Netronics Elf II repair

[Old Computers]

I recently acquired a Netronics Elf II in non-working condition. Due to a lot of poor solder joints I have started to remove each piece and clean the rosin from the traces and components. I am almost to the point where I will start working with the IC chips. Should I just leave the chips alone to prevent damage, or should I re-solder them? If I re-solder them I plan on buying sockets for each chip. Another reason why I would want to re-solder the chips is to perform the tests the manual describes before having the chips installed. What do you guys think?

In addition to poor solder joints I believe that a missing jumper may be causing the power supply to not be connected to the remainder of the circuit.

Old Computers

(If this is in the wrong section I can delete this and move it.)

 

[Old Computers]

I went ahead and left the IC's alone except for some really bad solder joints. The computer partially warms up. The voltage check specified in the manual checks out okay. The display lights up, and displays 00. When I press 88 to perform the manual's checks the display shows EF. Then it becomes un-responsive. Two of the chips run very warm, which I think may have something to do with the problem. What do you guys think?

Update: When I turned the computer on the displays were rapidly changing (the run switch was on). I think that is a good sign that the CPU is running.

 

[Old Computers]

Another update. When I did some more testing today, the displays were flickering when the computer was turned on with the load switch turned on and run switch off. Turning off the load switch stopped the display from flickering. I do not know what that would mean. I checked a resistor (R27, 47kOhms) that I thought might be out of tolerance. It read 0 ohms. I am going to remove it from the circuit to do a better test. The strange thing about this resistor is that I cannot find it in the schematics. I believe it to be a part of the control switch circuit (not the hex keypad circuit), but it could also have something to do with the keypad. I found the data sheets for the two chips that run hot. I will check the waveforms and voltages that the datasheets for the chips specify.

The suspect chips are 74c173 and 74c922

 

[Old Computers]

I found that R27 is not supposed to be installed. I read the manual and moved it to its proper location, R26. The more I think about it the more I believe that the two chips are the problem. When I operate the run, memory protect, and load switches, I get responses from the display that seem to coorespond with the proper operations.