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Color Classic starts, but no chime / not booting from internal SCSI devices

Hello all!

I've got a set of head-scratching issues that I've spent days on but can't quite figure out, and was hoping someone here might have some thoughts. It's likely there's several different issues at play that I need to slowly work through. Apologies for the long read for those interested in helping!

I picked up a Color Classic recently that wouldn't turn on. It needed some work, namely a recap of the logic board. After the recapping it thankfully powered up, but didn't chime and wouldn't boot from the internal hard disk (flashing question mark). Okay, that's not unusual for 20 year old Quantum drives, it's probably a dead drive. I was then able to boot the machine up from my System 7 startup disks, and everything otherwise seemed fine (albeit slow, but that's a 16MHz 68030 for you.)

I was then able to verify that the audio hardware _is_ working overall by connecting external speakers during startup; the audio out is very quiet: my external speakers could barely register it at max volume, and a pair of headphones can make it out more clearly but still it's quiet.

So, ignoring the audio hardware for now, I installed a SCSI2SD I had in reserve. Start up via floppy, and it was able to see and initialize it just fine. But after installing System 7 _onto_ the SCSI2SD and restarting, it refuses to boot from it, bombing after the "Welcome to Macintosh" with a bus error (see screenshot). Restarting without extensions doesn't change anything; reinstalling System 7 again doesn't either. I've tried both System 7.1 and 7.5, same effect. Okay, perhaps I configured something wrong on the SCSI2SD. But after two days of messing around, I can't find anything that's wrong with the SCSI2SD, and was able to verify it works fine in my Quadra 700.

It was while checking the SD in my Q700 that I had the thought to try the original Quantum drive there, too. Sure enough, it boots up fine in the Q700. It's got System 7.1 on it. Putting it back in the classic and it's not even visible to Apple HD SC Setup. It's definitely getting power: I can hear it spinning up.

Now I'm starting to think perhaps there's something funky with the SCSI bus; The SCSI2SD _is_ recognized but won't boot correctly once it has a System Folder, and the Quantum drive isn't seen at all. Unfortunately I don't have an external SCSI device handy at the moment to test the ext SCSI port with (working on getting something cheap on eBay with which to test that).

I double-checked that all of the caps that I replaced on the logic board are seated well, going the right direction, and making good contact with their solder pads. I'm pretty green with a multimeter (I can check continuity on other things but my skills don't go much further than that) so I'm not quite sure what else to check out there.

My questions, I suppose:

- Is there anything obvious I'm missing with the hard disk(s)? Should I just wait to verify that SCSI is working at all by picking up something external, or is that maybe the wrong tree to bark up?
- Do y'all think the audio issues (internal speaker not working at all, speaker out being very low) is likely something on the analog board needing a recap (since it seems like at least the speaker routes up there for the front-panel controls), or something else entirely?

Thanks for any help you can provide!
 

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AwkwardPotato

Well-known member
Doesn't sound like you're missing anything obvious with the hard disk/SCSI2SD. It's possible that the sound and/or SCSI issues are a result of the analog board needing a recap, although serious trace rot in the audio section of these logic boards isn't unheard of either. Bear in mind that the analog board in the CC almost always needs to be recapped, just as a rule of thumb.

To rule out anything simple: on the bottom (solder-side) of the logic board, there are spring contacts that are meant to press against tabs on the RF shield underneath the board. Make sure none of the tabs on the shield are bent out of place, and that all of them make firm contact with the logic board contacts.

Also, with the hard disk installed internally, boot up the Mac and measure pin 25 of the external SCSI connector, with your meter in voltage mode, and with the negative probe on the shield/surround of the connector (you may need to put a thin piece of wire in pin 25 and probe that if the meter probe doesn't fit in the connector). You should be getting somewhere between +11-12V around +5V there (SCSI termination power) unless the power supply is weak/failing. If that voltage is low/not present I'd imagine it would cause instability.
 
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Thanks for the info!

Just ordered the caps I need for the analog board—I'll try recapping it when I get them.

I double-checked the logic board's spring contacts. They're definitely making contact with the RF shield.

The external SCSI connector has +4.84V on pin 25. That's a bit low, but maybe it's close enough?
 

crazyfrog

Active member
I have a similar issue. My color classic boots, chimes and goes to a grey screen with a bluescsi and premade images from this mega archive. I've tried both the 7.1 and 7.5.3 images and both lock at a grey screen, without an sd card the color classic gets to a floppy disk icon obviously meaning theres no disk inserted.
I've just done a recap of both the analog board with low esr caps as needed and tantalum caps on the logic board.
I've also tried the DIY db25 external bluescsi in the photo, no difference.IMG_3726.jpg
 

Tam 400

Well-known member
Have you checked your drive ID-0-1-2-3-4-5-6-7
0 is always start up.an if you have 2 drives with the
same I’d you will get a conflict On start up.I havnt
red this post fully,but I can see you have a boom
and no chime,no chime on start up is a hard ware
trubble for sure.SCSIC can be btch.from the pic
I can see your video is fine,just need to work out
the hard ware,hope I can help you out,cheers
 

crazyfrog

Active member
Have you checked your drive ID-0-1-2-3-4-5-6-7
0 is always start up.an if you have 2 drives with the
same I’d you will get a conflict On start up.I havnt
red this post fully,but I can see you have a boom
and no chime,no chime on start up is a hard ware
trubble for sure.SCSIC can be btch.from the pic
I can see your video is fine,just need to work out
the hard ware,hope I can help you out,cheers
No but you got me thinking about terminations so I soldered on the terminations I didn’t think we’re necessary on the bluescsi board. The documentation is really crap for bluescsi but I’m also really grateful for it.
 

AwkwardPotato

Well-known member
The external SCSI connector has +4.84V on pin 25. That's a bit low, but maybe it's close enough?
That ought to be good enough. The term power on these systems is usually supplied through a diode, which has a forward voltage drop of about 0.5V (actually implies that the +5V from the analog board is running a tad high at ~5.3V, although that's not high enough to cause problems). At any rate, the fact that you get 4.84V there confirms that neither the fuse nor the diode on the logic board for the SCSI ports are blown.
 

crazyfrog

Active member
On my old (non color) classic I removed the logic board caps with a iron rather than hot air so I could connect them to a component tester. Everyone I tried was absolutely shot, the reading were not even out of spec just a thousand times out or unreadable.
 
Update: I recapped the analog board last night. No changes, unfortunately: hard drive still isn't recognized and no audio from the built-in speaker. I'm honestly not sure what to try next.
 

crazyfrog

Active member
Update: I recapped the analog board last night. No changes, unfortunately: hard drive still isn't recognized and no audio from the built-in speaker. I'm honestly not sure what to try next.
The hard drives die. Bluescsi f4(yes get the f4 version) is a great and cheap solution that you can even DIY or order pre built.


i know there are issues with the Apple 343S0045-B chips failing but some enthusiasts are making progress here
 
One thing I noticed while recapping the analog board: this resistor looks rather suspect. But I've no idea if it's crucial to anything important.
 

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AwkwardPotato

Well-known member
That resistor and the two diodes near it run extremely hot even under normal use and tend to darken like that. If it fails it'll manifest itself as display problems.

How bad was the cap leakage before you cleaned the motherboard? If it was in rough shape you may need to start inspecting the traces around the CPU and audio IC for corrosion/breaks. As far as SCSI issues go, there's also a non-zero chance that the SCSI IC is bad (from a previous owner plugging the wrong kind of device into the external port, for instance). Unfortunately the SCSI controller on these is combined with the SCC into the 85C80 IC, and the only source for a new one would be a donor motherboard.

The DFAC audio IC could also be bad, but given how you were able to hear very faint audio, it's more likely a rotten trace due to cap leakage (possibly under the chip). The schematics for this board are floating around online, you may want to verify every single connection in the audio circuit. On the off-chance that chip is bad, you'd again need a donor board (or if you have enough will-power, hack in a few op-amps to replace the sound output half of the chip, since it only functions as a filter).
 

3lectr1cPPC

Well-known member
Unfortunately the SCSI controller on these is combined with the SCC into the 85C80 IC, and the only source for a new one would be a donor motherboard.
The good news would be that so many throw aside the CC boards for 575 upgrades that finding a donor board shouldn’t be too difficult.
 
That resistor and the two diodes near it run extremely hot even under normal use and tend to darken like that. If it fails it'll manifest itself as display problems.

How bad was the cap leakage before you cleaned the motherboard? If it was in rough shape you may need to start inspecting the traces around the CPU and audio IC for corrosion/breaks. As far as SCSI issues go, there's also a non-zero chance that the SCSI IC is bad (from a previous owner plugging the wrong kind of device into the external port, for instance). Unfortunately the SCSI controller on these is combined with the SCC into the 85C80 IC, and the only source for a new one would be a donor motherboard.

The DFAC audio IC could also be bad, but given how you were able to hear very faint audio, it's more likely a rotten trace due to cap leakage (possibly under the chip). The schematics for this board are floating around online, you may want to verify every single connection in the audio circuit. On the off-chance that chip is bad, you'd again need a donor board (or if you have enough will-power, hack in a few op-amps to replace the sound output half of the chip, since it only functions as a filter).
Thankfully cap leaking wasn't _terrible_. There was visible wet spots around each cap, but none of the traces or chip legs had obvious corrosion. I'll take some time to inspect closer with a magnifying glass, track down those schematics, and test the legs on the audio chip and maybe the SCSI controller chip. I'm thinking you're right, at this point it's likely something on the motherboard I've missed.

Worst case, yeah, hopefully the "fix" could also be replacing the logic board with a CC board that I can get on the cheap or just eventually finding an LC 575 board for a reasonable price if I'm lucky. I've seen them come up on our local Craigslist once or twice over the past few years for "not-eBay" prices, I just hadn't had a CC to put one in at that point.
 
Another update: I read through the schematics for the CC logic board (I'm really not good at doing so, but I managed. 😅). One call out I noticed is that two capacitors (C2 and C3) are part of it. So, I decided to first try removing and re-soldering both caps again (I also did the caps C4 and C5 just in case).

Sure enough, started up and chimed. So clearly one of the caps wasn't making full contact with one of its pads.

I'm wondering if something similar might be happening with the SCSI bus so I'm going to do another look over off all the caps and the schematics and see what might be there.
 
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