x68000 original restoration -- wow this thing has problems! SUCCESS!

[leonk]

--- PLEASE SCROLL TO THE BOTTOM FOR MY CURRENT STATUS OF THE RESTORATION ----

In the process of restoring an original grey x68000. It doesn't have the tetris psu but rather the rectangular one that sits where a hard drive would normally be found.

As I remove caps, I test them on my ESR meter. So far, no bad caps on main pcb.

But PSU had 2 caps that bulged and 1 that looked good but tested bad. I'm looking for zener diodes / zd31 but so far nothing! Just diodes on the pcb! could it be? no zener diodes in the original PSU?? What do people suggest I replace outside of the caps?

oh. and yes, the ni cad battery was bad.

[leonk]

did full cap job. psu dead. Not worth messing around with these death traps. Instead, I will install an itx 1u power supply.

Anyone tried the ngate mosfet instead of 74LS04 + resistor?

What do people recommend to do with fans? remove the fan from psu and just use original? or run both back to back?

[vanpeebles]

Is the fan just for the PSU or does effect the case temps too? Mine has the 74LS04 and resistor fitted. Seems to work well enough *touch wood*

[leonk]

Not sure case needs any cooling.. all the processors are exposed and don't even have heatsinks.  The stock fan is probably just for PSU as the PSU doesn't have one.

But if people fit modern ATX PSU's inside X68000, do they remove the fan from the ATX and use the old x68000 fan where it is, or do they have both fans running at the same time!?

[samaron]

My X68000 doesn't have a fan (picoPSU replacement). None of the other components in the computer develop enough heat to make a fan necessary. So the stock fan is only for the PSU. Either way, it is probably a good idea to replace it with something new which runs more quiet. Old fans tend to be noisy. Not sure what is common practice with these computers, but I would replace the fan if it is noisy.

[leonk]

how do you supply 12V to the pick PSU?

[samaron]

It has a power brick (or "laptop adapter") that supply 12 volt. It barely develop any heat as well.

[wbo]

My X68000 doesn't have a fan (picoPSU replacement). None of the other components in the computer develop enough heat to make a fan necessary. So the stock fan is only for the PSU. Either way, it is probably a good idea to replace it with something new which runs more quiet. Old fans tend to be noisy. Not sure what is common practice with these computers, but I would replace the fan if it is noisy.

Beware that while the picoPSU is quite efficient the manual does recommend using it with a fan if possible - especially if the PSU is being loaded anywhere close to it's rating.  If you are using a 120 or 160 watt pico PSU you are probably OK without one but if you are using the smaller 80 watt version it would be a good idea to leave the fan in to ensure that he PSU stays cool.

In my ACE HD I replaced the original fan with a nice quiet Noctua fan and put the Pico PSU inside the housing for the original PSU.  The result is a nearly silent system with enough air flow to keep my 80W Pico PSU cool under load.  I have tried running it without the fan and found the Pico PSU did indeed get quite hot when the system had be running for a long period of time.  With the fan, the Pico just gets slightly warm.

[vanpeebles]

That sounds like an excellent mod, do you have any pics of it wbo?

[samaron]

Don't worry, wbo. It is 160 watt I believe it was. As mentioned, barely any heat from it when I tested. Nothing close to needing a fan. I'm sure there are other components in the computer that get hotter.

[leonk]

I've been debating between picoPSU and a micro ATX (Flex ATX) power supply.

Flex ATX
- full ATX power supply
- just feed 110V to it using existing wire/fuse!
- No case mod (where do you pick up ground?? Original is just hot/neutral)
- ISSUE: Got 2 fans - blowing into one another - one from the case another from the PSU
- ISSUE: If you got Tetris style PSU, need a bit more work to get it to fit - will lose internal SCSI support (Not a big issue if you use external SCSI)

microPSU
- smallest ATX style PSU
- runs cool - case fan would be sufficient to cool it
- can still use internal SCSI
- ISSUE: Most use 12V DC/DC for source power.  Will need to modify case to feed 12V in using barrel plug
- ISSUE: What source DC PSU does one use?  Watts = volts * amps.  So for 160W micoPSU, one needs a 14A 12V external power supply.  That is A LOT of current, and very expensive power supply!  Most of the sub-$50 PSU's are 3-5A.  But at 5A, the most power you can get is 60W and that's with the power supply running at full load (not good).

Thoughts?

[vanpeebles]

Can you not gut the original PSU and fit the pico inside it, then fit the barrel connector where the PSU 3 pin socket would of been?

[leonk]

Can you not gut the original PSU and fit the pico inside it, then fit the barrel connector where the PSU 3 pin socket would of been?

Yes I can, and that was the original plan, but I'm still struggling with the original problem.. the required current @ 12V is close to 13 amps for 160W PSU.  That's A LOT of juice! 

Put it this way, the higher the voltage, the lower the current, the more efficient the circuit, the thinner the wires can be.  That is why data centers are 220V or even 440V in USA; and long distance transmission lines from power station increase the voltage to >200 kV!

These microPSU's do the exact opposite!  They reduce the voltage from 110V to 12V, requiring the current (amps) to significantly increase to maintain the same power (Watts).  You need to have thicker wires, etc to transmit 13A of current max.   I believe these microPSU's were created to be used by computers being installed in cars, where that kind of current can be provided by the car.  Not sure it makes sense for home use.

Thoughts?

[vanpeebles]

I thought they just use a laptop style powerbrick? Something like this?

https://www.amazon.co.uk/LEICKE-Charger-Routers-Displays-Monitor/dp/B00YXXAG7C/ref=sr_1_2?ie=UTF8&qid=1511254108&sr=8-2&keywords=pico+psu&dpID=415YENDaeWL&preST=_SY300_QL70_&dpSrc=srch

with a pico 120w on the end of it?

[wbo]

The pico PSUs are designed to use high current 12V power bricks similar to those used for some laptops.  Mini-box sells several high quality 12V power bricks suitable for use with the pico PSU in the USA and Amazon has quite a few as well.  These types of power supplies are very common for various thin clients, digital signage PCs, and other small low-power PCs so they really are quite common.

If you use a 160W pico PSU you don't necessary need a 12V supply that is capable of 160W of power.  The x68000 will never draw that much current - the 160W is just the maximum the pico is rated for  If you power it with a lower wattage supply then the real limit will be the power supply you use.

A 120W power brick should be plenty and a 90W brick would probably be fine as well.  I believe the original PSU may have been rated for 70 Watts or so and there is some loss due to the DC-DC conversion in the pico but since it is >95% efficient a 90W supply should still be plenty.

I don't know where you live but a power supply like the one vanpeebles linked to should work just fine.

[leonk]

Great.. thanks for the link.

FWIW, not a fan of running electronics at their limits.  I've seen enough china-made "good" switching AC/DC bricks toast by running close to limits.  If the computer on average uses 60-90W, then you should be using 150W PSU with 150W AC/DC adapter.  Running a 90W PSU at limit will drastically reduce its efficiency and increase likelihood of total failure.

[vanpeebles]

I'm sure the original PSU says something like 90w MAX

[leonk]

So the X68000 is "alive" but nothing happens.  I press the power button, POWER goes GREEN, but HIGH RESO turns red as well (what is that?)  I did replace the SRAM battery.  Anything I can press on keyboard to force POST?

[leonk]

OK.  Found some more interesting "things":

1) When powering off the ATX PSU, the 5V line to the control board drops to 4.5V.  The 5V vsb is at 5.01 and 12V is at 12V
2) I removed the 69.55199mhz crystal and the system behaves the same way! (I don't have a replacement crystal - so I might be at the end of this journey) 
3) When I put the crystal back, as well as removed and cleaned the 74132 next to the battery .. the system now goes directly to power on / high reso.  No video output, no keyboard life .. doesn't listen to the power button.  Pulling 5V (while leaving the rest in play) is the only thing that brings it back to "standby" mode.

Argggg...  Suggestions?

[vanpeebles]

Do you have the mod fitted with the 74LS04?

[kamiboy]

I had a OG grey with similar symptoms. Turned out the 69 mhz crystal was dead, I replaced it and it came back to life. Unfortunately the power on/off wasn't functioning so while diagnosing that I somehow managed to kill the machine permanently. I gave up on it in the end.

[leonk]

sorry to hear that. It seems that these machines are very sensitive and when things fail, it's a cascade effect. If you have a good crystal to sell, let me know (I'm in Toronto)

The system has been retrofitted with the 74LS04 chip. Initially, on plugging the atx psu in, just the red power light was on / ATX off. I would press the soft power button and ATX will turn on, power go green and high reso (high resolution output?) will go red. Pressing the power button would cause the power led to go off, high real stay on and atx never turn off!! Only unplugging atx did a proper recycle.

I removed the crystal and 74132 next to new battery (I installed battery holder + ML2032) Cleaned the pads and soldered back in.

Now on ATX plugin the system goes directly to power green, high reso. soft power button has no effect.

I truly believe that the problem is with the 5V rail. For it to drop to 4.5V means something is pulling it down hard. I can't imagine 5V devices able to work in 4.5V

The x68000 is a complex beast. lots of ICs across many boards. And if you got only 1 with no good working one for comparison. It's an almost impossible task.

Luckily I only have about $300 into it. But I would really like a working x680000. 

[JulBS0]

Hi,

The soft power malfunction may be caused by a dead 69MHz oscillator (it was the case on my original X68k).
The power on/off signal that goes to the PSU is driven by the system controller and the MFP, which are themselves driven by the CPU.

Somewhere (probably very early) in the BIOS, the system tries to talk to the video chips, but since they don't have their clock signal, they don't respond, and the system hangs.
And the "power off from front switch" signal is actually an interrupt sent to the CPU by the MFP, but the interrupt handler seems to be set up after the video check.

You should try to change the oscillator. Finding the same exact part seems to be impossible (on another thread, a forum member which I've forgot the name said he contacted the manufacturer, and they don't make them anymore).
However, programmable oscillators do exists and, provided you can grab a TTL one, it should work like a charm.

I purchased mine from Cardinal Components pre-programmed through Digikey, and after battling a bit to remove the old oscillator and isolate a pin, the machine came back to life.
As you live in Canada, shipping shouldn't be excessive, at least I hope so.


About your 0.5V drop on the main 5V line, the machine *should* work. Mine does at least on a cheap no-name PSU.

[leonk]

Thanks.  I have a few questions for you that you might be able to help me with.

1) Can you tell me what the exact part number is that you ordered from Digikey?  There's so many options.
2) I have ability to cleanly remove components with my desolder station.  Are you able to provide instructions on how you wired the crystal? Current I believe is 2 GND points and 2 outputs.
3) What voltage are you getting on 5V rail?  I'm seeing 4.5V everywhere (eg Vcc and GND on the 2 BIOS EPROMs).

P.S. THANK YOU! I can't believe Digikey is programming Oscillators.  THIS IS AMAZING!

[JulBS0]

The oscillator I used can be found under the CPPT1-HT0PT-ND reference on Digikey.
It has the good size (DIP-14 footprint) and the right pinout, except for a positive Output Enable signal on pin 1.
That pin is grounded on the X68k motherboard, so you will have to isolate it.

In my case, due to the lack of adequate tools, I butchered a bit the motherboard (not proud of it) in order to prevent the pin to touch the borders of the pin 1 hole, and it works thanks to the internal pull-up of this Output Enable pin.

It should be possible to make something less ugly, maybe with a DIP-14 socket or a little piece of stripboard.
Since the frequency is rather high, the later option might not be advisable. If someone with a proper electronics knowledge read these lines, feel free to comment.

As for the voltage, I currently don't have access to my X68k stuff, but I remember that the 5V line voltage was around 4.5-4.6V, with both floppy drives plugged and a CZ-6BE1 memory extension. The computer works, without any suspicious behavior.

[leonk]

Thank you for all your info.  I knew that 2 pins were ground, but wasn't sure about the other 2 (if they were flipped or direct insertion).

As for pin 1 (option pin), can't one just cut it and use electrical tape over the hole?  It's not like we have the means to reprogram these oscillators.  According to digikey, they can only be reprogrammed twice anyways. 

[JulBS0]

Well, yes, it should work.
The internal pull-up is rather weak, but since we leave the pin unconnected, it should not be a problem.

I wonder why I didn't think about it when I installed the oscillator in my X68k... (maybe it's the "hacking vintage hardware at 3 A.M." effect)

[leonk]

When the SRAM battery leaks, that stuff is destructive!  It seems that the OG X68000 has a major design flaw - the oscillator is right next to the SRAM battery!

Thank you JulBS0 for the Digi-key part number.  Here's what I did:

- I removed the 3 closest IC's to the battery.  I noticed the legs on them were really badly corroded. 
- 74132 - added 14 pin socket and replacement part:  TC74HC132APF-ND (NAND 4CH)
- little 8 pin IC next to battery is low 5V sensor!  It triggers reset when 5V is too low.  Modern part number 296-1801-5-ND
  It's called an IC 4.55V SUPPLY MONITOR 8-DIP
- I cut pin 1 from the oscillator, put electrical tape on pin 1, and solder it in place
- The remaining resistor/diodes that were corroded had the solder sucked out, and fresh solder placed.  Good ISO alcohol wash to rid of any contamination.

Now, the original PSU exploded!  So I made the ATX adapter cable.  I noticed a problem last time (more on it shortly) but now I'm able to start and shutdown the x68000 using the soft button!!  I even tested both floppy drives (after cap kit) and they work great!!

My initial plan was to have everything run off the ATX molex.  Bad idea.  The 5V rail there doesn't have enough current to properly start the x68000.  The HIRESO LED never turns on.  If I cut the 5V wire and push it into the big IDE power molex (red to red) then the system starts just fine.

Time to purchase one of those 1U small ATX PSU's, the CF2SCSI and complete this project. 

If you guys want more pictures, I posted it all on twitter.  My handle is leonkiriliuk

https://twitter.com/leonkiriliuk?lang=en

[vanpeebles]

Excellent work! I bet you hit the roof when it fired up working