Rooster wrote:I just repaired my ASR-10 with blank screen and self test characters on the display. The problem was a bad capacitor inside the keyboard assy on the "coil board". It's laborious because you got to remove all the boards from the ASR and then remove the keyboard assy and then remove all 61 keys just to get to the plastic mount that holds the 2 coil boards. I found schematics for the coil board but had to be careful because the schematics are not accurate. The capacitor was right on the threshold of working. When it heats up it "pops" on. It's part of the "power on reset" for the keyboard processor. And of course when I desoldered the capacitor it stunk pretty bad. For those tech savvy guys out there The capacitor is a 3.3 microfarad surface mount cap. It is tied to pin 6 of IC part number 7555 (It's a standard 555 timer IC) U9 is the location designation. The schematic is not accurate and does not show the cap in the circuit. But I know enough about 555 timers to know and see "no reset signal" coming out the chip. I had data coming in from the digital board to the Ensoniq 5702000102 chip U2 pin 27, but no data out from pin 26 to the digital board. That's when I noticed no power on reset. The cap was just bad enough to hold keep the timer from resetting. I didn't have a 3.3 microfarad cap so I used a 2.7microfarad. Actually, it worked without a cap installed. This cap value just provides "reset delay time". Anyway its fixed.
Hey Rooster I'm aving the same Problem. Changed the 7555. All caps around the 7555 are OK but I'm also getting nothing out of the pin 26 like you had
Voltage on pin 27 is there. Do you have any idea?