Is it my Logic Boards (IIvx, IIci, Performa 600, and Quadra 650) or my Power Supply (Delta SMP-120EB)?

[jdmcs]

On my livestream last night, I attempted to recap the Delta SMP-120EB power supply that was in my Performa 600. And after initially forgetting to reconnect the mains power connector, I measured 4.97V on the +5V standby output... yay!

However, my joy quickly faded when I tried to power up the Quadra 650 logic board with this power supply (chosen because it doesn't have leaky electrolytic capacitors), and I could not get it to power up. Knowing that tantalum capacitors can fail shorted, I measured the resistance of the voltage rails on the logic board, and sure enough, had 12ohms between the +5VDC (not standby) and ground.

So I tried the power supply on my IIvx logic board, and it powered up for a second or two and shut off. I again measured resistances on the logic board, and found that I had 15ohms between the +5VDC (not standby) and ground. OK, seems something might be shorted on that board, I'll figure out what when I recap it.

Next up was my Performa 600 logic board, which I didn't want to use because the electrolytic leakage is worse on it than the IIvx logic board. The power supply did the same thing, and I then again measured 15ohms between the +5VDC (not standby) and ground. This is beginning to look suspicious - three logic boards shorted in the same way, what are the odds?

So finally I decided to check my "parts" IIci logic board. Given that it was battery bombed, I dared not plug it in. However, I measured 18ohms between the +5VDC (not standby) and ground.

At this point, I'm beginning to wonder if that resistance measurement is normal. However, I have exhausted all of the logic boards in my possession that use this style power supply, and ideally would measure the same resistance on a booting logic board that has already been recapped.

To help me figure out where the problem is:

1. Can anyone measure the resistance between +5VDC (pins 2-4) and ground (pin 5) on a working, booting logic board of one of these four types?
2. Does anyone know if there are schematics for the IIvx/Performa 600 or even the Quadra 650... or at least know which capacitor(s) are the main filter caps for the 5V rail?
3. Does anyone know of a starting place to look at on the Delta SMP-120EB?

 

[jack 68k]

I checked pins 2-4 (+5 VDC) vs pin 5 (ground) on a working IIci logic board and measured 10.8 ohms.

 

[jdmcs]

Looks like I need to crack the power supply back open to double-check my work and check for damaged components inside.

There was a power resistor in heat shrink that’s my number one suspect. The switching MOSFETs are my second suspect.

 

[jdmcs]

Update: Sometimes it helps to set a project aside for a few weeks and then inspect your work again… I discovered that I had desoldered the leg of a resistor.

The power supply is now functional, I tested it on the Performa 600 Logic board.

I guess the relatively low resistances measured on the +5V rail is normal for these systems.

 

[chbi]

Hi! Watched your YT video a few days ago @jdmcs, very informative! I have two boards (a IIvi and a Performa 600 board). Non of them working, the IIvi is not recapped and won't boot at all, the Performa 600 (recapped) powers on (via button and keyboard) but doesn't chime. I'm starting to suspect the Delta PSU but not sure how to properly check it. Measuring 5.01V and 11.85V on the HDD power supply connector but I am unsure how to check the other voltage (-12V) and if it's strictly needed for booting these boards?
Both boards worked in the past. But stopped working quite close in time, both tested in the same machine using the same psu.

The Performa 600 board looked pristine and the IIvi had definite leakage.

For the record I managed to recap a dead color classic and revive it (my first) so I'm quite new to this.

Any advice is greatly appreciated!

 

[jdmcs]

Hi! Watched your YT video a few days ago @jdmcs, very informative! I have two boards (a IIvi and a Performa 600 board). Non of them working, the IIvi is not recapped and won't boot at all, the Performa 600 (recapped) powers on (via button and keyboard) but doesn't chime. I'm starting to suspect the Delta PSU but not sure how to properly check it. Measuring 5.01V and 11.85V on the HDD power supply connector but I am unsure how to check the other voltage (-12V) and if it's strictly needed for booting these boards?
Both boards worked in the past. But stopped working quite close in time, both tested in the same machine using the same psu.

The Performa 600 board looked pristine and the IIvi had definite leakage.

For the record I managed to recap a dead color classic and revive it (my first) so I'm quite new to this.

Any advice is greatly appreciated!

Have you recapped the Delta power supply? I have had two, and they both had leaking capacitors. Note: They're not fun to re-cap.

Measuring the voltages of these power supplies is a pain, as they plug directly into the logic board. I've done it before by putting the power supply on it's side so that the logic board is standing vertically, but this requires careful maneuvering so as not to knock the logic board over. But that lets you measure the voltages from the underside.

However, my preferred solution is to use a known good power supply for debugging, and that sometimes involves using an ATX power supply using the following adapter: https://github.com/GeorgeRudolf/OldMacATX

This adapter converts the pinout from ATX to the 10-pin power connector and inverts the Power On signal for proper operation of the soft power circuit.

That being said, the "no chime" symptom of your Performa 600 sounds like a IIci board that I repaired where there was a broken trace under one of the audio capacitors. I wasn't getting a chime, or any audio out of the internal speaker, but I was getting sound out of the headphone jack. You might want to plug a set of headphones in to see if you have no audio at all - I think many Macs have a switch in the headphone/speaker jack to disable the internal speaker, and the audio signal routes back to the internal speaker through the switch. In my IIci's case, the broken trace was the signal from the switch back to the internal speaker.

The IIvi will need to be re-capped. There's possibly damage in the soft power circuit that is preventing the soft power circuit from powering on, or it may just need recapped and a through cleaning of the electrolyte. I should note that while I've successfully recapped a Performa 600 and a IIvi, I also have another IIvi board that appears to be dead after a recap and clean, and I don't see any trace damage to explain the lack of signs of life.

I hope this helps.

 

[chbi]

Have you recapped the Delta power supply? I have had two, and they both had leaking capacitors. Note: They're not fun to re-cap.

Measuring the voltages of these power supplies is a pain, as they plug directly into the logic board. I've done it before by putting the power supply on it's side so that the logic board is standing vertically, but this requires careful maneuvering so as not to knock the logic board over. But that lets you measure the voltages from the underside.

However, my preferred solution is to use a known good power supply for debugging, and that sometimes involves using an ATX power supply using the following adapter: https://github.com/GeorgeRudolf/OldMacATX

This adapter converts the pinout from ATX to the 10-pin power connector and inverts the Power On signal for proper operation of the soft power circuit.

That being said, the "no chime" symptom of your Performa 600 sounds like a IIci board that I repaired where there was a broken trace under one of the audio capacitors. I wasn't getting a chime, or any audio out of the internal speaker, but I was getting sound out of the headphone jack. You might want to plug a set of headphones in to see if you have no audio at all - I think many Macs have a switch in the headphone/speaker jack to disable the internal speaker, and the audio signal routes back to the internal speaker through the switch. In my IIci's case, the broken trace was the signal from the switch back to the internal speaker.

The IIvi will need to be re-capped. There's possibly damage in the soft power circuit that is preventing the soft power circuit from powering on, or it may just need recapped and a through cleaning of the electrolyte. I should note that while I've successfully recapped a Performa 600 and a IIvi, I also have another IIvi board that appears to be dead after a recap and clean, and I don't see any trace damage to explain the lack of signs of life.

I hope this helps.

Thank you for taking the time to respond! Both boards actually looked really clean after cap removal and cleaning. The IIvi is the board currently on the desk and basically all caps had leaked except the two cylindrical filter caps close to the PSU connector. The Performa 600 board looked really clean as well and had no signs of leakage at all but it's entirely possible I damaged it when I removed the caps...

Sounds like I need to inspect the Delta PSU closer, at a first glance it looked fine with no obvious leakage. I've looked at those PicoPSUs on Amazon with a ATX4VC to get a known good power supply setup since I haven't found a seller of those OldMacATX boards here in Europe and I'm currently not confident enough to buy a PCB etc to build one myself

I'll also test the headphones trick and see if there is any sign of 'intelligent' life on the Performa 600 board, otherwise I may just put it away for the moment and focus on the IIvi.