Unhappy Macintosh 128k, Thick vertical lines

[gubbish]

Hi everyone,

I recently got a few compact macs from a craigslist seller - 2 128's, an SE and a Plus.

Tried them all out - SE is fine, Plus is not working (though I'll address that one later), and one of the 128s seems to be in working order, asking for a boot disk.

The other 128, unfortunately, is not so happy.

Turn it on, no startup bong sound, and the screen shows thick vertical lines. There are also some sprinkled pixels on the right side of the screen, and a few flashing pixels scattered through the rest of the display. No sad mac code visible.

This is an older 128, with just "Macintosh" on the back badge instead of "Macintosh 128k"

I have a copy of Pina's "Macintosh Repair&Upgrade Secrets" but couldn't find anything that seemed to apply to this problem. I've heard that "Dead Mac Scrolls" may have some useful information, perhaps I should look for a copy.

Any ideas/advice? I could set the innards aside and try my hand at a non-destructive casemod of some sort, but I'd like to try resurrecting the 128 first if it's possible. Thanks!

Here are some images of the sad 128:

With flash:

w/o flash:

or check out the photoset here:

 

[jsarchibald]

It reminds me of Simasimac, which usually discusses the SE/30 model. For that model, it says its a RAM issue. Its probably not relative between these models, but it could be faulty RAM (which is obviously soldered onto this board).

However, another forum member had faulty RAM on his early model Mac, and it came up with the Sad Mac and a code that allowed him to find the faulty RAM, which happened multiple times until it was repaired. Hopefully someone else here can help.

 

[gubbish]

Thanks for the reply,

I'm hoping it is just bad RAM. That at least would be straightforward to replace. Seems like many types of old computers fall victim to bad RAM so it wouldn't be too surprising if this was the case.

Luckily there's an electronics distributor just down the road from me that sells 4164 and 41256 DRAM chips, either of which (I think!) can be used in a Mac 128.

Incidentally, about the RAM for the Mac 128 - Do you happen to know if it is 4164 DRAM or 4264?

I believe I've seen some reference to both and I'm not sure which it actually is. I haven't yet opened a 128 to see for myself, but hope to do this as soon as I can clear a space to work on it!

Thanks again.

 

[Byrd]

This is a similar symptom to my faulty 128K, with thick vertical lines and some video corruption (sort of like dead pixels) there abouts on the CRT. It did display a Sad Mac error, and I was happy to report that the two RAM modules replaced did repair the Mac to full working order.

viewtopic.php?f=7&t=14580

Before desoldering components, I'd look into cleaning the board with something like meth spirits, and double checking all components are properly seated etc.

JB

 

[Solvalou]

I had the same issue on my SE/30, sadly its a pretty broad range that could be wrong but chances are its the caps or the logic board at fault.

 

[Macintosh128k]

Firstly confirm that it is the logic board, rather than the analog board by swapping it out with the one from your other known working 128 that you mentioned. After you have confirmed this as others have mentioned you can move onto cleaning and inspecting the boards capacitors.

If it comes to the point where you need to desolder drams and replace you need Mt 4264-20 ICs , the earlier Apple boards use Apple branded ICs

 

[JDW]

Every vintage compact Mac owner should purchase his own personal copy of the Dead Mac Scrolls. I did.

Okay, I won't be stingy...

Page 65 says:

Symptoms: There is no startup bong. The display is filled with alternating white-and-black vertical bars.

Typical History: The problem occurred right after a disk drive/ROM upgrade or SCSI upgrade.

Solution: Verify that the ROM chips at board locations D6 and D8 are not reversed, backwards, or otherwise incorrect installed.

But the garbage pixels at the right side of the CRT indicates another, separate problem that stems from the Analog Board. It could be a bad ground connection (ground not connected well to the metal chassis), or it could be that the flyback transform had been replaced in the past but the BU406 transistor was not replaced (and needs to be replaced). Even so, the bad ground and bad BU406 tend to produce a CRT right-side "wiggle" (like a worm) rather than garbage pixels (as you photo indicates). Therefore, it could be some other problem, yet a problem that is still somewhere on the Analog Board. You can use your "Macintosh Repair and Upgrade Secrets" book to guide you through various Analog Board tests and repairs to eliminate that.

But first check the ROMs. Who knows. Maybe fixing that will also solve the right-side pixel garbage too.

 

[gubbish]

Thanks very much for your help, everyone.

Looks like I have a little project on my hands here, but that's a big part of the fun of this hobby.

First thing I'll do will be to check the analog board with a known good one by swapping in a logic board.

I have the other 128k as I mentioned, and a few working Mac Pluses in reserve, so I could use one of these logic boards to test.

Hopefully I can incriminate or rule out the analog board and then I'll go from there.

Also searching for "Dead Mac Scrolls" as we speak! Definitely seems too useful to not have a copy.

Thanks again and I will keep you posted on my progress.

 

[Concorde1993]

Also searching for "Dead Mac Scrolls" as we speak! Definitely seems too useful to not have a copy.

Is that still in print? Or does one have to purchase a used copy?

 

[gubbish]

Just ordered my copy from a seller on amazon - about $6 including shipping. I believe it's out of print, but seems relatively plentiful.

 

[techknight]

Depends on WHICH ram chips are bad.

As the screen refresh uses a certain address of RAM, if that IC is bad, youll have this issue.

or if one of the address decoders is toast, or PAL ICs is toast, youll have this issue as well.

 

[Mac128]

If it comes to the point where you need to desolder drams and replace you need Mt 4264-20 ICs , the earlier Apple boards use Apple branded ICs

What exactly does this mean? DRAMs are DRAMs. The early DRAMs were Hitachi 4864, and the later large Apple branded chips were 4264 as well. Apple used DRAM from many sources. Larry Pina even indicates 4164 works in the 128K. The presence of an Apple silkscreen only indicates Apple got a deal on a batch of it, not any kind of special specs.

Gubbish - I have a 128K logic board with a similar problem with the stripes and garbage on the right side of the screen. In my case, it was a 128K upgraded to a 512K, and has since had it's mini-Mux removed, but the board was not repaired. I presume you've opened your 128K by now and inspected the logic board. If not, you should definitely do so, as the problem may be just that evident.

FYI, 256 DRAM chips are for 512K, but can also be used without a multiplexing array to achieve 128K, though I'm not sure I would mix-N-match them.

 

[trag]

Any flat (ribbon) cables sneaking out of the vents on the side of the machine, or above the ports in back? Or has the battery cover perhaps been replaced with a DB-25 connector?

The symptoms suggest missing ROM chips, or poorly seated ROMs. This could happen normally, or there could be an upgrade in the machine which plugs into the ROM sockets, which has come loose.

If you find a card in there with a cable that terminates in a connector that looks like a mini-centronics (but isn't) please let me know. It may be the docking card for an Outbound Laptop Model 125. If it is, there will be no ROMs in the machine, but the docking card is unobtainium and I've been looking for one for a while.

More likely, there's a SCSI upgrade in there that has come loose, but I keep hoping for the docking card...

 

[gubbish]

Hi,

Thanks again for the ideas on the sad 128k mac -

Pesky work and life concerns have kept me from opening up the 128, but I hope to do so within the next few days.

I got my copy of Dead Mac Scrolls, and as mentioned before on p. 65 it discusses a problem that sounds very much like this (vertical lines, no startup bong). It does mention, though, that the particular problem happens on a 512k logic board. Perhaps this mac was upgraded in the past. No way to know until it's opened up, so here's hoping I can find an empty table and a few spare hours in the very near future!

Sorry to say it doesn't look like there are any ribbon cables or DB-25 connectors, but I will certainly check for them when I get to open up the machine.

Also, was doing some investigation on various 64kbit DRAMS, and wanted to share my findings in case anyone was interested. As Mac128 mentioned, Larry Pina indicates that 4164 DRAMS work in the 128k and just wanted to check the pinouts and specs to confirm this -

Found a datasheet for the MT4264 (micron) DRAMS here: http://www.datasheetdownload.com/download.php?id=559895

And here's a 4164, which you can get from Jameco: http://www.jameco.com/Jameco/Products/ProdDS/41662.pdf

The pinouts are the same so it definitely seems like they would be interchangeable. Looks like the 41256 is the same except that pin 1 is the high address bit instead of no connection like in the 4164. Not sure what affect if any this would have in the use of it as a replacement.

Just wanted to share that in case it's useful to anyone. Will be back with details when I open up the 128. Thanks again!

 

[Mac128]

The reason Pina says on page 65 that it is a 512K board, is because there is typically no other reason to remove the ROMs from a 128K board.* That is not always indicative of the problem. As techknight points out, there could be several other reasons for this problem, which had not yet come to light at the time Pina wrote that book, but only became problematic 20 years later. Heck they could have even popped out during shipping.

Also, the 41256 chip pin 1 being connected to the high address bit, has absolutely no affect on a 128K and causes it to function as a 64k dram. Since pin 1 is not connected on a 128K, or at least not connected to a decoding matrix, the extra RAM of the 256k is not recognized. However, I have never mixed and matched these chips. They should function properly together, but why needlessly create potential problems. Also, I'm not sure you should mix and match any chip types in any kind of permanent way. As Pina suggests, if you do have to replace any chips, replace them with sockets, that way you can experiment with whatever chips you had ... Although i seem to recall someone mentioning that all of the chips should be docketed if any.

*The other reason Pina does not cover for some reason, is that there was a ROM revision necessary for early Macs that had their 400K drives replaced with newer 400K drives.

 

[gubbish]

Thanks for the info Mac128. Agreed about not mixing chip types, unless of course there's salsa involved.

I also remember something about all or none of the chips being socketed, something about the small difference in lead length between socketed/unsocketed chips causing problems.

The torx driver is coming out, hopefully tomorrow or thursday.. looking forward to investigating this further.

Thanks again for the help.

 

[Macintosh128k]

What exactly does this mean? DRAMs are DRAMs. The early DRAMs were Hitachi 4864, and the later large Apple branded chips were 4264 as well. Apple used DRAM from many sources. Larry Pina even indicates 4164 works in the 128K. The presence of an Apple silkscreen only indicates Apple got a deal on a batch of it, not any kind of special specs.

I was referring to the 200ns access time of the 4264 chips Apple used, other computers at the time used different access time DRAMs,

 

[Mac128]

Pina recommends 150ns DRAMs. However, nothing lower. 200ns is the minimum standard required by Apple.

 

[gubbish]

Well, I had some work I needed to do tonight, and I was so desperate to avoid doing it that I cracked open the 128 and started poking around.

Opened it up to discover a dusty, nasty situation inside - there was quite a bit of dust and debris inside the case. There was even what looked like a bit of a leaf or pine needle lodged into a corner of the CRT, that can't be good. It must have been stored in a dirty garage for some time.

(look for the leaf at the bottom of this picture!)

Pulled out the logic board to discover a similar situation. The board was very dusty with a fine whitish dust. But it was clear that this board has not been upgraded to 512k, it has soldered MT4264 chips. ROMs are in the right way but may need reseating. With so much dust it seems like a short could be possible.

Next step: Opened up a known working Mac Plus, and pulled out the logic board. Connected it to the 128's analog board, fired it up, and...

Success! Started right up, booted from a floppy (external, the internal drive is still gunked up).

So it looks like the analog board in the 128 is ok. That being eliminated, seems like the first obvious step is to clean the board off, it certainly needs it. Byrd mentioned meth spirits - might look into that. I've also used isopropyl alcohol when cleaning circuit boards with some success. Perhaps this is the same as meth spirits and I've forgotten my high school chemistry..

In addition to the condition of the board, I did notice one odd thing on the logic board. There was what looked like a resistor array connected to some of the pins on the IC at D-15 -

It was connected to 4 of the pins of the chip (8432, SYP6522) and one of the leads of the component (capacitor?) at C30. Some of the pins of the resistor array were clipped off and not connected. This may be normal, but it stood out as a bit odd.. Is this a normal component on a 128 logic board?

Reading through the Macintosh R&U Secrets book again, I saw a possible clue in an unexpected section of the book. Under Lisa/Mac XL repairs, figure 13-14 shows a screen pattern that looks very much like what I had - thick vertical bars. From the book, "This pattern indicates total RAM failure. On the Lisa, Mac XL, Mac Plus, and Mac SE it generally means the cards and/or SIMMs are missing. On the 128K to 512Ke with certain memory upgrades, it generally indicates a problem with the 68000 chip." Well, it didn't look like there were any memory upgrades on this board, but it's a curious similarity. Perhaps if many of the RAM chips are bad, it can't even muster the Sad Mac error code.. I suppose CPU error is possible too.

I think next steps for this are a good cleaning, reseat the socketed ROMs, and try again. I'm hoping for at least a sad mac code. If anyone has any ideas based on the new information, or if you think of anything I should look for, please let me know, thanks!