macintosh plus - Page 1
Forum section: electronics / repair

author: screwbreaker
author_rank: Regular Contributor
timestamp: April 07, 2016, 09:47:42 am
content: Hello to everyone, I'm sorry to do my first post about a repair questionFirst to all, forgive me for my bad EnglishI'm trying to repair an old macintosh plus:I got it with a really common problem, a blown up main filter capacitor.I have replaced it, cleaned the board, checked for spread metal. I also checked the capacitors in the power board, due the ones near the filter capacitor gets some scratch.According to various manuals found online I checked the voltages, 5V, 12V , -12V on the power board before reconnect the logic board, and after I checked them again on the external drive connector.Everything seems ok, but the macintosh refuse to start up. I only got an infinite loop of initial bong! And a black screen.At this point I’ve tried a lot of checks, but everything looks good, the caps on the logic board are ok, I also cleaned all the socketed ICs, the SIMMs pins and all the other connectors. I also resoldered the connectors on the power and the logic board.The only thing I got are some raster lines, increasing the luminosity trimmer on the back of the power board.The black screen issue seems related to the power board, but I also got a infinite Bong! from the logic board. So I decided to check if some video signal was generated from the logic board. And this is what I got:Channel 1 is the video singal, CH2 Hsync and CH3 Vsync.The Vsync and Hsync signals are ok, and I got some starts of video signal on the power up, then nothing. If the black screen was caused by a logic board fault, the power board can be ok.For a double check I powered up the logic board with an external PSU and the result was the same.I also checked the speaker line and i got the same eternal bong pattern.So the logic board issue is not related to the power board. At this point I checked for a possible cause of the eternal Bong! the first thing I thought was to some reset problem.And after a lot of tests I finally got this:There is really some reset issue, for some reason the reset signal periodically falls and the machine never start up.I looked the schematics in search of some possible issue. I don't understand exactly how the reset is implemented, but I supposed the SND chip is the one who generate the reset signal. When the reset switch SW2 is pressed, the pin 6 of the SND chip read the voltage drop and put the pin 5 to low. I supposeAnyway the problem must be generated somewhere on the reset line, so, the guilty must be one of the chips on the line, the SND chip, the U2A filter, or one of the other chip.For practical reasons I started with the SND chip. I checked the pin 6 in search of some fluctuation of the input, but there wasn't. The problem don't seem to came from this path.So I decided to lift the pin 5 of the SND chip, leaving the reset line pulled up to 5V by the R35. In this way I got some strange sound instead of a classic Bong, perhaps due to the fluctuating pin 5? So I decided to remove the SND chip, because according to the schematics it does not seem to do anything special, except managing the reset.In this way I got some video signalBut the screen is still blackI also got some strange segmented line instead of a single line as before.I'm very confused.I can't understand what kind of problem I have here. And I can't find anything specific for the logic board troubleshooting. The only information I got are mainly related to the power board.I hope someone with more skills and experience than me can help in this case.Thanks to everyone, and sorry for the long and not easy readable post

author: stj
author_rank: Super Contributor
timestamp: April 07, 2016, 11:47:28 am
content: if it's like newer mac's then there is a lithium battery that must work, and once you have that confirmed you reset the pram. (cmos ram)

author: CatCow
author_rank: Contributor
timestamp: April 07, 2016, 03:35:56 pm
content: Quote from: stj on April 07, 2016, 11:47:28 amA dead PRAM battery will typically result in no response when powering on. The Plus has a battery, and should be checked, but the video issues indicate that the battery is at the very least not the primary failure. Bad RAM can also cause similar issues, and I once had to fix an LC that looked like bad RAM or a dead battery but turned out to be a bad PSU(even though the main rails had the correct voltage, I think there must have been a sense pin that wasn't talking but that was a long time ago and my memory is a little fuzzy).Some Google searches came up with some handy info. There are a couple of old books that are handy to have if you deal with a lot of classic Macs, one being The Dead Mac Scrolls. A second book appears to now be online as a PDF(seems unlikely to be a "legal" copy, but it's available out there), called Macintosh Repair and Upgrade Secrets. On page 105 of that book it describes the horizontal line on the screen as being the rather obvious loss of the vertical sweep. Check the solder connections on connector J4, and check for continuity between ends of the green wire that comes out of that connector. If that all tests good than they say the problem is on the analog board at Q1 and Q2, labeled Q4 on international models.Oh, and put that SND chip back in

author: switch998
author_rank: Contributor
timestamp: April 07, 2016, 04:16:27 pm
content: Did you check this forum?https://68kmla.orgThose guys know everything about everything when it comes to vintage macs.

author: kripton2035
author_rank: Super Contributor
timestamp: April 07, 2016, 04:37:17 pm
content: I dealed with these failure a loooooonnnnngggg time ago ...if I remember good, seems to me it's a bad soldier problemyou re-soldered the power supply connectors, may be you should inspect the power supply board for bad soldiers (around high voltage section or so ?)good luck.

author: screwbreaker
author_rank: Regular Contributor
timestamp: April 08, 2016, 09:39:32 pm
content: Thank you all for the repliesQuote from: stj on April 07, 2016, 11:47:28 amYes there is a battery on the back of the mac. And of course it's deadI've done some test with a "standard" 4.5V battery.And I got no difference with or without the battery.Quote from: CatCow on April 07, 2016, 03:35:56 pmI thought that, too. As a test I've put in the R9 (ONE ROW) resistor in order to force the mac to use just one of the two memory bank. In this way I've tested every combination of the SIMMs, two at a time. Without resultsAnd I can't believe that all of the 4 SIMMs are deadI've also tried without the ram. According to the information I got on internet in this case I have to got an error message. As I read this mac perform a lot of checks on boot. A ram check, a ROM check, and other system checks, and in any case it must show a sad face and an error code. But this cannot be true, or it's true on some other mac models. I don't know, this is my first macA ram fault still possible, the SIMMs became very hot when I power the mac on. And as I remember this type of ram don't heat up so much. But they still relatively cool, they are hot only compared to the other IC in the system, to be clear they became hot like the 68000.Quote from: CatCow on April 07, 2016, 03:35:56 pmI've found this books, and some other. they are really useful, but in this case I can't find enough information.I got the black screen and the reset issue even if I power up the logic board with an external PSU. So there must be something wrong in the logic board itself.I think I got the horizontal line because I've tweaked the brightness control on the logic board. In the service manual there is a section for the brightness adjustment, and the manual say:"...Turn the brightness control fully counter-clockwise so thatwhite lines are visible..."I've already cleaned and resoldered the J4 connector, and all other connectors. I think they are good, bur I can check them again.Quote from: CatCow on April 07, 2016, 03:35:56 pmOf courseJust ...As I mentioned before, I've done some other tests with and without the battery.And, with the SND chip I got the eternal Bong, the reset issue. But without I got some strange things. Sometimes I got a strange loop, as if the mac tries to boot up but it fails and then tries it again and again, something like a reset, but there isn't a reset signal on the reset line, or I can't see it.Some other times I got another strange boot with just a tiny video signal from time to time.And some other times I got a single white line on the screen, without any video signal.These three behaviours seems completely casual.OK, I have one IC missing on the board, so nothing of this can be important. But I've reported them.Thanks to all again. I will follow all of yours tips.

author: screwbreaker
author_rank: Regular Contributor
timestamp: July 19, 2016, 05:44:45 pm
content: Fixed!The problems was the two ROMs on the logic board and the JFET Q5 on the vertical sweep.

author: CJay
author_rank: Super Contributor
timestamp: July 19, 2016, 05:57:12 pm
content: Fantastic, I was just about to weigh in and tell you to stop messing around with the logic as the line looked primarily like a vertical deflection problem.

author: chunkynuts74
author_rank: Newbie
timestamp: May 09, 2020, 08:23:50 am
content: Sorry to resurrect such an old thread but there was too much overlap with the problems I'm currently having with my Macintosh Plus:On startup, I get no video and a continuous boot chime.Analogue Board seems to be working fine - getting solid 5V and +/- 12V at the external floppy port and solder joints/caps all look good.This points to the logic board, which leads me to the problem outlined in this thread.I would be very interested to know the details of the fix :Quote

author: screwbreaker
author_rank: Regular Contributor
timestamp: May 09, 2020, 10:49:38 am
content: Try the same steps I did. Check if you have a video signal and try to replace the two ROMs.

author: Peacefrog
author_rank: Contributor
timestamp: May 09, 2020, 01:28:43 pm
content: Out of interest, how did you find the ROMs were part of the problem?

author: screwbreaker
author_rank: Regular Contributor
timestamp: May 09, 2020, 07:29:55 pm
content: By chance. They were the only components easy to replace. I also knew that the logic board was doing something, so most likely the CPU was ok. And according to some research they can get corrupted sometimes.

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: May 09, 2020, 10:36:21 pm
content: And if you can't readily get new ROMs, try pulling yours out and putting them back in. "Reseating" RAM (and, to a lesser extent, expansion cards) was the go-to first intervention for mysterious hardware problems back in the day.

author: chunkynuts74
author_rank: Newbie
timestamp: May 10, 2020, 01:43:00 pm
content: Thanks everyone for the replies.I have tried reseating the ROMs and cleaning up the contacts. Still having the same problem.What's the best way of going about getting fresh ROMs?This post -https://oldcrap.org/2019/03/22/macintosh-plus/- suggests burning the ROM files to an EEPROM (W27C512-45Z).Trouble is, I don't have an EPROM programmer.

author: cdev
author_rank: Super Contributor
timestamp: May 10, 2020, 08:41:55 pm
content: Good luck, its a great machine. Really brings back memories to see one.

author: ParzivalR
author_rank: Newbie
timestamp: May 13, 2020, 04:17:44 pm
content: Hello everyone!I introduce myself, my name is Rodrigo. I live in Argentina, so I apologize if my English is bad.First, I apologize for asking for help without having helped before. I've been reading forums since 2017, but I've only just had time to get back to work on the Mac during quarantine.In 2017 I had the joy of finding a forgotten Macintosh Plus (Apple is not very common in my country) in an old warehouse. He had suffered a lot, he had the rear battery door with the battery burst and a lot of dirt. When turned on, the dreaded SadMac appeared with a code that I did not find in the repair manuals. Since poor Mac needed a shower, I started to take it apart. I washed its plastic parts, and removed all the corrosion that was possible (leaving marks on the analog board that do not affect its operation). But, due to my clumsiness, I made a mistake in testing. I forgot to connect the CRT ground wire, to which the Mac responded with sparks inside the Electron Gun and smoke coming from the analog board. I turned it off quickly but the damage was already done. I proceeded to plug the cable into the corner of the CRT, and turned it on again. But the Macintosh now only managed to show a small line to the center of the screen. I noticed that it was the same width as the SadMac logo. With the error code noted above, I started to see its possible causes. Which led me to the HIGH ROM. I got the file to flash an Eprom in a forum, and upon posting it, the Mac booted up, but showing only the top of the screen and a horizontal line in the middle. In the repair books, it specifies R3 and Q1 as causing this problem. But having analyzed them off the circuit, I concluded that they were fine. I do not remember when it happened, but the central line shifted higher, since there is now only an image in the upper third, no longer coinciding with the other cases raised in the books. I have replaced: R3; R2; CR2; C5, Q7, Q4 (The 2n4401 for a BC337) but everything remains the same. I also got a full identical CRT, but it displays the same way. Unfortunately I don't have an oscilloscope, nor the possibility of getting a replacement MPSU51 or MPSU01. I've started parsing two equivalents for these, but I'm not entirely sure. TIP117 for MPSU51 and TIP112 for MPSU01.Data that may be useful:-Analog board: 820-0082-E 1986-FlyBack: 157-0042C-Input Voltage: 110 (Non international version)Hope someone can help me.A very big greeting to all.

author: cdev
author_rank: Super Contributor
timestamp: May 14, 2020, 11:30:00 am
content: Happy Mac!Four Megs of RAM. (Isn't it amazing what they did with only 4M of RAM?)

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: May 14, 2020, 10:32:37 pm
content: Yes! The greatest benefit of > 1 MiB RAM was runningMultiFinder. Although it made the OS even more likely to crash (no MMU), it was convenient.ParzivalR, repairing the analogue board will be difficult even with an oscilloscope. Maybe you can finda hackerspace near you?

author: cdev
author_rank: Super Contributor
timestamp: May 15, 2020, 01:59:09 am
content: Do you have it all working now?You can now fid all those old ROMS and tons of software for old macs on archive.orgIts mostly abandonware. I think Apple even put the entire original Mac OS 5-9.01 and Classic (OS 9.1) for Power Macsonline somewhere for people with older Power Macs and 68000 machines to download.----------------------------------I gave my old Mac Plus to my mother but she never used it.------------------------------------------Quote from: ParzivalR on May 13, 2020, 04:17:44 pm

author: screwbreaker
author_rank: Regular Contributor
timestamp: May 17, 2020, 10:29:12 am
content: Quote from: ParzivalR on May 13, 2020, 04:17:44 pmIf your logic board is working, and you have an horizontal line on the monitor, try to check the vertical sweep section.Find the schematic and check every component and every connection between them.

author: chunkynuts74
author_rank: Newbie
timestamp: June 16, 2020, 09:40:36 am
content: Just to update on my MacIt seems like it was an issue with the ROM after all.Not having my own EEPROM programmer, I built one with an Arduino following this great tutorial ().Reading the ROMs revealed som flipped bits on the 3420342a LO-ROM.Using the ROM images found here (https://www.nightfallcrew.com/25/04/2014/macintosh-plus-sad-face-repair/) I reprogrammed the offending ROM onto a new pin-out compatible W27C512-45Z chip (https://www.digikey.co.uk/product-detail/en/winbond-electronics/W27C512-45Z/W27C512-45Z-ND/1133334)Putting this new ROM in the Mac resulted in only a single bong, and then to my amazement, the 'no boot disk found' floppy symbol.I don't have a boot disk available, but I do have a Prodrive40 harddrive. Plugging this in and turning on prior to boot doesn't result in any progress passed the 'no boot disk' symbol - so maybe no operating system is actually installed on it. Any tips on diagnosing this further would be great, or if someone has an easy way I can get hold of a boot floppy?Thanks in advance! ﻿

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 16, 2020, 10:34:32 am
content: If you know it's was a working bootable HDD at one point try checking that you hear it spin (stuck heads) and not rattle, changing SCSI ID, pressing "Command-Option-Control-Shift while booting.I've had Quantum Prodrive 40's fail due to SMD electrolytics on their own PCB, replacing them resumes normal operation unless the drive has suffered other problems in the meantime.

author: dr.diesel
author_rank: Super Contributor
timestamp: June 16, 2020, 10:51:06 am
content: I have fond memories of my Mac Plus, it was my first real computer and started my Programming career with Think Pascal.Wish I still had it, my parents tossed it out decades ago.

author: cdev
author_rank: Super Contributor
timestamp: June 20, 2020, 02:26:19 am
content: I would look on Archive.org . There is a ton of old mac software there.Quote from: chunkynuts74 on June 16, 2020, 09:40:36 am

author: james_s
author_rank: Super Contributor
timestamp: June 20, 2020, 02:35:09 am
content: I used to have a Mac Plus, it had a Novy 68020 accelerator in it and an original Laserwriter printer. I actually used that system for all of my college homework because I couldn't get distracted by the (new at the time) internet. Learned a lot of stuff playing with that machine. I eventually sold it several years ago when it came time to prune the collection, I still have a SE/30 I can pull out any time I need to scratch the B&W Mac itch. Fantastic machines for their time, they've held up a lot better than contemporary PCs of the era IMHO though I was never a Mac user back in the day.