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KnobsNSwitches

LC 575 board (in Color Classic) - funky vertical lines

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I took a chance on an unknown condition LC 575 logic board for upgrading my Color Classic. 

The good news: it boots! The bad news: it looks like this: 

 

 

(don't mind the error message on the screen. I haven't moved over the right system enabler for the 575 board in the color classic yet. I just wanted to test booting yet)

I don't see any obvious capacitor goo on the board, but I did give it a rinse in distilled water and a scrub with a toothbrush and the screen still looks like that. Any ideas of what could be causing the picture?

IMG_5701.JPG

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22 minutes ago, beachycove said:

Reseat the 575 vram simm, or try another.

There are 2 installed (I need to verify if they need to be in pairs), I have reseated and swapped their locations. I don't have any spares, I'll need to seek some out.

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A few years ago, I had one bad vram simm in a 575 logic board (installed in a CC too) that caused very similar anomalies. It’s possible that vram could explain your troubles. The nice thing in this case is that all vram is easily replaceable, as there is none soldered onboard. The bad thing is that you need additional vram Simms to test the possible fault.

 

You have no other machine from which to borrow some?

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6 minutes ago, beachycove said:

You are relying on the ResEdit hack, right?

Yes. 

 

7 minutes ago, beachycove said:

A few years ago, I had one bad vram simm in a 575 logic board (installed in a CC too) that caused very similar anomalies. It’s possible that vram could explain your troubles. The nice thing in this case is that all vram is easily replaceable, as there is none soldered onboard. The bad thing is that you need additional vram Simms to test the possible fault.

 

You have no other machine from which to borrow some?

Sadly, no, the CC is my only vintage desktop. I have some 30 pin SIMMs and several PowerBooks, but nothing else to borrow some from.

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The resedit hack is all about the screen, so make sure that's done right before going further. I somehow missed the enabler reference in the original post, so maybe be sure the software is right first. 

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Just an update to this thread.

I purchased some new VRAM from memoryx.com, but the symptoms persist. 

(I should note, the lines are visible on screen before booting goes anywhere, on the happy mac, 'welcome to macintosh' etc. )

 

I recapped the board, just in case, if nothing else to practice my soldering, but still have the same issue. I must keep digging. 

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I've a similar issue with my LC575 board, is the Mac "usable" and does it boot to desktop?  If so, still VRAM but could be a bad trace on the connectors themselves.  I've not recapped mine yet.

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On 3/30/2018 at 9:10 AM, KnobsNSwitches said:

I took a chance on an unknown condition LC 575 logic board for upgrading my Color Classic. 

The good news: it boots! The bad news: it looks like this: 

 

 

(don't mind the error message on the screen. I haven't moved over the right system enabler for the 575 board in the color classic yet. I just wanted to test booting yet)

I don't see any obvious capacitor goo on the board, but I did give it a rinse in distilled water and a scrub with a toothbrush and the screen still looks like that. Any ideas of what could be causing the picture?

IMG_5701.JPG
 

 

That is hot!! I do not know why..but I start picturing Apple // when I saw this picture.

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On 5/16/2018 at 12:43 AM, Byrd said:

I've a similar issue with my LC575 board, is the Mac "usable" and does it boot to desktop?  If so, still VRAM but could be a bad trace on the connectors themselves.  I've not recapped mine yet.

I missed this response somehow. Yes, it is "usable" in that it does boot, but it's really hard to see any thing. ;-)

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The board arrived at my place and I think I found the culprit already:

 

IMG_5048.thumb.JPG.10e2395bf7cf5f5a0d93788acdd0057a.JPG

 

That's the RAMDAC. I quickly popped it off but everything looks fine underneath:

 

IMG_5052.thumb.JPG.690bc39759f043f98fbfef447cc6404d.JPG

 

Also gave the chip a quick treatment, doesn't look too bad anymore:

 

IMG_5053.thumb.JPG.d7b4a32610f0565cdfd6241990a95434.JPG

 

At least it still has all its legs connected and not rotten off yet.

Let's hope it was just a failed connection outside of the IC and it did not start rotting on the inside. I will put it on again in the next days and see if it resoldering it already fixed the issue.

If not I am going to try to carefully cut it open a little bit and see if the internal traces to the die are also corroded.

 

Also took a quick look at possible donor machines... LC475, Quadra 605 and 610 (and maybe all the other Quadras as well) do share the same RAMDAC in case I need a replacement IC.

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Was not going to say it as harsh as you did, as he said he used it as a board to practice soldering on.

My first attempts have been worse I would say :p

 

 

As a side note to @KnobsNSwitches: you used quite a lot of solder, you don't need that much with surface mount parts. Also be sure to heat up not only the pads but also the "legs" on the component itself as well to make the solder bond with them as well. I like to apply some solder to one of the two pads, heat that solder up and keep it hot while putting on the cap. As soon as solder bonds to the cap remove the heat and simply solder on the other side.

That way you will also be able to solder the components down all the way and not have them sit on a tiny hill of solder.

Edited by Bolle

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Quote

Was not going to say it as harsh as you did

Didn't want to be rude.

 

Yes, not enough heat on both sides.

 

I try to use a minimum of solder on the each pad of the capacitor, this will keep the cap as flat as possible, heat one side until it will bond to the board, then i do the other side and use some more solder and heat on both sides.

 

This will get solid and shiny welds.

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Bolle, glad the board finally made it out of customs and am impressed you're getting to work on it right away. I appreciate the updates and the soldering tips.

 

bibilit, yes, this was indeed my first soldering job. Thank you for clarifying, I thought you were being just being rude.

 

I'm getting better but looking at my latest board the caps still aren't flat. I need a better way hold the cap down while heating one side at the time. Practice will make perfect, I guess.

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  • Quote

    I need a better way hold the cap down while heating one side at the time
     

    I use tweezers for that purpose.
     

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I just tin both pads, use tweezers to hold it in place while I solder one side, and then use my finger to push it into the solder on the other side as I heat it, and then reflow the other side.  Just be quick so you don't burn your finger!

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Put the RAMDAC back in place, the corrosion cleaned up nicely:

 

IMG_5071.thumb.JPG.edbe99fbab4d4f7acd1bb2bd2a027569.JPG

 

I was still getting the same artefacts as before so either the chip was bad or there was something else wrong.

I took out my working 575 board to check a few things. I started figuring out the pinout of the VRAM SIMMs to have a starting point for tracing things backwards. Then traced all connections going to and coming from the RAMDAC.

The LC475 dev note says that video data is shifted to the VRAM from the main data bus (D0-15 to SIMM 1, D16-D31 to SIMM 2). Addressing is done by the memory controller which has 9 separate video address lines. /RAS, /CAS, /WE and the clock signal for the serial output ports of the VRAM ICs are coming from the memory controller as well.

Video data is fetched by the RAMDAC through the serial outputs from the VRAM.

With all that info put together in a messy spreadsheet I started going through all the connections on the broken board.

 

Video address line 1 seemed to not make it from the memory controller to the SIMM sockets. All address lines traced fine to the resistor packs (acting as filters) on the back of the board, however from there VA1 did not make it's way to the sockets.

It was not a broken trace though but a faulty solder joint. I don't see how that could have happened. There was no solder on there at all. This must have been a factory error, unless someone already put their hands on the backside of that board:

 

IMG_5074.thumb.JPG.220df7357d3e4a8fada0768284fc90f9.JPG

 

Soldered that little guy down and resoldered all the other resistor packs as well for good measure.

The result was a better, but still not completely good picture:

 

340887810_dataline.thumb.jpg.a8f424ae5f08993f859619e23917d20e.jpg

 

The lines started to fade away and come back while the machine was running, so there must have been intermittent contact somewhere or a trace with higher than normal capacity.

I went through all the serial data lines between VRAM and the RAMDAC twice. On the first time everything checked out just fine but on the second go there was one data line (luckily) not giving any continuity.

If it would not have decided to stop working right when I went for a second check I would have been looking for the problem forever... not sure if I would have done a third turn going through the same signals.

It looks like the trace connecting to the solder pad was causing the issue. I put in a short patch from the pad to the next via and got a steady beep from my multimeter now ;)

 

IMG_5082.thumb.JPG.7ee1f99fecc308ce686f934e63a13f75.JPG

 

And the result:

 

IMG_5085.thumb.JPG.017f39836e285cb1b14167baa8575378.JPG

 

 

 

Now that was fun :D

 

Edited by Bolle

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Finally. Someone out there thats as good as I am at this stuff. 

 

So now I can finally retire on repair to focus solely on my day job as it is an ever growing time sucking black hole.

 

Been wanting to for awhile but found it hard. 

Edited by techknight

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As always, @Bolle, most excellent work.  Very well done!

 

@techknight, no.  not allowed.  [;)]  But seriously, I for one can definitely understand the time sink.  Get wrapped up so far in work and repairs, then there's no time to to actually play.  Although, there is a certain degree of satisfaction when something clicks and it finally works.  Thanks so much for the years of contributions on here, and your youtube videos.  And I hope your retirement is sporadic at best.  [}:)]

 

 

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