Freshly Recapped Portable - RAM Faults

[Garrett]

I’ve been sitting on one too many Portables needing a recap. Yesterday I decided to get moving and actually complete one. Apart from these boards sucking a TON of heat from my iron, the job was straightforward.

Keep in mind I did not test this board before the recap as to not cause damage to the sensitive Hybrid board. When it came time to power up, I found my power supply and connected the leads directly to the battery terminals. Booted right up, but oh no- death chimes!



00000003
00000010

According to “Troubleshooting Your Macintosh” it looks like a major error of 03, indicating a RAM fault. Minor error is 10, which I assume is RAM data bit 4?

I broke out the multimeter and tested for continuity between pin 16 of each RAM chip, which should correspond to RAM data 4, and found no breaks. Looks like one or more chips may be defective. The traces I can see look fine. Obviously I haven’t removed any chips yet to look under for breaks.

Seems like the only real option I have is to start replacing chips one by one (after I find replacements of course). It’s not a total loss though- the LCD is in great shape, and the speaker is nice and loud!

 

[SuperSVGA]

If you're feeling adventurous and have the means to hook up a serial cable and ground pin 7 on J22, you can likely get into the test mode and possibly isolate the bad RAM there, assuming there isn't an issue with data bit 4 across all of the RAM.

 

[Garrett]

If you're feeling adventurous and have the means to hook up a serial cable and ground pin 7 on J22, you can likely get into the test mode and possibly isolate the bad RAM there, assuming there isn't an issue with data bit 4 across all of the RAM.

I may have heard about this, serial diagnostic mode? The only documented info I could find is here:

Diagnostic Mode - mac68k - Confluence

web.archive.org

I have an SE/30 with working serial ports, and a bit of patience (ha). Would be fun to give this a go. What kind of client would I need on the SE/30 to send and receive commands to/from the Portable?

 

[SuperSVGA]

I have an SE/30 with working serial ports, and a bit of patience (ha). Would be fun to give this a go. What kind of client would I need on the SE/30 to send and receive commands to/from the Portable?

Anything like MacTerminal or Red Ryder probably should work fine. Proper settings should be 9600 baud, 8 bits, 2 stop bits.

Be warned that linked documentation is missing most of the commands and has some commands that aren't in the Portable ROM.

For example to run a march test on the first 256KB (no spaces or newlines):

*S
*A
*4
*0 00000000
*1 0003FFFF
*T 000600010000
*R

 

[Garrett]

I had a bit of time last night and decided to try the serial diagnostics. Here’s my setup- it’s crude but worked just fine!




On the other end was my PowerBook 1400 running OS 8.6 and ZTerm software. I tried MacTerminal but it wasn’t playing nice.

Immediately on power up, I started receiving the following line every second or so. Identifier code of 6 designates the Portable.



Upon trying the test suggested by @SuperSVGA I ended up with this error. Looks similar to the one I saw initially with the Sad Mac?



Out of curiosity, I tried a ROM test and got this back. Looks normal to me?



Now my question is, what do the characters after the *0 and *1 signify? I understand S stops the repeating message, A and 4 define what form of input I’m entering, T is the definition of the test itself, and R is result output.

Are there any other RAM tests I could try? This will be really neat if it works!

 

[SuperSVGA]

Now my question is, what do the characters after the *0 and *1 signify?

*0 loads the starting memory address and *1 the end.

If you try testing RAM on two different ranges, for example 00000000-0003FFFF and 00040000-0007FFFF, and you get the same error in both, then either bit 4 is bad on multiple chips or there is an issue with bit 4 across all of the RAM.

 

[Garrett]

*0 loads the starting memory address and *1 the end.

If you try testing RAM on two different ranges, for example 00000000-0003FFFF and 00040000-0007FFFF, and you get the same error in both, then either bit 4 is bad on multiple chips or there is an issue with bit 4 across all of the RAM.

I’ll admit I don’t quite know why the portable needs 32 chips to comprise a total of 1MB. Would be be similar to four sticks of 8 chip 256k RAM in an SE? I wish I knew the logic of what was going on.

Either way, I was able to perform additional testing. It appears the error is isolated to RAM data bit 4. I ran multiple tests, in 1 bit increments, starting from 0. As this was tedious to type in, I created a text file that I could send to the Portable. Pretty slick!

Results are below. As was mentioned, the only test to error is 00030000-0004FFFF. Bits above and below are good.

I do have some replacement chips on order, but the question now is, how do I know which chips correspond to what? They aren’t labeled on the board.

 

[SuperSVGA]

As was mentioned, the only test to error is 00030000-0004FFFF. Bits above and below are good.

I do have some replacement chips on order, but the question now is, how do I know which chips correspond to what? They aren’t labeled on the board.

Assuming the select lines are connected in order, that range would match 4 chips, but since the error is in the lower byte the two chips for that range should be U4B and U1C.

 

[Garrett]

Exciting update! My replacement chips came and I started with U1C. Little flux and hot air - came right off. Unfortunately no change, same sad Mac code. From there I moved onto U4B. Success! I was greeted with a flashing floppy disk.

I then added the RAM card that came with the portable (turned out to be 3MB) and ran Snooper. Passed two cycles of RAM tests just fine. So exciting. Yes yes, my test setup is even sketchier than before.

Big thanks to @SuperSVGA for the help in identifying faulty chips.

While I was at it, I swapped out the crusty trackball rollers with some new ones I found on eBay. It’s so much smoother now.

Up next is a new hybrid to solve some quirkiness with power ups and charging.

 

[Paolo B]

Could you please share the link to the rollers spare set? I was planning to tackle that issue on my own, by casting or turning something, but if the solution is already out there it makes no sense…
Thanks!

 

[Garrett]

Could you please share the link to the rollers spare set? I was planning to tackle that issue on my own, by casting or turning something, but if the solution is already out there it makes no sense…
Thanks!

The item number is 335176346660 from seller “DasherDeals”. I thought the price point was too good for me to try my hand at making my own. Time is money!

 

[chrisrueckert]

Congrats to finding and fixing the issue. I get a similar error, though it's 0000FF00 in the second row. Which RAM chip could that be?

 

[Garrett]

Congrats to finding and fixing the issue. I get a similar error, though it's 0000FF00 in the second row. Which RAM chip could that be?View attachment 14729

I’m not sure what the FF00 exactly is, but I agree that the 3 is a RAM fault. The minor code is marked by the FFxx as seen below, except this guide shows nothing for the 00 you’re seeing… I wish I was more help!

 

[SuperSVGA]

I get a similar error, though it's 0000FF00 in the second row. Which RAM chip could that be?

The test has marked the upper byte (bits 8-15) of RAM as bad, so it could be any of the chips in the lower half.
While it could be a combination of bits on multiple chips (for example 3 bad bits on one chip and 5 bad bits on another), it's more likely one or more chips are bad or failing to select.
To narrow it down without replacing all the chips on the upper byte you would likely have to use the serial connection to test individual sections of RAM.

 

[techknight]

I didnt know about the diagnostic modes, Loving that. However its very cryptic, i wonder if a tool could be made to run those commands for you and then spit out which chip is bad.

 

[SuperSVGA]

I didnt know about the diagnostic modes, Loving that. However its very cryptic, i wonder if a tool could be made to run those commands for you and then spit out which chip is bad.

A simple program/interface could probably written, and then run on basically anything with serial hardware. I suppose you could even do it from a smartphone.

You can actually do quite a lot from that interface. Besides running the various hardware tests, you can dump memory, execute code, and even send commands to the power manager (turn power to hardware on and off, read voltage, read/write PRAM, etc.).

 

[techknight]

A simple program/interface could probably written, and then run on basically anything with serial hardware. I suppose you could even do it from a smartphone.

You can actually do quite a lot from that interface. Besides running the various hardware tests, you can dump memory, execute code, and even send commands to the power manager (turn power to hardware on and off, read voltage, read/write PRAM, etc.).

Ahh, its probably how the TechStep communicates with these machiens then.

 

[Sideburn]

Wow. I have a shelved portable board that I had fixed traces, swapped out the hybrid with SuperSVGA’s (though it wasn’t the issue and I killed a perfectly good OEM hybrid ), and re-capped and it too had the same type RAM error. I combed over the entire board and located all suspicious/ broken traces and continuity checked every RAM chip and then had to shelve it since I could’nt figure out which chip or bank it could be on. this serial port diagnostics idea is great.

I have the same error code but the second lines FF are at the far right end location:

 

[chrisrueckert]

I had a bit of time last night and decided to try the serial diagnostics. Here’s my setup- it’s crude but worked just fine!


View attachment 14530

Where did you connect to the PA

Where and how did you connect Ground and PA0 (Pin 2 of the VIA)? I‘m trying to get the diagnostics mode working and am stuck at this point.

Also, did you take a standard serial cable to connect the two Macs? I have one that works fine for a Mac-to-Mac LocalTalk connection and will take that one.

 

[Garrett]

Where and how did you connect Ground and PA0 (Pin 2 of the VIA)? I‘m trying to get the diagnostics mode working and am stuck at this point.

Also, did you take a standard serial cable to connect the two Macs? I have one that works fine for a Mac-to-Mac LocalTalk connection and will take that one.

Pin 7 must be grounded on the edge connector. I used a paper clip as a little jumper. All you need to do is make contact.

Yes, a standard Apple serial cable will work fine!