LC Power Supply - Died after recap+load

[luRaichu]

I recently picked up a trashbin Macintosh LC and Apple Keyboard II all for $20. The LC was caked with dust, the keyboard was caked with white fur. Cleaned both up and they’re almost good as new. Then I plugged in the power supply. 12v was basically nonexistent. Opened up the power supply, (TDK 699-0153) caps leaked, so I replaced them. I also replaced those CR51 and CR52 diodes, as I thought they were voltage leaky from cap juice because touching the case would give you a “slow” electric shock (what I mean by this is that you could feel it coming and remove your finger before it does). I didn’t replace the 50v cap that’s next to the huge one. Anyways after the recap the PSU would make a fast and continuous ticking noise without load, before the recap the ticking was slower and would fade in and out. I measured after I replaced the caps but before I replaced the diodes and the voltages seemed in spec but fluctuated ~1v. I didn’t know then that the PSU is supposed to tick w/o load, so I went ahead and replaced the diodes. Still ticking w/o load. I didn’t measure the voltages after the diode replacement and just went ahead to connect it to the motherboard. I left it a few seconds, no boot chime or anything… While connected, I measured the voltages. It was only giving 0.1v on both rails! I disconnected the PSU from the motherboard and ran it w/o load. It ticks only once, still 0.1v. So then I focused my attention on the motherboard. I had a little charger brick and a USB cable that gives you the power from it. The brick is 5v, 3.1A… close enough I thought. I connected this to the 5v rail on the motherboard and got nothing. Will this motherboard make video/chimes only with 5v? Also the motherboard’s caps all leaked. I teared them off last night. I’m not a soldering wizard by any means so it’ll be a headache to put new SMD caps on. The caps I got don’t even have long legs like the originals! They barely extend past the plastic square. The lone cap in the photo was a test that night to see how hard it is to solder on caps.
All in all, I think I’ll replace the PSU with a Mean Well RPT-60A if I can’t get the TDK to actually work. The Mean Well seems to say it gives 4A. The TDK gives 3.24A. Will my board be damaged by higher amperage? Does a 1A difference really matter in electronics?

When I got the LC, the motherboard was very dusty and the dust and cap juice combined to make a sticky goo. I cleaned it up but I wasn’t able to clean anything under the chips. I want to dishwash this board… but my dishwasher’s broken and I won’t have it for months. I want to dishwash the board before I recap, but I don’t want to wait months. I also don’t want mineral traces on the board nor do I want it to rust and die in a couple years, I believe dishwasher detergent will solve that. If only…

 

[joshc]

You need to use flux on the new solder joints to avoid dry joints. From the photos you've taken of your attempt on the logicboard and power supply, those joints look dry and won't be making good contact with the solder pads.

On the TDK power supply, you need to replace the small capacitor on the high voltage side of the board as well (near the really large capacitor) in order for it to be fully functional.

Don't use a dishwasher to clean a board - brush/soak it with soapy water in a tub, and then rinse it with isopropyl alcohol (99%) and leave to dry.

These power supplies don't run without load if I remember correctly, so it is expected for it to not work if there's no load.

There's no point testing with that logicboard until all the caps have been replaced and all the cap goo has been removed.

If you're not confident with SMD work yet, I really recommend practicing on something you may care less about - you can get trash boards from eBay and practice on those instead.

Take the time to learn some soldering skill from YouTube, that's what I did.

 

[Phipli]

The Mean Well seems to say it gives 4A. The TDK gives 3.24A.

The current is the maximum that can be drawn from the power supply, it doesn't always force that much out, so exceeding the LC current rating is a good thing, the current flow will still be the same from either (working) power supply, but the 4A one will be running further from its limit.

 

[luRaichu]

I resoldered the new SMD cap using flux. Much better isn’t it?

 

[joshc]

Better but the left side still looks a bit rough? What sort of solder/flux are you using?

 

[luRaichu]

Well, I just finished recapping my first motherboard!
Behold my tolerable skill of soldering.
Please take note that some joints appear dry, it’s probably because of the lighting in this pic but I did make sure every cap has a very solid connection.
I feel sort of pressed on whether I should take a risk and buy that 8.2uf 50v cap or just get a whole new PSU altogether. Because there’s no guarantee that the TDK one will work with that cap. Not to mention I did a quick check online and it seems like caps of 8.2uf 50v specifications are hard to find.

I use no-name solder and flux that was part of a cheapass soldering kit from Amazon, It was gifted to me.
Bully me for this. I deserve it.

 

[Phipli]

View attachment 58939
Well, I just finished recapping my first motherboard!
Behold my tolerable skill of soldering.
Please take note that some joints appear dry, it’s probably because of the lighting in this pic but I did make sure every cap has a very solid connection.
I feel sort of pressed on whether I should take a risk and buy that 8.2uf 50v cap or just get a whole new PSU altogether. Because there’s no guarantee that the TDK one will work with that cap. Not to mention I did a quick check online and it seems like caps of 8.2uf 50v specifications are hard to find.

I use no-name solder and flux that was part of a cheapass soldering kit from Amazon, It was gifted to me.
Bully me for this. I deserve it.

View attachment 58941

Excellent! The worst part is building the courage to do it, and knowing when to stop when it is going badly.

I find most solder is fine, but I'd probably get some better flux, nice stuff isn't too expensive and lasts for ages. Make sure you use "no clean" flux in case you miss a bit under a chip.

On that, the only comment I'd make about the soldering is a drop of liquid flux on each pad and a 1 second tap with the iron would tidy up the solder. Its generally good to use plenty of flux. It makes everything easier and results in better, neater connections.

Alround awesome first logic board though. Any board that boots is a success. One that has sound out is always a bonus!

 

[joshc]

Looks much better. Good luck with getting it booting!

 

[luRaichu]

Is there a way for me to know if the board works, with just 5v? I read the schematics and audio needs 12v. I’m not sure if the entire board can boot solely on 5v. I hooked it up to a VGA LCD with a homemade adapter, gave it 5v (no ground though) and got no video signal,
no audio of course. I then found out the adapter I made absolutely sucks! I thought $8 too much for a new adapter of that type.

TL;DR, I have no idea if it works.

 

[Phipli]

Is there a way for me to know if the board works, with just 5v? I read the schematics and audio needs 12v. I’m not sure if the entire board can boot on 5v. I hooked it up to a VGA LCD with a homemade adapter, gave it 5v (no ground though) and got no video signal,
no audio of course.

It should boot with just 5v... to check if it works you could watch the modem port for activity on the TX pair? Or wait for a known good video adapter.

Note the video adapter generally needs to be a special 10 switch one for the LC - its video is a bit old fashioned and you need an adapter that supports adapting the sync to different types. My LCD runs from my LC happily in composite sync settings. See attached.

Sync is probably where your adapter falls down.

 

[Phipli]

to check if it works you could watch the modem port for activity on the TX pair?

This is dumb - the serial needs the -5 too.

With only 5v you're really needing video I think.

 

[luRaichu]

This is dumb - the serial needs the -5 too.

With only 5v you're really needing video I think.

Not sure what you mean by the last line - but those video adapters with dip switches are $20!! Ridiculous! What do they even do besides modifying sense lines? ADB mice are a little pricey too. I only have the keyboard.

 

[Phipli]

Not sure what you mean by the last line - but those video adapters with dip switches are $20!! Ridiculous! What do they even do besides modifying sense lines? ADB mice are a little pricey too. I only have the keyboard.

Some of the early desktop macs output video that has a sync mode that isn't supported by many modern monitors. Its best to have a 10 switch adapter because they offer the ability to switch what type of sync mode the monitor gets. Seperate, composite, sync on green etc.

I haven't read up on the LC's supported video modes, but those adapters are... well, mandatory with many macs up until about 1991.

Someone who knows the LC better than me will be able to tell you if they work at all with modern lcds without a 10 switch adapter.

 

[Phipli]

I tested all of the adapters I own. The LC is much more forgiving than some of my other Macs. It was just bad luck that it didn't work with the first adapter I tried. It even worked with a switchless one... but... be warned. I'm using an early 2000s ViewSonic LCD that I specifically use on old macs because of its excellent compatibility with odd video signals.

 

[luRaichu]

Lol, I bought a 2004 Viewsonic VG510s for $5 at my local thrift store, just for this LC. I specifically bought an old flatscreen because I heard they support weird refresh rates. And it was the cheapest monitor they had in store! I even got it to display video from an iPhone using an A/V adapter. I tested a TV box though, and it said “OUT OF RANGE”, then gave you a green/red screen. I used an HDMI->DVI adapter, wonder what causes that.

Bringing this conversation back to Macs, do you know if this video adapter will work?

Or this one?

https://www.amazon.com/C2G-Cables-02902-Female-Adapter/dp/B0002J1JAE/

 

[GRudolf94]

The NEC one probably has the sense lines hardwired into 1152*870 - which is a resolution weird monitors may not like. The amazon one sounds hardwired at VGA. If you wouldn't mind that...

I'd hold out for one that has dipswitches and allow manipulation of sense codes, but, like @Phipli has shown, YMMV.

 

[luRaichu]

Sorry for being late (the site being down hasn’t helped either) but anyways I got the LC to work a couple days ago. Cap juice had weakened copper pads in the PSU which I destroyed when taking an old diode out. So I connected the new diode to good pads using jumper wires and everything works now. I bought that DIP-less video adapter from Amazon and it does work with my LC and monitor.

With the adapter, it outputs at 640x480 and the refresh rates seem VESA compatible.

 

[luRaichu]

Alright so I’m having a bit of trouble here. I got an ADB mouse 2 days ago and started fooling around with my LC. I had some 1.44MB floppies that I tried to format but the machine always failed at “re-verifying format”, not sure why. Anyways I tried to run Norton Benchmark or something but it said my disk cache needed to 128K. I set it to that but then shut down the machine as it was late at night.
Then next morning, I powered on the machine and was surprised to see that it couldn’t find a bootable disk. So I think the SCSI drive has finally died, or become corrupted. So I guess I gotta go buy a SCSI emulator now…. Too bad most pre-assembled BlueSCSI’s out there seem to cost a pretty penny, and the cheap ones are out of stock! I will probably end up building one myself, but idk how I’ll get the PCB. Please enlighten me on that specific matter.

 

[cheesestraws]

You are jumping to conclusions. Boot from a floppy first and see whether the hard disc mounts. If it does, try re-blessing the System Folder by dragging the Finder out of the System Folder and back into it again.

 

[luRaichu]

I probably would’ve already tried to give the hard drive CPR if I had a bootable floppy, but I don’t (I would have made one already if the floppy drive was all correct that night. After attempting to format 3 disks it self-injected without a disk inserted; I saved that repair for the next morning). So in my mind I might as well just get a replacement for the HD anyways! Should I really continue bothering with a 30 year old hard disk that’s doomed to fail sooner or later? I’m not even convinced the floppy drive is fully operational either, so at least having a BlueSCSI would allow me to install software without it.