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PotatoFi

This Does Not Compute SE/30

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One of my favorite YouTubers, This Does Not Compute, posted a video about reviving his Macintosh SE/30. I've watched a ton of his videos, especially regarding Game Boy front light, back light, and bivert mods. I don't know whether he's here on the forums or not. It's a good video, and I don't want to spoil it, so consider giving it a watch. Spoilers after the break.

 

 

Spoilers begin here!

Despite replacing the capacitors, he's still running into "Simasimac", or the strange pattern on the screen. He's no stranger to troubleshooting, but I do wonder if anyone here has some insight that could help him out. I mean, this is an SE/30, after all!

Edited by PotatoFi

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He should check the voltages at the floppy port (+5 & 12V).

If there is no chime then there might be a problem with the ROM. Clean and reseat the ROM.  Check connections of the ROM for continuity.

 

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Thanks for sharing my video!

 

I poked around the logic board a bit recently, and here's what I've found so far:

 

--All voltages present (+/- 5v, +/- 12v) at the 14-pin connector from the analog board.

--Continuity from the 14-pin connector to the edge connector for those voltage rails.

--All voltages present at the external floppy drive connector...except for -12v. Hmm.

 

Schematics show that cap C9 handles the -12v rail. It looks OK visually, but I might remove the new cap and take a closer look.

 

RAM and ROM SIMMs have had their contacts cleaned (both on the SIMMs themselves and their connectors). Haven't started checking the ROM SIMM slot for continuity yet.

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4 hours ago, ThisDoesNotCompute said:

All voltages present at the external floppy drive connector...except for -12v. Hmm. Schematics show that cap C9 handles the -12v rail. It looks OK visually, but I might remove the new cap and take a closer look.

Seems like a good lead. I can check my the floppy connectors on my Classic II and SE SuperDrive to see what the "working" behavior is like. I always check voltages at the floppy connector first, since it's easy to access and feels "safe" to probe around in. I'll be home to check that on Friday.

4 hours ago, ThisDoesNotCompute said:

RAM and ROM SIMMs have had their contacts cleaned (both on the SIMMs themselves and their connectors). Haven't started checking the ROM SIMM slot for continuity yet.

I wonder if swapping the ROM SIMM with a known working one would be a good test. There are also aftermarket solutions like the ROM-inator, but $42 feels like a bit much to spend on a shotgun part.

Edited by PotatoFi

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So the floppy voltage thing was a red herring. This page says -12v should be present on pin 5 of the external floppy connector:

https://allpinouts.org/pinouts/connectors/data_storage/macintosh-external-drive/

 

Turns out that's not true, at least for the SE/30. I found an original schematic for the SE/30 logic board, and it says pin 5 is simply not connected:

https://museo.freaknet.org/gallery/apple/stuff/mac/andreas.kann/SE30_SCSI1.GIF

 

I also measured the voltages present at the 14-pin connector. They're a little out, but not too horribly (and this is without a hard drive connected, so I'm not sure what kind of load the PSU was even seeing):

+5v: 4.8v

+12v: 11.65v

-5v: -5.1v

-12v: -11.8v

 

I'm starting to think it's a ROM issue, sadly. Any tips when trying to troubleshoot that?

 

EDIT: I think it's actually the +5v on the logic board. I'm getting 230 ohms between any +5v point on the board (pin 1 of the ROM SIMM slot, pin 120 of the expansion connector, etc) and the ground plane. I'm not getting any continuity between the other voltage rails and ground like that. So there's either some old electrolyte lurking somewhere shorting a +5v trace to ground, or my brand new cap at C11 is bad.

Edited by ThisDoesNotCompute

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The voltages are ok. The SE/30 should run with 4.8 and 11.65 V. The -12 V is not connected at the SE/30 floppy connector.

Perhaps you should clean the board with water and soap (and a soft toothbrush)  and IPA afterwards.

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The low impedance of the 5V bus is normal. Your measuring the effective load of all the chips including the PALs.

 

Do you have the pattern with no boot chime? if so your address/data bus is broken between the ROM and the system. So somewhere, you have an open trace. Guarenteed. I cant count how many of these boards I used to fix with various issues. 

 

What your going to have to do is grab the schematics, and start buzzing out ROM back to the rest of the system bus, to see where issues may reside. There is a break somewhere. 

 

If you get slow chimes instead of no sound at all, the ROM is booting but there is an issue with the system's ability to see and control the RAM. If this is the case, the 74F253 muxes could be the culprit here, or the traces near the first SIMM socket where that leaky cap resides. 

 

Sometimes traces broken at the ASC/SWIM/SCSI/SCC chip could mimic these symptoms. 

 

Edit: Just watched your video, As far as I can tell, the CPU cant see the ROM properly. there is a capacitor right next to the battery compartment that gets replaced, well its "goo" likes to break the address/data traces right there usually at the Via, or right at the ROM SIMM socket itself. So test each pin of the ROM socket back to the rest of the system on a matching point, that is where I would start if I were working on the board. 

Edited by techknight

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Yeah, after starting to go through the rest of the schematics I realized that all of the chips on the board use only +5v, and the rest of the rails are just passed through to other components (expansion slot, floppy drive, etc). And correct, there's no boot chime.

 

I tested all of the pins on the ROM SIMM slot to the muxes (D4 through D19, and UJ2/UI2/UJ3/UI3), continuity good there. I'll look closer at the C12 area, and after that, go back to the ROM muxes and keep testing forward from there. I'm also planning on giving the board a good soak in IPA, since all I've done so far for cleaning is just the surface.

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a good ultrasonic clean may help it, there could be conductive electrolyte stuck in the data bus somewhere. Its hard to say without seeing the board. You could even go as far as to wash the board in a dishwasher, dip it in IPA to displace the water, and bake it. I have had to do this numerous times with Mac Portable boards that had weird untraceable grimlins. 

 

Also when testing ROM connections, you need to go further back. you need to go back into the CPU area and pickup the connection testing from there. or even the PDS slot itself. 

 

the vias right next to the battery share the same tie points as the muxes, so the muxes can be broken along with the ROM SIMM socket, away from the PDS/CPU. I recall running into a few boards where I had to run patch wires from the ROM points back to the PDS. 

 

90% of the time though, I find the connections broken at the SCC/SCSI/ASC/SWIM area. But I havent found it to stop the booting process, unless the IRQ line from the SCSI IC is broken which will cause a floating condition. and can stop the machine from booting by holding a vector. 

Edited by techknight

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Yesterday I soaked the board in IPA for a few hours, then set it out to dry overnight. The problem persists.

 

I'm continuing to test the ROM connections. I've gotten through the muxes and resistor packs (RP4 through RP6) to their respective RAM slot pins, all are good. Next I'll work from the RAM to the glue chip I guess, and also check out the SCSI chip.

 

Hare are some photos of the board after cleaning: https://imgur.com/a/5r6or6s

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On 6/30/2019 at 12:53 PM, ThisDoesNotCompute said:

Yesterday I soaked the board in IPA for a few hours, then set it out to dry overnight. The problem persists.

 

I'm continuing to test the ROM connections. I've gotten through the muxes and resistor packs (RP4 through RP6) to their respective RAM slot pins, all are good. Next I'll work from the RAM to the glue chip I guess, and also check out the SCSI chip.

 

Hare are some photos of the board after cleaning: https://imgur.com/a/5r6or6s

Um sorry but I don't know If you have not covered this yet but, I have two suggestions. I have had many compaq macs end up having corrupted screens. If I were you I would look up ram configurations and manual test each ram card in the SE/30 and another mac that excepts the ram cards. To me that board looks fantastic and should not be to tough to get working. Another suggestion is checking the cable from the AB to MB board to check if the pins need to be metal polished. With any SE I've seen it has not been a problem but with Macintosh plus's its a common occurrence so I would just check incase that its that simple. I have not ever seen a macintosh SE need a big recap unless it was completely cooked due to over voltage but due to the air cooling fan and good parts even the worse one's I've seen could be fixed. If you acquire some big problem it like every one else says would be the ROM's but I rarely see that and again the Macintosh would probable looked like it had been cooked over an oven the board probably would have battery acid all over it and would be screwed. In summary I would check the obvious before going strait to hard stuff thats my advice it will save you alot of time and work.

BTW: when I mean clean the pins I mean the pins directly on the two boards and the connector I know you have already checked the voltages but its always good to see if your getting the best connection

Edited by Nathanplus

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If connections all check out, what are the chances of this just being a bad ROM SIMM? I wonder if we could procure a known-good one to send to you to test. I'd volunteer if I had an SE/30, but sadly I do not.

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41 minutes ago, PotatoFi said:

If connections all check out, what are the chances of this just being a bad ROM SIMM? I wonder if we could procure a known-good one to send to you to test. I'd volunteer if I had an SE/30, but sadly I do not.

I have a spare known good SE/30 ROM SIMM I would be happy to loan out if helpful.  If interested PM me @ThisDoesNotCompute

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Really quick I know this is an SE/30 but I was scrolling though Dead Mac Scrolls and one looked similar to The Programmer switch maybe being stuck. It sometimes also has out comes like this one.

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That ROM is on its way to you, hope it’s helpful! By the way since you brought it up, pretty sure a bad SCSI chip shouldn’t cause this - I had an SE/30 with bad continuity to a couple of the SCSI chip pins and it started just fine to a blinking question mark - just couldn’t see the hard drive. I was able to fix it (just added a jumper) with some advice from @techknight and others on here. 

Edited by Crutch

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As a bit of closure, and somewhat of a tease: I got my hands on another SE/30 board that suffered from a PRAM battery explosion. The board is toast, but there are still good parts on it. I swapped four of them over to my original board...and it works now. Expect a follow-up video in a few weeks. Thank you all for your help, I learned a ton!

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Holy freakin' cow @ThisDoesNotCompute, awesome video. That was worth the wait. Again, I don't want to spoil it, especially with the awesome build-up that you executed, so I'll refrain from talking about what fixed it here.

 

Here's a few of my notes which hopefully help out with the machine going forward.

 

Retrobrite: I did my SE FDHD in December, and if it has re-yellowed at all... it's barely, barely perceptible. I haven't seen the horror stories like you've shown in the video, and my Dreamcast and SNES that I did ages ago (referencing your videos, in fact) still look awesome. There's no brittleness. If/when you do retrobrite, I recommend full submersion in hydrogen peroxide + water like you did for your Gamecube back in the day. Be sure to pop the Apple logo out from the back, as the heat and hydrogen peroxide it can bleach out the red and yellow from the logo.

 

Here's the most recent retrobrite I did, on my Classic II.

 

Floppy Drive: If you don't intend to use the drive, this probably doesn't matter, but yours could use cleaning and lubrication. It looks like the eject motor is straining a bit, which can break the motor gear with extensive use. Taking it apart to clean and lubricate it is super easy. There's a video by What's Up TK Here, but it would be cool to see an updated video (hint hint). I use Dupont Teflon Silicon Lubricant for the sliding parts on mine. Not a ton of info here... but here's the last time I documented cleaning one of these drives. It's a bit messy because it's just a restoration log, not specific instructions.

 

Speaker: I don't have experience with the SE/30, but I'll bet your speaker failure is due to bad caps on the analog board.

 

I hope that helps, and thanks again for the fantastic video. Stoked that your SE/30 is up and running!

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Magnificent video!  Thank you so very much for your very detailed account of your thinking process throughout.  Great to see another one of these beasts up and running.

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