Hi - I am a new M102 owner, but have a collection of other TRS-80s (M1 & M4). I recently acquired this M102 on eBay, and as disclosed it has a "black screen" on startup. The following is what I have done so far, none of which has changed the situation. I would appreciate any and all additional guidance.
1. Cleaned up evidence of corrosion (battery compartment, and possible old leakage from a cap or two in the PSU section). 2. Replaced the visibly suspect capacitors in the power supply section of the motherboard. 3. Replaced D13 with an HRP22 equivalent (a 1N5819, although it's silicon rather than glass -- not sure if this makes a difference). I checked the diodes as best I could with my multimeter, and noticed that D13 had a forward voltage of greater than 0.6v (it was double or more) and also showed voltage in the other direction too -- which to me indicates it's shorted and so I decide to change it. The new one tests the same way, so perhaps it's an in-circuit test anomaly or something else? Regardless, all voltages on the board appear to be in spec (see note #9 below). 4. Removed, cleaned and reinstalled the AA battery carrier as I noticed some corrosion and expected some had leaked below the carrier itself. 5. Replaced the RAM backup battery with a new NiCad battery. 6. Cleaned all contacts and connectors for the LCD and keyboard, and checked the cable for continuity. 7. Removed all the 24K of RAM, installed sockets and replaced it with new RAM. I have tested with one 8K RAM (in the standard RAM slot #1/M9) using both old and new chips with no change. 8. Checked and validated all VDD, VEE, VB voltages are in spec. when the unit is on (w/backup battery on), and when unit is off (w/battery back up on), and with ALL off. 9. Confirmed there is 5v on CPU, ROM and all RAM chips and their sockets. I do not have an oscilloscope, but I do have a logic probe, more than happy to dive in to solve this with some guidance. Stay safe, and thanks in advance. Alan
