Macintosh Portable Troubleshooting

[techknight]

Your power source is still unstable. Did you clean the PCB really well? A good wash down and bake dry is whats needed here. 

Also clean the Hybrid IC really well and lets try this again. This is a classic sign of the PMGR still not functioning properly, or the Hybrid IC still not functioning properly. 

Low input power can do this as well, but the hybrid IC has a window comparator that will lock out the machine on low voltage and prevent this very effect from happening. Unless... of course, the Hybrid of PMGR is malfunctioning. This is very common and sometimes isnt curable. 

 

[Mastergeko4]

Your power source is still unstable. Did you clean the PCB really well? A good wash down and bake dry is whats needed here. 

Also clean the Hybrid IC really well and lets try this again. This is a classic sign of the PMGR still not functioning properly, or the Hybrid IC still not functioning properly. 

Low input power can do this as well, but the hybrid IC has a window comparator that will lock out the machine on low voltage and prevent this very effect from happening. Unless... of course, the Hybrid of PMGR is malfunctioning. This is very common and sometimes isnt curable. 

Alright, thanks. I think I'll attempt to deep clean the board again and let it dry. Thanks.

 

[techknight]

You need to bake dry it, thats key. it drives that electrolyte out of the PCB. 

around 175 degrees F or so, for about 15 to 20 minutes. 

 

[Mastergeko4]

You need to bake dry it, thats key. it drives that electrolyte out of the PCB. 

around 175 degrees F or so, for about 15 to 20 minutes. 

Okay, I'll try this next. Thanks! 

 

[Mastergeko4]

Alright, I’ve cleaned the computer and baked the PBC. The only difference it seems to make now is that it’ll always show signs of life when given power and I don’t have to wait a couple minutes anymore. It does still sad Mac 2-3 times before it’ll actually give me a flashing folder and it’ll still either freeze and restart at boot up, freeze during boot up, freeze when finished booting, or it’ll actually work and let me do things unless it restarts for no reason. It still won’t run on just the battery. The hard drive also still won’t work as the computer will start up but when the hard drive spins, it’ll rapidly click and the screen would flash. What would be a good thing to try now? I’m considering buying a better battery.


View attachment IMG_0891.MOV

 

[techknight]

You need to grab a digital multimeter and put it on DC Volts, take a monitor of the 5V rail and 12V rail to see how stable it is when all this happens, we need to see which rail is faulting. 

 

[Mastergeko4]

You need to grab a digital multimeter and put it on DC Volts, take a monitor of the 5V rail and 12V rail to see how stable it is when all this happens, we need to see which rail is faulting. 

I feel stupid for asking, but where exactly am I putting the meter? 

 

[Stephen_Usher]

For the 5V you can clip the negative probe from your voltmeter to any GND point and then put your positive probe on pin 3 of MOSFET Q4 (at the top right as you look from the front of the PCB. This is always on so should show +5V even if the machine is shut down. Keep monitoring the voltage as you press a key on the keyboard to start the machine up. The voltage shouldn't drop.

For the +12V line, in the same area you will find the two Sony sound chips. Pin 13 on either of these is on the 12V line.

 

[Mastergeko4]

For the 5V you can clip the negative probe from your voltmeter to any GND point and then put your positive probe on pin 3 of MOSFET Q4 (at the top right as you look from the front of the PCB. This is always on so should show +5V even if the machine is shut down. Keep monitoring the voltage as you press a key on the keyboard to start the machine up. The voltage shouldn't drop.

For the +12V line, in the same area you will find the two Sony sound chips. Pin 13 on either of these is on the 12V line.

Thank you! I probed the pins on the chips you told me to do and I don’t think I found the issue. On Q4, it reads 4.9v and rarely 5v however this shouldn’t be that big of an issue. Meanwhile on both sound chips, the highest voltage I could get was 11.5v. I’m not sure if this is a huge issue but let me know as it could be the source of the issue. 

 

[Stephen_Usher]

Those voltages are definitely low relative to my machine. Do they change when you try to wake the machine up?

 

[techknight]

The macintosh portable should solidly be providing around 5.2V. 

It sounds to me you are stiill having issues with the Hybrid IC. Sadly, this is a known issue and I have accumulated a handful of parts boards due to bad Hybrids. 

One last thing to check is make sure your 6V battery is good, AND the battery cover/door is slid and snapped into place. There is a microswitch in there that must make contact to provide the 6V into the logic board, otherwise itll try and run off the 9V battery if there is one. 

@Stephen_Usher You should take a look at the opportunity to clone and reproduce the Hybrid IC as a new PCB. I would do it, but im scrapped for time these days. 

 

[Mastergeko4]

The macintosh portable should solidly be providing around 5.2V. 

It sounds to me you are stiill having issues with the Hybrid IC. Sadly, this is a known issue and I have accumulated a handful of parts boards due to bad Hybrids. 

One last thing to check is make sure your 6V battery is good, AND the battery cover/door is slid and snapped into place. There is a microswitch in there that must make contact to provide the 6V into the logic board, otherwise itll try and run off the 9V battery if there is one. 

@Stephen_Usher You should take a look at the opportunity to clone and reproduce the Hybrid IC as a new PCB. I would do it, but im scrapped for time these days. 

That's a shame that the Hybrid Board is dead but I kinda expected that. I think the last thing I'll try is to buy that battery @LaPorta listed on the previous page. I'll update you guys when I finally finish the project. 

Would there be any possible way to get a replacement Hybrid Board?

Thank you all for your help!

 

[techknight]

Replacement Hybrids will have to be something we make. I ran out of them picking them from parts boards, and my other parts boards have bad hybrids.

I personally own 3 portables, and both non-backlit models have issues with the hybrid. They need changed out with new. I think cap goo gets in there and starts affecting the resistances of the laser etched carbon tracks on the ceramic substrate, or adds parasitic capacitance. But this is a wild guess. the components themselves that are physically soldered on the hybrid are usually ok. 

 

[Stephen_Usher]

Electronically, what does it actually do?

 

[Mastergeko4]

Replacement Hybrids will have to be something we make. I ran out of them picking them from parts boards, and my other parts boards have bad hybrids.

I personally own 3 portables, and both non-backlit models have issues with the hybrid. They need changed out with new. I think cap goo gets in there and starts affecting the resistances of the laser etched carbon tracks on the ceramic substrate, or adds parasitic capacitance. But this is a wild guess. the components themselves that are physically soldered on the hybrid are usually ok. 

That’s interesting. Would their be a way to make a replacement PBC using a website like PCB Way and then just transfer the components? 

 

[techknight]

Electronically, what does it actually do?

It does many things. One, it servers as a -5V voltage inverter. it also serves as the op-amp and reference voltage regulator for the 5V rail. Also, it serves as a window comparator for charge controlling, Sets the system whether the AC adapter is plugged in or not, and if it senses the AC adapter plugged in, it enables the P-Channel mosfet in the rear to allow the 7.5V DC to pass through without a high RDS. 

It also detects for undervoltage lockout. so if the battery voltage falls below a certain point, itll lock out the VREG. so no 5V. 

if the 5V supply is not being regulated properly, 99% of the time its the Hybrid. 

also if the system is running and the System software doesnt detect if a battery is charging or not, its usually the Hybrid there as well. 

 

[techknight]

Here is everything the Hybrid is involved in:

 

[techknight]

The portable schematics can be found in this archive: 

https://archive.org/details/Macintosh68kSchematics

 

[Stephen_Usher]

Sounds like something with a lot of electronics experience, both analogue and digital, might have to work on then.

 

[Mastergeko4]

One other thing I wanted to say. I was wondering if this burnt looking component on the board, Q16, would also be an issue. It looks and smells burnt compared to other similar components on the board so I’m thinking of replacing it. What do you guys think?