Folks, I thought we could use the LC520 motherboard inside an LC575 computer body, but apparently not. My LC520 board is now dead!
Some of you may recall my LC520 recapping video, and my 84V VGA Mod video. As you could see, I had a working LC520 board even prior to the recap, and it worked fine after recap, and I could use it on my Color Classic with the 84V Mod installed, along side the stock CC motherboard and LC575 motherboard.
In the past, my LC575 computer worked fine with the LC575 motherboard it came with, and you can see it powered in my Mystic Upgrade video. I purchased that LC575 on the cheap here in Japan for the lone purpose of extracting its motherboard, especially because the plastics were cracked, chipped, and ready to fall apart. Later, I desoldered one of the audio amplifier chips from the LC575's Analog Board in order to solder it into my Color Classic's Analog board for the Stereo Mod.
I kept the LC575 body in storage since the stereo mod. But this past week, I decided to get rid of the LC575 body, but before that I wanted to use it to check some things like the content of the spinner drive it came with. Not wanting to risk harming my precious overclocked LC575 motherboard, I decided to use my LC520 motherboard in the 575 body, because I had the understanding it was OK to do that. Sadly, it seems to have killed my LC520 motherboard.
I did the following this week, in the order listed below:
- I properly removed the Analog Board in order to reinstall the two Audio Amplifier Chips. (I had two spare chips taken from an LC520 Analog Board that I later junked. And yes, I soldered them into the LC575 Analog Board correctly. I cleaned off the flux with alcohol and gave it 24 hours to fully dry before testing.)
- I reinstalled the Analog Board properly.
- I installed my LC520 motherboard properly, and yes, the bottom metal prongs make ground contact with the metal frame of the computer.
- I connected my ADB IIgs Keyboard and ADB Mouse to the LC520 motherboard inside the 575 body.
- I connected the power cable, then flipped the back side switch to ON. I could hear that the CRT circuit was powered with the normal "boom" sound. It's a bit louder and bolder than the Color Classic's sound, but perfectly normal for the 575 due to its larger CRT.
- I then pressed the power key. Nothing. No bong. No CRT display. No LED lit on front. No HDD spinning. No case back fan spun. No sign of life at all !!!!
- I measured at the LC520 motherboards connectors to see what voltages I could read:
(a) Meter GND to SCSI pin-7 (GND) and Meter POS to SCSI pin 25 (Term. PWR). No voltage when I flipped ON the PWR SW, and nothing when I pressed the PWR key.!
(b) Meter GND to top left pin of ADB connector, and Meter POS to top right pin of ADB. At PWR ON, voltage slowly rose to 106mV, but it should be 5V! - I removed the case back from the LC575, flipped the PWR SW ON, and used my thermal meter. Various components get hot, which is what I would expect.
- I powered OFF, removed the LC520 motherboard, then put the LC520 board into my Color Classic (with 84V mod). I flipped ON PWR, heard the CRT power-up boom sound, then pressed the PWR key on my IIgs keyboard. No bong. 100% black CRT. My heart sank! But I do hear the case fan and see the machine is powered.
- I removed the LC520 motherboard and installed the LC575 motherboard into the Color Classic. It bonged and booted up perfectly.
- I am not seeing any visible signs of burn marks on my LC520 motherboard. No smoke, nor any bad smells on it either.
QUESTIONS:
- Is it really WRONG to use an LC520 motherboard inside an LC575 body? Or have some of you done that successfully? If you have successfully done it, then it means something else inside the 575 computer body must have killed my LC520 motherboard.
- Any ideas what might be dead on my LC520 motherboard? Identifying that would potentially lead to a fix.
Thanks.
