Hi Guys, my ambitious repair project isn't progressing, so I wanted to ask for some hints:
Got a sick SA that doesn't seem to boot:
I have left it in the loading screen for 20 minutes, nothing changes.
Found an interesting serial interface, but it too gets stuck without putting out anything useful (to me at least):
Both previous owner and I tried swapping RAM chips with NOS parts, but that changed nothing or made it worse:
![](https://i.imgur.com/faCzDcW.jpg)
Changing the red marked Toshiba TC551001CF for what looked like brand new ones, caused complete deadness, not even self test was executed.
All the EPILDA Chips are new, solder joints were inspected with a microscope and look good. RAM self test passes too, but that could be testing the main processors RAM?
The Main processor is a Motorola MC68340, the flash card contains some interesting verbose files and some binaries:
https://drive.google.com/file/d/1XZMoc3Zd86UlXWMjUhN6VH5KTtQ_qpTr/view?usp=sharingBut nothing in there has helped me so far.
I have changed some parts in the switching power supply and now I am very confident that it intact.
![](https://i.imgur.com/NkfBv6M.jpg)
J12 was my serial interface, unpopulated J20 has some continuous high frequency digital signal going on, doesn't look like something meant to be read by human. J10 is silent permanently.
I have looked at the board with a thermal camera and found nothing suspicious.
I have unplugged everything (Coax connectors, floppy drive, front panel, all the RF boards, rear interface board) and that only caused more errors in the self test and the instrument didn't proceed to the loading screen any more.
I have temporarily replaced the backup battery, which fixed the appropriate self test fail, but didn't make the initial problem go away.
The previous owner has a working one of these and might be coaxed into making a measurement, if that helps me.
Apart from that the only option I see now is play around with the chips around the large Advantest labelled devices.
I wouldn't be surprised if the initial self test is only performed by and on devices around the Motorola processor in the top right corner.
As soon as it sends the boot message via serial it might hand over to the Advantest devices which may keep their errors to themselves.
In particular I could remove individual RAM chips and see if that changes anything visibly. If not, then that chip might be broken without a visible sign.
Thank you for reading, hope we can solve this puzzle, so that more interesting HF stuff can happen
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)