Mac SE/30 SCSI problem

[TjLaZer]

OK my spare SE/30 is having a major problem! I think it's the SCSI chip. Which is not socketted!

It will hang on boots and reboot, and after messing with it, SCSI is dead on the machine. Cannot read or boot from a HD. It will boot up fine from floppies. right now its automatically rebooting once it loads the Finder from disk. Tried resetting the PRAM. I removed and looked over the MB, and reseated all SIMMs. No go. Looks like its done.

 

[phreakout]

TjJazer,

Try rebooting the SE/30 off of the floppy drive. Then run Disk First Aid or Apple SC HD Setup or some type of equivalent hard drive utility program. We just need to check if whether in fact it is the SCSI bus that is the problem or whether it is just a hard drive issue. If you can see the hard drive in the utility program but not mount it on the desktop, then it is the hard drive that is the problem, not the SCSI bus.

Are you able to boot off an external SCSI storage device plugged into the back of the SE/30? If you can, then I would say you may just have a bad Bourns network filter, located at RP2 on the logic board. Remove that and the internal SCSI should fire right up; although, obviously, when you remove the Bourns chip you disable use of external SCSI connector.

Give this a try and report back with results.

73s de Phreakout. :rambo:

 

[TjLaZer]

Turned out to be leaky caps! Cleaned it up and it works. But I snapped one cap off so I ordered a set of caps to replace 'em all.

 

[phreakout]

Do you need someone to replace the caps or are you comfortable doing the job yourself? Send me a private message if you need assistance.

73s de Phreakout. :rambo:

 

[zuiko21]

Hi all,

After washing and recapping my SE/30´s mobo, it now starts with a loud, clear "bong" -- no more SimasiMac! Here it is, connected via LocalTalk to my Quadra 700 (as AppleShare server):



It is productive, as you can see More pics (and video!) of the restoration at the flickr set.

...but still won´t boot from the (known good) SCSI disk -- either external or internal, although it boots fine from a floppy. I´m thinking of a bad 53C80, which I could fix -- have the spare and, hopefully with the help of the Electronics Department of my School, the ability to replace it ;-)

Anyway, I observed the following:

-Upon startup, it doesn´t lock at the checkboad pattern -- after a few seconds, the floopy icon with blinkng ´?´ appears as expected.

-Every time it does a SCSI bus scan, the activity LED of any connected device (external or internal) does make a brief flash, seems like "being polled"

-If "improper" termination is used, the scan takes much longer (6-7 sec)

-Tried any termination/connection scheme, even swapping cables.

-Checked with a DMM the resistance of the lines in RP3 and RP10 -- without desoldering them. All lines measure 50 ohm, as expected.

-HD SC Setup sees nothing in the bus.

However, here comes the weird part: SCSI Probe 4.3 does see "something" in the bus... it says ´no data´ on the line for each device present -- with correct SCSI IDs.

Does anyone here think of any further testing before declaring the 53C80 as the culprit?

Thanks a lot in advance,

Posting this from my Quadra 700 (68 MiB) + 7.6.1 + Netscape 4.0.4 ;-)

 

[trag]

I would very carefully examine the area around the 53C80 chip for damage/corrosion from the leaking capacitors. Also, to the extent you can, visually trace the connections to the 53C80 pins back to their origins and then check them with an ohmmeter to confirm that there's actually a good connection there.

In other words check continuity from each 53C80 pin to the pin of whatever other component it connects to. Make sure the circuit board is still doing its job. This will be tedious.

The output side of the 53C80 should be fairly straightforward, as the pins should connect to the appropriate pins on the SCSI connector.

Do you have a datasheet for the 53C80? That has the pinout and will give you a better idea of what each pin should connect to.

Cast an especially critical eye on any circuit board vias which connect traces to the 53C80. On my IIci (back in the 90s!) capacitor leakage pooled in a via and corroded the copper lining such that the traces on front and back of the circuit board were no longer connected. The damage was not really visible until I used magnfication and even then it took a continuity test to confirm.

If there's a schematic of the SE/30 logic board available get that and use it to check the 53C80 connections. Failing that, the block diagram in "The Guide to the Macintosh Family Hardware" would be helpful. Looking at the block diagram for the IIci (developer note available as PDF) it looks like the peripherals sit right on the main data and address busses.

Ah, forgot about this. I have the 53C80 datasheet available here: http://www.io.com/~trag/DataSheet/Z53C80.pdf. The D7-D0 lines probably connect pretty directly to the CPU data bus. The address lines and the other control lines may pass through one of the two VIA chips. The IRQ line almost has to.

Still, doing a comparison of the 68030 pinout and the 53C80 you should be able to line up a good number of the pins to check.

 

[zuiko21]

Hi Trag, many thanks for your reply.

I would very carefully examine the area around the 53C80 chip for damage/corrosion from the leaking capacitors.

This makes a lot of sense... I remember seeing some greenish stuff on the 53C80's pins



(hmm... I think that pin is Vdd)

In other words check continuity from each 53C80 pin to the pin of whatever other component it connects to.

Yes, it seems the easier way to do it. Thanks for the advice.

The output side of the 53C80 should be fairly straightforward, as the pins should connect to the appropriate pins on the SCSI connector.

Will be the first to be checked... After further experimentation (with some abnormally excessive termination), SCSI Probe was able to sort-of-read the name of one of the disks on the chain. It said UUENTUM LT646W instead of QUANTUM LP240S -- that's the DB2 bit gone crazy!

But I'll eventually check every 53C80 pin. Should any connection show up as defective, I'll begin the (tedious) work of visually inspecting the board in search of the flaw...

If there's a schematic of the SE/30 logic board available get that and use it to check the 53C80 connections

Fortunately I have one! I can't remember the source anyway, I'll check later.

Ah, forgot about this. I have the 53C80 datasheet available here: http://www.io.com/~trag/DataSheet/Z53C80.pdf.

Thank you very much!

The D7-D0 lines probably connect pretty directly to the CPU data bus. The address lines and the other control lines may pass through one of the two VIA chips.

It's a surprinsing scheme... data lines come from the CPU bus, of course, but are actually D24-D31 (!). Address lines come from the bus also, but they're A4-A6. Both sub-buses are easily checked at the comfortable, large DIL pins of the Video ROM. Of the remaining lines, many are exclusively connected to the Glue chip.

The IRQ line almost has to.

Certainly -- VIA2's CB2 input.

Again, thank you very much for your help -- you're the real saviour of my SE/30! ;D

I'll be back with the results of the checkout. Cheers,

 

[zuiko21]

It's been a while, but here's some news: it's not the SCSI chip, but one broken connection!

 

[pbMacGeek17]

zuiko21,

Which connection was broken? The problem you encountered is VERY similar to what I'm trying to resolve on my newly recapped SE/30 (my system reports that the SCSI Bus is not terminated). Any receommendations regarding where on the MOBO you found the bad connection would be much appreciated.

 

[zuiko21]

Hi!

It's the DB2 line, between pin 39 on the 53C80 chip (the uppermost pin on the right side) and pin 6 on the IDC-50 internal SCSI connector. It's also connected to pin 22 on the DB-25 external SCSI port, but there's perfect contact between both SCSI connectors -- I had put with my bare fingers a jumper between the chip's pin and the corresponding line of the IDC connector, and the SE/30 was able to read and boot from a CD on the external port!

I've been very busy these weeks, but I'll try as soon as possible to reflow (with my recently acquired hot air station) the SCSI chip, in case it's just a bad solder problem...

 

[trag]

The link to the 53C80 datasheet has changed from to http://www.prismnet.com/~trag/DataSheet/Z53C80.pdf

Basically, anywhere I ever used io.com, it is now prismnet.com. I wish I could do a global search and replace across the internet...

 

[pbMacGeek17]

Gents, thanks for the quick update. Just got done watching about 4 of TheTechKnight's Youtube videos on resolving SE/30 problems to see if I could learn more. He also had a SCSi problem and traced it

to a similar cause (bad connection, not bad chip). This gives me hope that my board can be fixed without having to replace the chip (bigger task than I care to take on). I downloaded the Z53C80 doc

(thanks, Trag) and assume the pinouts are the same as for the NCR 53C80, but don't have a schematic for the board. Consequently, it's still difficult to verify the connections. Anyone know where I can find a copy of the SE/30 schematic? SCSIProbe is reporting that the SCSI bus is not terminated so I believe my problem is not identical to either zuiko21's or TheTechKnigts, but I think it's likely just a different connection that's broken.

 

[BGoins12]

That was my board in the video. It would boot up to the question mark, but wouldn't recognize any SCSI devices whatsoever. He fixed the bad connection and it works great now.

 

[pbMacGeek17]

Cool. The symptoms were very similar to my problem, but on your board, the software at least detected that something was out there. On mine, SCSIProbe just blinks "SCSI Bus Not Terminated" and only shows the Mac itself at SCSI 0. I'm convinced it's nearly an identical failure, but also just as convinced it's a different pin (1 of 42). Guessing which pin clearly won't get me there, hence my search for documentation. I'm going to check the termination pin on the 53C80 first. I've got to check Trag's refernce to see if it states what the voltage for that pin should be. I'm limited to a simple multimeter/continuity tester for testing so anything that requires a scope is out of my league.

 

[pbMacGeek17]

ixnay on the ematicschay request. I just realized that zuiko21 gave me the logic board connections for the 53C80 in the link in his response. I thought it was a pix of his board and I hadn't gotten around to looking at it until just now. The drawing may be a little cryptic to interpret, but I'm up to the challenge. Thanks zuiko21!!

 

[techknight]

check to make sure you have termpower at the DB25 connector as well. if not, theres the issue.

 

[pbMacGeek17]

techknight, thanks for weighing in. Your videos were very helpful in getting me rolling, but I'm afraid I'm lacking background information to act on your current suggestion. What I have is a drawing of the 53C80 with connections to various pins on the internal and exernal connectors. What I don't see is which pin would be termpower, nor what voltage I should be looking for (assuming +5V). Can you provide some clarification?

 

[pbMacGeek17]

techknight, If i did my research correctly, I should have seen +5V across pins 24 and 25 of the external DB25 connector if the SCSI bus were working correctly. Unfortunately, I measure no voltage differential between 24 and 25. So, if that's the problem, what's the cause? Is this a hard drive failure or something else and how do I diagnose the problem? The hard drive is configured for SCSI ID 0 with all terminating resistors installed. I appreciate any insight you can provide.

 

[trag]

Z53C80 and NCR53C80 are the same part from different manufacturers. Often, one manufacturer will license the part from another. In some cases, they develop the part independently, but with the same functionality and pinout. In those latter cases, one should compare the datasheets, because sometimes there are subtle differences which turn out to matter.

In this particular case, The Z means that Zilog made the chip. NCR means that National Cash Register (before they's chip division mutated into SYMBIOS*) made the chip.

*Later, SYMBIOS or part of its library was bought by LSI Logic, so ultimately, what started as a NCR53C96 (related, later SCSI chip) finished its production life as an LSI53C96.