Macintosh LC won't mount external SCSI drives

[geokov]

Hello,
I have a problem with my Macintosh LC that I can't seem to solve. I runs well except it won't mount any external SCSI drives. I have tried three different SCSI drives that I have and a CD drive. The LC sees them but they won't mount. When I use SCSIProbe, it sees the drive but its info is gibberish. When I try Snooper, it see the drive but says it can't read the drive type. I get the same result with each drive and it doesn't matter which SCSI ID I use for them. The internal SCSI main hard drive functions well with no issues. I have experimented with an external BlueSCSI v2 Pico but that hasn't worked either so far. Currently running 7.0.1.
Any help would be greatly appreciated.

 

[LeadedSolder]

How's the continuity from your SCSI controller IC to the port itself? I had a lot of trace damage around mine on my LC I from a big electrolytic cap stuck to the top of the controller leaking.

 

[Elemenoh]

How is the internal drive jumpered? I recently had a LCIII that wasn't mounting external SCSI devices of any sort. I noticed the internal drive (a transplant fro, something else) was set to ID1. I changed it to ID0 and external stuff started to work.

 

[geokov]

How's the continuity from your SCSI controller IC to the port itself? I had a lot of trace damage around mine on my LC I from a big electrolytic cap stuck to the top of the controller leaking.

Hi, thanks for taking the time to reply. Luckily my LC didn't have that large capacitor over the chip although I have seen photos of LC boards that do have it. I just downloaded the schematics so I can start checking the continuity to the controller. I have some hope because it sees the drives, it just won't mount them.

 

[geokov]

How is the internal drive jumpered? I recently had a LCIII that wasn't mounting external SCSI devices of any sort. I noticed the internal drive (a transplant fro, something else) was set to ID1. I changed it to ID0 and external stuff started to work.

Thanks for taking the time to help, I'll have a look for that.

 

[geokov]

How's the continuity from your SCSI controller IC to the port itself? I had a lot of trace damage around mine on my LC I from a big electrolytic cap stuck to the top of the controller leaking.

I printed out the SCSI schematics for my LC and tested everything. I did find that there is a problem, I have marked it on the attached schematic. I can't see anything obvious with my naked eye, the continuity from the internal SCSI to the chip is good so that narrows it down to something with pin 11 (DB5) on the port itself or with the trace from the port to pin 12 on the internal SCSI connector.

 

[geokov]

How is the internal drive jumpered? I recently had a LCIII that wasn't mounting external SCSI devices of any sort. I noticed the internal drive (a transplant fro, something else) was set to ID1. I changed it to ID0 and external stuff started to work.

I tried changing the ID to 0. Unfortunately, it didn't have an effect on the problem.

 

[LeadedSolder]

I printed out the SCSI schematics for my LC and tested everything. I did find that there is a problem, I have marked it on the attached schematic. I can't see anything obvious with my naked eye, the continuity from the internal SCSI to the chip is good so that narrows it down to something with pin 11 (DB5) on the port itself or with the trace from the port to pin 12 on the internal SCSI connector.

From the name, I think this is one of the data lines, so it makes sense that you're just getting mangled garbage back from the hard drive when you query for ID strings. But then how is the internal SCSI drive still working?

Edit: Sorry, I misread the initial post. The trace is broken to the external port but not the internal port, which makes sense. See if you can visually follow the trace with magnification to the perimeter of the port – I bet it's a bad via or maybe even a cracked solder joint on the SCSI port, if DB5 is physically on one of the outside pins. You could try scraping back the solder mask on the trace and doing a "binary search" probe to see if you can figure out where the break is.

Are you probing the pin on the port, or the pin soldered into the logic board? Might be some corrosion on the port itself.

If you can't find the break after some more searching, I would consider just running a jumper wire from the SCSI controller right to that pin, which at least would confirm the cause.

 

[geokov]

From the name, I think this is one of the data lines, so it makes sense that you're just getting mangled garbage back from the hard drive when you query for ID strings. But then how is the internal SCSI drive still working?

Edit: Sorry, I misread the initial post. The trace is broken to the external port but not the internal port, which makes sense. See if you can visually follow the trace with magnification to the perimeter of the port – I bet it's a bad via or maybe even a cracked solder joint on the SCSI port, if DB5 is physically on one of the outside pins.

Are you probing the pin on the port, or the pin soldered into the logic board? Might be some corrosion on the port itself.

I probed both the pin on the port and where it is soldered at the back of the board. I can't see any breaks in the trace but there is a pretty sketchy looking via. I'm going to try re-soldering the pin in question on the port first, if that doesn't change things then I'll move on to the via and then to looking for a break in the trace.

 

[LeadedSolder]

Yeah, that should be fine. LC SCSI is super slow so it's not like you have to worry too much about matching trace lengths or anything... I suspect plugging the via will take care of things. Good luck!

 

[geokov]

Yeah, that should be fine. LC SCSI is super slow so it's not like you have to worry too much about matching trace lengths or anything... I suspect plugging the via will take care of things. Good luck!

Thanks for all your help, I really appreciate it. The one in the circle is the trace and via in question but they all look a little crunchy in that area, I need to clean them up. If you don't mind one last question, what do use for the initial cleaning of corrosion like this? Before any soldering.

 

[LeadedSolder]

Yeah those vias under the "L" in "L3" look corroded!

Personally, I usually use an Olfa knife to scrape off the solder mask, but I know others use a fibreglass pencil. It's never done anything for me but make itchy dust, but it might be a technique thing. After that you'll want to clear the via, which can be tricky. I have a small very pointy tip for my Hakko that clears out corroded vias pretty well, then I lay up some magnet wire across the trace on the top, through the hole, and onto the trace on the bottom. Then I plug the hole itself with solder and check continuity.

 

[geokov]

Yeah those vias under the "L" in "L3" look corroded!

Personally, I usually use an Olfa knife to scrape off the solder mask, but I know others use a fibreglass pencil. It's never done anything for me but make itchy dust, but it might be a technique thing. After that you'll want to clear the via, which can be tricky. I have a small very pointy tip for my Hakko that clears out corroded vias pretty well, then I lay up some magnet wire across the trace on the top, through the hole, and onto the trace on the bottom. Then I plug the hole itself with solder and check continuity.

Thank you. I had to do a repair elsewhere on the board where a capacitor exploded so I have some appropriate magnet wire. Clearing the vias could be a challenge, I have seen other people drill them out if they are particularly stubborn. I'll keep my fingers crossed. I got this cheap LC just to view some old SCSI drives we had in storage and of course the external SCSI port is the one thing that doesn't work.

 

[LeadedSolder]

A pin vise drill bit is also a decent option if you have one, though it's annoying to line it up and clean the wrecked copper around it sometimes. I have done that technique before as well.

 

[YMK]

If you don't mind one last question, what do use for the initial cleaning of corrosion like this? Before any soldering.

I reflow with new solder and flux. The flux carries the corrosion away.

 

[geokov]

I reflow with new solder and flux. The flux carries the corrosion away.

Hi, thanks for taking the time to help, that's exactly what I'm going to try.