My 512k Build... "FLUP FLUP FLUP"

[iMac600]

I finally got around to tearing down the old Macintosh 512k to see what the problem is. Visually the electronics appeared fine, so it looks like I need your help, 68kMLA.

It has the documented "FLUP FLUP FLUP" noise (the floppy drive sound) when it tries to power up. It's like it's in a constant loop of powering up and powering down and the FDD spinning up over and over, creating the flup noise, confirms this theory. I heard from somewhere that this may be a fail-safe, but i'm not sure.

Larry Pina's book advised that I suspect 7 capacitors on the International logic board (C3, C24, C27, C28, C30, C31 and C32 respectively) and also turn the voltage pot down in case someone has set it too high. I have replaced those 7 capacitors and adjusted the voltage pot accordingly to no avail, the system is still Flup, Flup, Flupping away.

Next on the checklist is to visually inspect and replace the 3 rectifiers. Please also take note that the machine still appears to power cycle even with the logic board disconnected (no idea if this is normal or not) and there is no battery currently fitted in this thing.

However i'm not entirely sure I should be focusing on these rectifiers just yet. The CRT didn't need to be discharged at all, indicating not even the tube is receiving the necessary kick to turn it over. It has started a few times before to a full picture (a Sad Mac) so I know it's perfectly capable of working. Now it's not even getting a charge.

On the board are 4 200v 100uF capacitors, not documented in Larry Pina's book, which I can only assume filter the charge coming into the system from the mains. Being 200v (and AU power being 240v) makes this scenario quite likely. If the CRT isn't getting any charge, and the logic board is struggling to power up, then maybe I should instead turn my attention to these 4 capacitors next.

They aren't cheap, at around $10 a capacitor. I need 4 of them, so i'd need to sink $40 into these, otherwise i'd have bought them and tried them already.

Should I have a strong reason to suspect these 4 capacitors? If both the CRT and the logic board are struggling, then perhaps I should examine the analog board further up the line and start by removing/replacing these mains capacitors.

Does that sound logical, or am I just wasting my time?

If anyone has any further knowledge of these old systems and the Flupping issue, i'd love to hear your suggestions to get it ticking again.

Thanks

- MB

 

[iMac600]

Also note, with the CRT disconnected, it "flups" much faster, but still doesn't power up. I think this isolates the issue to the analog board.

 

[phreakout]

iMac600,

This sounds to me like the power supply is the problem. When you take the CRT out of the work load, the "FLUP" sound was much faster, which tells me to check for proper voltage going out of the power supply unit. Is the display completely dark when the 512k is put back together? Or does the screen show a slight blip of light, a small dot of light in the center, or a horizontal line? Maybe a capacitor is bad somewhere on the PSU.

Give that a try and report back with what you find.

73s de Phreakout.

 

[iMac600]

This sounds to me like the power supply is the problem. When you take the CRT out of the work load, the "FLUP" sound was much faster, which tells me to check for proper voltage going out of the power supply unit. Is the display completely dark when the 512k is put back together? Or does the screen show a slight blip of light, a small dot of light in the center, or a horizontal line? Maybe a capacitor is bad somewhere on the PSU.

It used to. Now it no longer does.

I'm thinking that perhaps i'll replace the remaining electrolytics. I'll also get some quotes for the large 200 Volt electrolytics that are likely to be causing significant problems for the system, including the issues reported here.

What makes me think a little is that the machine has started before, after the flupping issue began. After working, including power cycles for about 6 hours, it started flupping again and displaying a small white dot in the center of the display. Now it won't start at all. This gives me the impression the power supply is deteriorating, hence suspecting the large 200v mains supply capacitors.

So... where to from here? Swap out every last capacitor on the analog board, it seems, then pray for a miracle and hope this old warhorse powers up. If it still doesn't go, then the rectifiers are the next step.

Thankfully i'll probably make a run to the supplier again this afternoon, so it could be less than 24 hours before we have a successful boot.

I'd love to see this little machine work again. It's become my favourite of the 68k's over the last month or so.

 

[Scott Baret]

If you're not comfortable with capacitor swapping, find a good working platinum Mac Plus analog board (if it's pulled from the machine you can tell what color machine it was from by looking at the power switch). The platinum Pluses have sturdier analog boards than any beige pre-ADB machine from my experience.

And yes, the "flupping" noise is a common problem on the early Macs when the analog board fails. In fact, I recall reading a book (Upgrading and Repairing Macs) that used that exact word when describing the noise made by those computers.

 

[iMac600]

Well crew, I replaced 7 suspected capacitors (as per Larry Pina's book) last night, but not the High Voltage 200v capacitors.

Today, I have purchased said capacitors and will tackle the job tonight. We can hope that the Mac will power up after this. I've also secured a hot melt glue gun to reapply the melted glue I had to remove from the old capacitors. The glue gun was free, but the capacitors cost me $36 AU for just 4 of them, so i'm praying here that this will resolve the problem. I blew my last cash reserves on these things, but I couldn't resist the chance to have it working again.

Fingers crossed.

 

[equill]

The term 'flupping' was originally coined as a specific appellation for a specific diode-related fault in the PAB of early Macintosh models, a fault that may precipitate capacitor failure, perhaps, but is not the primal cause of the problem. Some of what you described above is much more like 'flopping'—for the sake of a descriptor—than flupping. However, tomlee59, in his paylife alter ego, some time ago posted some avenues of approach to a problem with some kinship to yours. If you also look for the schematics and narrative that tomlee59 has lodged here and elswhere for the same Macs, you should be able to check the PAB with some certainty of outcome. You are the man on the spot (in both senses), so you will be able to apply that info. with a good chance of a successful outcome. Good luck.

de

 

[Mac128]

It has the documented "FLUP FLUP FLUP" noise (the floppy drive sound) when it tries to power up. It's like it's in a constant loop of powering up and powering down and the FDD spinning up over and over, creating the flup noise, confirms this theory.

This throws me a bit ... are you saying the FDD continually spins up and down? But if you remove the logic board, how can the sound continue if the FDD is no longer connected?

If you have the Pina book, then you have all the information available on the Flup assuming it's not multiple problems and you are diagnosing it correctly. I would do exactly as you are and go through each one step by step.

 

[iMac600]

This throws me a bit ... are you saying the FDD continually spins up and down? But if you remove the logic board, how can the sound continue if the FDD is no longer connected?
If you have the Pina book, then you have all the information available on the Flup assuming it's not multiple problems and you are diagnosing it correctly. I would do exactly as you are and go through each one step by step.

The CRT makes a whistle in time with the FDD. The whistle continues even when the drive is disconnected.

I don't have the Pina book, just a few pages scanned from it.

I've replaced the 200v HV capacitors and there's still no change. I've spent $70 AU on this thing now for no result, so I think it's time to give it up and let it die.

EDIT: We have power. The flupping is gone and the CRT is now getting a charge (it sparks when I discharge it). However there's still no video and no chime. Getting closer though, maybe a few more flows of the analog board will have it working.

EDIT 2: Sad Mac Baby! Time to get to work on the logic board. Unfortunately the code below the Sad Mac is garbled, so I can't read off what the error is.

 

[iMac600]

Analog board checks out, so my repair there was a success. Unfortunately the logic board is toast... me and Wackymacs on IRC, with his copy of Larry Pina's book handy, were unable to determine the cause of the "Sad Mac" as it had no hex code listed below it... just garbage print. Unfortunately it's beginning to look like one of the IC's could be to blame, unless capacitors could also cause this issue (i've replaced 2 out of 3, ran out of the last one).

So... looks like i'll be in the market for a 512k logic board then! Doesn't need to be a 512Ke board or anything... I can provide the ROMs and the 800k drive for it, I just need the board itself. I'll see what I can come up with anyway.

 

[macgeek417]

 

[Mac128]

were unable to determine the cause of the "Sad Mac" as it had no hex code listed below it... just garbage print.

There are a number of known issues that can cause a sad Mac. The garbage component suggests multiple problems. But let's assume the most basic.

Any number of the RAM chips could be bad. Not knowing the exact ones at fault would make for a painstaking replacement.

I presume you have adjusted the analogue voltages back to optimal after your repairs? That is a common cause of the sad Mac. Also, remove the programmer's switch if installed.

 

[iMac600]

I presume you have adjusted the analogue voltages back to optimal after your repairs? That is a common cause of the sad Mac. Also, remove the programmer's switch if installed.

Good point there is that the voltages could be out of whack. I haven't adjusted them for optimal, as a matter of fact I reset them to what they were when I received the system, but only visually... i'm still not sure what "optimal" is. If I can get some documents describing the optimal settings for these, i'll be sure to give them a shot. Apple's service source documents show how to perform the adjustments, and the figures they should read at, but unfortunately they require one of Apple's internal test tools.

I wouldn't be surprised if the board was dead however... the ports on the back look pretty shabby.

I may be able to secure another logic board anyway, should I need it.

 

[iMac600]

I've reflowed every joint on that board (literally, all 2000+ joints), just in case. Still getting a Sad Mac error unfortunately. I'm not having much faith in the future of this logic board.

 

[Mac128]

If I can get some documents describing the optimal settings for these, i'll be sure to give them a shot. Apple's service source documents show how to perform the adjustments, and the figures they should read at, but unfortunately they require one of Apple's internal test tools.

All you need is a multimeter and test pin 6 on the power supply to adjust to +5V. See Tom Lee's documentation for proper adjustment voltages/proceedures.

Not sure why you reflowed all 2,000+ joints. That is rarely a cause of the sad Mac since they are unlikely to crack under use the way many may on the analogue board. The most common failure on the logic board is bad RAM chips, mismatched/align ROMs, and low voltage.

 

[tomlee59]

I've reflowed every joint on that board (literally, all 2000+ joints), just in case. Still getting a Sad Mac error unfortunately. I'm not having much faith in the future of this logic board.

That's a lot of work (and probably unnecessary).

If you haven't already read the lone pdf document at http://68kmla.org/files, you might want to. In particular, check out the section on the "whup-whup-whup" sound, which might be the same as your "flup-flup-flup."

Note for future troubleshooting: Take some basic measurements very early on in the process. Soldering 2000 joints should be far, far down on the list of things to try (a bit after "transplant spleen").

 

[Osgeld]

heh a good reason to own a goodwill toaster oven, but yes last on the list

 

[iMac600]

Not sure why you reflowed all 2,000+ joints.

False hope and I needed something to take my mind off things for a few hours.