Harmful to run SE/30 temporarily without recapping?

[djc6]

I have an SE/30 whose logic board is in decent shape - considering its age. The Original battery was still intact (and now in the trash) so just some electrolyte corrosion.

My question, is it really harmful to run it without replacing capacitors? Capacitor C5 had come off completely.

Why would I want to run it this way? I was to do some troubleshooting to see what chip(s) are causing lack of vertical sync. So I can order the caps and other parts at the same time to save on shipping. I suspect one of the SOIC chips in the video circuitry, their legs are corroded. I wanted to run the machine long enough to probe around with my oscilloscope to hunt down the bad IC. I get a happy mac chime via the headphone jack, so the CPU is executing code and I believe this means the RAM is OK?

I am bench testing the logic board with a CayMac Vintage SE/30 Compact Analog & PSU Replacement Board and a PicoPSU. So I am not using the original power supply or analog board.

 

[Nixontheknight]

I have an SE/30 whose logic board is in decent shape - considering its age. The Original battery was still intact (and now in the trash) so just some electrolyte corrosion.

My question, is it really harmful to run it without replacing capacitors? Capacitor C5 had come off completely.

Why would I want to run it this way? I was to do some troubleshooting to see what chip(s) are causing lack of vertical sync. So I can order the caps and other parts at the same time to save on shipping. I suspect one of the SOIC chips in the video circuitry, their legs are corroded. I wanted to run the machine long enough to probe around with my oscilloscope to hunt down the bad IC. I get a happy mac chime via the headphone jack, so the CPU is executing code and I believe this means the RAM is OK?

I am bench testing the logic board with a CayMac Vintage SE/30 Compact Analog & PSU Replacement Board and a PicoPSU. So I am not using the original power supply or analog board.

if a capacitor came off, DO NOT RUN IT, get it recapped as soon as possible

 

[François]

I don’t think it’s really harmful to run it, C5 is part of the audio circuitry, so you just won’t have sound. The problem is not the missing capacitor, but the leaked electrolyte from failing capacitors that is eating, and thus destroying, the circuit board. So better remove the remaining electrolytic capacitors, and thoroughly clean the board, checking for potential damage, before replacing the caps.

I think we all have run computers with failing capacitors! I sure have run my SE/30 in such a state: when the sound coming from the internal speaker is at a very low volume, even at the maximum setting, is when you know that the capacitors have failed and need to be replaced.

 

[djc6]

I don’t think it’s really harmful to run it, C5 is part of the audio circuitry, so you just won’t have sound.

Thats how I felt, but I see many DO NOT RUN posts when I searched here and other forums, without reasoning why. I thought if C5 was missing the circuit is open and power is not getting to whatever would be powered. I thought the capacitors on the logic board were to smooth out voltages, and I'm not using the original power supply but instead a modern PicoPSU while bench testing.

The problem is not the missing capacitor, but the leaked electrolyte from failing capacitors that is eating, and thus destroying, the circuit board. So better remove the remaining electrolytic capacitors, and thoroughly clean the board, checking for potential damage, before replacing the caps.

I did this on another SE/30 and it worked out well. This is my second SE/30 restoration. I'm still looking for good ideas for cleaning up corrosion around these SOIC package chip legs in the video circuitry. One my other restoration a little vinegar worked well - kept it on the board only for five minutes or so and only in the affected areas. Any other ideas or is vinegar a safe bet?

 

[François]

In case you didn’t know about it already, the schematics for the SE/30 logic board have been redrawn using modern software! Get them on github. They may be useful for troubleshooting…

 

[phipli]

Thats how I felt, but I see many DO NOT RUN posts when I searched here and other forums, without reasoning why. I thought if C5 was missing the circuit is open and power is not getting to whatever would be powered. I thought the capacitors on the logic board were to smooth out voltages, and I'm not using the original power supply but instead a modern PicoPSU while bench testing.

You shouldn't run a circuit that has leaked electrolyte on the board.

The reason is that the electrolyte allows electrolysis to happen - it strips the outer surface off pins and things corrode way faster than when a computer is just sat on a shelf. The damage tends to concentrate on the power pins, so much so that you can tell which pins are the power pins. Running a machine with no visible damage, but that the caps have leaked, then putting it back into storage for a few months gets you this :

 

[phipli]

I dug out the original photo, so here it is in higher resolution :