exxos's Atari, Amiga & retro forum

Probably the thing to do is go around all the blitter pins with a scope and see if anything looks odd (the address bus will look like total crap anyway). Though there isn't much else it can be other than a bad solder somewhere. You should also check with a meter all the blitter pins you can which go back to the CPU & GLUE.

Do you have access to a diag cart at all? I have one that runs the hardware tests and includes a blitter test which might get error codes relating to the problem.

One thing I have seen on these chips and their bretheren (Glue, MMU), is that it is possible for the pins to get twisted and to touch their neighbor on the chip, so it's worth flipping the blitter over on it's back and having a quick check.

It's also well worth checking that the pins are all clean (Socket and blitter), and in the case of the socket, are extended enough to make contact when in the socket.

Also, there is variance between sockets (I think exxos reported this) in that he divider between pins on the socket varied and caused problems with contact, so worth plugging in the chip and using a magnifying glass to check the socket isn't causing problems.

Yeah there was a whole thread on PLCC sockets...

https://www.exxosforum.co.uk/forum/viewt ... ?f=23&t=74


Generally 3M seem to be only good ones so far.

exxos wrote: 30 Jul 2019 16:11 Yeah there was a whole thread on PLCC sockets...

https://www.exxosforum.co.uk/forum/viewt ... ?f=23&t=74


Generally 3M seem to be only good ones so far.

Ahh, that's the topic I was looking for!

Thank you both I really appreciate it - This is very frustrating !

exxos wrote: 30 Jul 2019 12:50 Probably the thing to do is go around all the blitter pins with a scope and see if anything looks odd (the address bus will look like total crap anyway). Though there isn't much else it can be other than a bad solder somewhere. You should also check with a meter all the blitter pins you can which go back to the CPU & GLUE.

I started this job today, as far as I can tell soldering of the socket seems good, there's no shorts between pins either.
Is there a (legible) schematic that includes the blitter anywhere to be found do you know? would be useful for this.

rubber_jonnie wrote: 30 Jul 2019 12:58 Do you have access to a diag cart at all? I have one that runs the hardware tests and includes a blitter test which might get error codes relating to the problem.

One thing I have seen on these chips and their bretheren (Glue, MMU), is that it is possible for the pins to get twisted and to touch their neighbor on the chip, so it's worth flipping the blitter over on it's back and having a quick check.

It's also well worth checking that the pins are all clean (Socket and blitter), and in the case of the socket, are extended enough to make contact when in the socket.

Also, there is variance between sockets (I think exxos reported this) in that he divider between pins on the socket varied and caused problems with contact, so worth plugging in the chip and using a magnifying glass to check the socket isn't causing problems.

Alas I do not, and the blitter is nice and clean with no bent pins on the underside.
What I did do is attach a pin to the multimeter and test continuity between the top of each IC leg and the edge of the PLCC socket. Most were good , but some seems to need a little fettling before I got a beep. Could tie in with the evil PLCC socket theory.

Ill have another go at soldering the IC direct to the board. Another thing I've noticed is that the PCB is actually slightly warped in this area. Probably a manufactuing issue but its making my job a little harder.

Or Ill order a 3m socket and see if thats any better.

Thanks!!

Cimmerian wrote: 30 Jul 2019 17:33 Is there a (legible) schematic that includes the blitter anywhere to be found do you know? would be useful for this.

The 520ST schematic Is the best quality, but it does not include the blitter. But maybe you can use the remake schematic as its basically the same as the STF anyway.

exxos wrote: 30 Jul 2019 17:38 The 520ST schematic Is the best quality, but it does not include the blitter. But maybe you can use the remake schematic as its basically the same as the STF anyway.

wow thanks - nice work :)

exxos wrote: 30 Jul 2019 17:38 The 520ST schematic Is the best quality, but it does not include the blitter. But maybe you can use the remake schematic as its basically the same as the STF anyway.

My Blitter now works! :yay2:
Thanks Exxos - that Schematic turned up something interesting:
(

Excuse the state of the pads here Ive had this thing on and off more times than a....
You may notice Pad 22 - it disintegrated when soldering it early on - luckily its not used. :?
Also I'm afraid Exxos' pacman sticker has not survived multiple blasts of hot air ...
)

Anyway Pin 29 is meant to go to BGACK on the CPU . You can see close to pin 29 what looks like a via actually doesn't go anywhere for some reason on this rev. board, it doesn't even go through to the other side. I noticed this earlier, but payed it no mind until I started using the schematic testing continuity signal to signal, unfortunately after I decided to ditch the PLCC socket and try soldering direct to the board again.

Added a bodge wire as so:
and everything now works.
I'd be interested to understand why this is so, could it be they never really expected anyone to ever install a Blitter onto this Rev. ? Or perhaps service technicians had instruction to add this trace in should they ever have had to fit one.

Oh wow well done!

I will have a look tomorrow to see if I have the same revision board. I guess its possible the PCB on that revision is wrong.. But nobody has found that issue yet.. I'm sure people have fitted the blitter to that style board before, so maybe its one particular revision.., we need to look into that ...

:bravo:

This is a C103175 REV.1 It has the track and I checked back to the CPU...I sucked the holes to show where its going..

Can you post the bottom side of your board ?