]() ![]() ![]() It also appears that there are some cycles when the data bus is fully released - I had been seeing lower pulses only a bit over 4V, but they seem to be occurring when nothing is actually driving the line, so it's sort of a parasitic pull-up. I will try both side by side with a functional unit when I can get it working, but at least right now the symptoms are the same using either chip. I also thought I had a glitch chased down to the MB8873H we had very little information on, but through matching some pinouts and searching around with MPU compatible chips, I think it's functionally the same as the much more common HD6840P PTM. ![]() Thanks to a bit of paint and a strange part number, one DIP 8 on each side is the LED driver, a TA8513P, marked TOIC8513P, was tough to ID, but they both seem to be operating on my board. I've been able to see activity on both transmit sides of the optical link, but I haven't pulled the mainboard out (lots of screws and bits mounted to things), and I haven't been able to trace the receive path (I think I've found it on the analog RX side by shining a bright light and looking for the trace on the underside, but no guarantees). The mark near the digital side regulators on the silkscreen says the design is from 1990 and is numbered BLR-015631, perhaps the B00 firmware is only compatible with a different board revision. I don't have an error message saying that the Analog ROM is bad, and there is one mentioned in the manual, but I'm suspecting it because I haven't be able to ID an in between component acting bad, so I'm wondering if the ROM is damaged in a way that's just keeping it from responding. I've been checking all the connections I can between the two chips and haven't found the culprit yet, but I found that flashing the older B00 firmware to the replacement ROM chip just caused the relays to thrash on power up - very unhappy. ![]() I'm wondering if you could read and upload the C00 firmware for the analog ROM, or at least verify that the checksum is 0x00EB 98D8. Been trying to troubleshoot this Error 4 problem and have run into some interesting things. ![]()
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