| Electronics > Repair |
| HP 3314A Function Generator--No Display |
| (1/1) |
| N2IXK:
Have a 3314A on the bench that I am trying to bring back to life. Powers up, fan runs, but none of the displays or annunciators light up. Not even a brief blink at startup. A quick check of the power supply rails found +/15V OK, +5V was around 1.6V. The 470 uF output filter cap (C105) on the +5V rail was found to be open (read 8 nF). Replacing it restored the +5V, so now the power supply is apparently functioning OK. All 3 rails at proper voltages and free from ripple. Because of the 1 bad electrolytic, I will plan to completely replace all the electrolytics in the unit. The lithium CMOS battery was also stone dead, and beginning to leak. Clipped it out. But restoring the power supply rail has failed to bring back any display or other sign of operation. A few quick checks with a scope show that the 2 1MHz clocks are running OK, and probing random pins of the CPU and memory shows bus activity. The LED on the controller board comes on at power up, blinks a couple times as I hear a few reed relays somewhere clicking, then then goes out. It would seem the the CPU is booting and executing code, at least up to a point. Tack soldered in a 3V coin cell in place of the dead CMOS battery, no difference. The power supply rails are making it to the front panel/display board. No chips seem to be getting excessively hot on any of the boards. This is apparently a later production unit (1987/1988 date codes on most parts, with only 2 ROMS on it, rather than 6.) The 2 ROMS (U206 and 207) look like they have been replaced, as the sockets appear to have been soldered in by hand, and the chips (27256 EPROMS) do not have HP labels/part numbers on them, just handwritten ones saying U206 and U207. The service manual troubleshooting charts and the various self tests you can initiate using the DIP switch all presume that you have a signature analyzer available, which I do not. Does anyone have any suggestions how to proceed from here? Any place I can get the files for the ROMs, so I can compare to what is on mine? Only seem to find the files for the 6 chip mask ROM version of the board. Thanks, and appreciate the input... |
| wn1fju:
Go to K6JCA site: https://k6jca.blogspot.com/ Select the two posts concerning HP3314A. Lots of repair ideas there. Also links to the ROM images on KO4BB's site. |
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