Hi I recently just purchased an original macintosh 128k logic board as the one in my 128k was upgraded 512k. When I turn it on it just comes up with the sad mac error 040800 does anyone know if this is something to do with the ram if so what is the best replacement for them
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Macintosh 128k sad mac error code 040800
- Thread starter Macintosh68000
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Check solder joints on yoke connector (especially bottom-most pin of the 4) Most likely under a double-sided tape square).
Check the soldering of pin 5 of the main power/video connector (centre of the analog board - this is the cable that goes to the logic board).
I take it this was working fine before the FBT swap ?
Check the soldering of pin 5 of the main power/video connector (centre of the analog board - this is the cable that goes to the logic board).
I take it this was working fine before the FBT swap ?
yes it did not have any issues with displaying picture before the FBT swap the only issue it had was the FBT was shorting and causing the computer to reboot that's the reason it was replaced in the first place. But either way I will try them connectors and let you know how it goes.
Ok I just worked out the issue is with the logic board as I was using the 512k board to test the analogue board as I did not want to risk damaging the 128k board. But anyway I put a mac plus logic board in there and it worked fine and I put the original board back in and it displayed the sad mac icon so the issue was in the 512k board and not the power supply. So what could be the issue with this 512k logic board now.
would this be a good Ram chip replacement for the 128k https://www.ebay.com.au/itm/64K-x-1...837988?hash=item3439d93e64:g:AcgAAOSwSw5d2gCS
https://www.ebay.com.au/itm/TMM4125...m2d08f3dfcc:g:ErwAAOSwIh1elnUr&frcectupt=true or would this be a better one
just replacing as many components on that 512k logic board till I find the issue with the thin line
I replaced the caps and a few transistors on the board one of the transistors was shorting at the pins but still the same outcome. Are there any known parts on the logic board that can cause the horizontal line.
It is very rare for logic board faults other than RAM on 128 512 & Plus.
The chip involved in generating Hsync & Vsync is the "LAG" 16r8 logic IC (at location 1E)
Though not impossible, I'd be looking at other intermittent problems first (dirty/burnt/tarnished resulting in poor connectivity of Pin 5 of the video/power cable - ie the green wire).
The chip involved in generating Hsync & Vsync is the "LAG" 16r8 logic IC (at location 1E)
Though not impossible, I'd be looking at other intermittent problems first (dirty/burnt/tarnished resulting in poor connectivity of Pin 5 of the video/power cable - ie the green wire).
Thanks for you're help replacing the ram chip fixed the issue with the 128k logic board. But there is a bit of an audio issue when I am playing games on it like stunt copter for example every 5 seconds it makes a tick noise. And it also reboots after 20 to 30mins of being used I replaced the optoisolator as that can be a common cause for them issues but it still makes that tick noise but hasn't rebooted on me as of yet.
Periodic ticking sounds like a High Tension discharge or arcing. I can't say I've seen it on the 128 Analog board, but it CAN be a sign of insulation breakdown INSIDE the flyback transformer's windings 
You might want to check that the Flyback transformer isn't dusty, dirty or cracked. Clean the FBT body and resolder it's pins.
Check the earth point (black wire with white stripe) at the top left CRT mounting ear (viewed from behind) and the short green earth wire (near the mains power socket) is screwed to the metal chassis.
Check that the folded metal piece is in place at the bottom rear of the analog board. It fits over the edge of the analog board and contacts the chassis on one side and the copper traces on the circuit board and two screws are used to fix the board to the chassis there.
You might want to check that the Flyback transformer isn't dusty, dirty or cracked. Clean the FBT body and resolder it's pins.
Check the earth point (black wire with white stripe) at the top left CRT mounting ear (viewed from behind) and the short green earth wire (near the mains power socket) is screwed to the metal chassis.
Check that the folded metal piece is in place at the bottom rear of the analog board. It fits over the edge of the analog board and contacts the chassis on one side and the copper traces on the circuit board and two screws are used to fix the board to the chassis there.
Sorry for the late reply just been very busy the past month I replaced the optoisolator with another one and it turned out the first one I replace it with was a dud so the resetting issue is fixed. And the ticking noise doesn't do it with any other game besides stunt copter and I'm assuming it's due to the fact the game runs much slower with 128k making it noticeable when the audio track reloops.