4mb memory upgrade guidance

[ShawnT62]

[I have installed the 4mb upgrade on my 520st (rev 70243).

No I am stuck. I have attached a picture of the screen I get when powering on, just garbled. I do think this is a good sign and I have just done something stupid (wouldn't be the first time). I have checked my wiring, have continuity on 4 wires between mother board and expansion, I have continuity from solder points on expansion to underside of motherboard. Not sure where to go next. Have attached some images but more can be supplied if needed.

Thanks

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[exxos]

Is that wire on the MMU shorting out on pins next to it ?

[rubber_jonnie]

Is that wire on the MMU shorting out on pins next to it ?

My thought was the same as yours. I'd check for shorts to the other nearby pins.

[ShawnT62]

Nope, it is not shorted (does seem like a crap solder job which I will fix but not shorted.

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When I was taking that shot, I did notice this, the pins for the four wires are resting on the cap below, is this a problem I should fix or will it be ok?

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[exxos]

It shouldn't be a problem...

I'd suggest you grab then ST shamatic and continuity check all the RAM lines from the motherboard to the upgrade board.

You can put one probe on the motherboard and gently run the other probe down both sides of the dram chips and make sure you get connections.

That MMU wire, if you have something like a 1k resistor you can tie it to 5v somewhere and it will only allow 1MB but may help rule out problems with that wire...

I don't think anything looks wrong with the install. But it's easy to damage pads and tracks etc...

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[ShawnT62]

sorry for stupid question but could you say that differently.

For example if I were to use R135, 136,137 as base point, where should I get continuity at the hi/low points of the expansion. WhatI mean by Hi/low is how they are mounted, not sure if its pin2/9 or 1/15. Also from the 16 points, where should I be checking for continuity or making sure there isnt.

Sorry, electronics as a whole isnt my strong suit, I follow instructions but when they dont work, I get lost.

I am concerned about the pads on the mother board as I had a few stubborn pins that solder sucker wouldnt get when taking ram out and had to resort to iron and manual sucker and was a little agressive with heat :( that is on me but that was why I checked the continuity now each pin.

[rubber_jonnie]

OK, so don't take this as being criticism, take it a a learning point.

Your desoldered areas are very untidy, and one especially:

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It looks like either pin 1 and pin 16 or pin 8 and 9 have been solder bridged. It's difficult to tell as the pic is a bit fuzzy, but I would check continuity between those two to start with as they shouldn't be connected.

After that I would get some solder wick and clean all the unused holes to make sure there are no bridges or excess solder in the area you've been working.

Then I would start on the left hand side underneath and follow the traces and make sure there is continuity for the entire length of each trace. You'll see the traces that you need to follow.

You should also continuity check the pins to be sure they are connected top to bottom, so from the pin on the memory expansion to the other end at the bottom of the mainboard.

Again, not a criticism, but lots of problems like this are down to soldering issues. Bridges, damaged tracks and pads etc. I can't stress enough that taking the time to do a clean job is half the battle.

[HigashiJun]

Who knows if a trace is not broken...

The area around the via is really dark, like burnt.

[ShawnT62]

Thank you for feedback. I will go back and see what I can clean up,

I know i am poor at soldering skills, and try and do better on each project. I will clean up and test again.

[rubber_jonnie]

Thank you for feedback. I will go back and see what I can clean up,

I know i am poor at soldering skills, and try and do better on each project. I will clean up and test again.

Again, not being critical here, just some advice.

If you are aware enough to say your soldering skills are poor, then practice on something you don't care about before jumping into something tricky like an ST upgrade.

ST mainboards are old and easily damaged in that pads can be pulled off the board, vias damaged, and even internal failures caused by manual handling of the boards.

We all started somewhere and I've done all of the above plus some other stuff too, but the key here is practise, and do it on something that you don't care about, such as a soldering practise kit.

I know it seems sensible advice in hindsight, but that's just the way it goes. You're not the first and I doubt you'll be the last :)

Let us know how you get on.