x68000 (CZ-600C) power supply removal? Trick? Tips?

[Arcade]

Howdy everyone-- new to the scene, just got my giant box of x68K's so I've been pulling things apart to repair battery leak damage and recap things.

On the original model x68000 (CZ-600C) with the 'rectangular' shaped power supply, is there some trick to removing it from the case?  I extracted all the obvious large screws that go through the metal tabs and in to the plastic (I think there were four or five) as well as a little bracket that connected to the floppies, but even after that it still feels like it was somehow attached in the center?

Is there some kind of sliding latch or another hidden screw somewhere else?  I was tempted to BFFI it, but didn't want to risk breaking the plastics...

Thanks!

[Segasonicfan]

I made a video on how to remove the PRO model PSU on youtube, might be pretty similar.  Do you have a pic of it?

out of curiosity, how many broken X68ks did you get?

[Arcade]

I was watching that earlier today! The CZ-600C power supply is kinda similar to the original supply in the Pro, but maybe not exactly the same?  As soon as my tablet gets enough of a charge that Dropbox will let me upload photos I'll post a couple pics of the power supply section.

I picked up a total of nine machines (assortment of original, Ace, Expert, Expert II, Super, XVI and a couple duplicates).  I'm going to work on new I/O cards and purpose made CF converters and wanted a selection of models for compatibility testing.  It sounded like one machine was probably working (the XVI), the others were 'junk' and likely untested or dead.  (As a friend of mine says-- "anything worth doing is worth overdoing".) ;-)

[Arcade]

Here's the pictures and I marked the five screws I removed... It still seems like it's somehow connected in the center, but I don't see any other fasteners or a way to remove the top cover of the PSU in situ.





(I also removed a little bracket that attaches to the floppy drive frame as well-- it's connected to the right-most screw in the first photo.)

I'm usually pretty good at getting in to things, but this one has me kinda stumped...

[BlueBMW]

I believe there is a screw that holds the power supply in that originates in the other tower.  Why they put a screw that way.... Who knows.

[Arcade]

I believe there is a screw that holds the power supply in that originates in the other tower.  Why they put a screw that way.... Who knows.

That would explain it! ...and that's what it *feels* like.  I was really trying to avoid having to take that other side apart. ;-)  Sharp certainly didn't pull any punches when it came to the screw budget on these!

Thanks, I'll see if I can dig in from the other side...

[H68k]

Trying to get the motherboard tray out of it's tower is only one of the few annoying things of working on the tower models thankfully. (compared to trying to work on a compact model.. those are about as fun as it is trying to get one of the current gen PS4's or Xbone's apart!)

There's a peace of steel with hooks that runs up the backside of the plastic, you have to push the tray forward to get it off the hooks and then lift it out.. trying not to get one of the hooks caught in the tray's slits again. you then should be able to lift out the motherboard tray, providing all screws holding it in place and cables have been disconnected.

[Arcade]

Heheh... Yes, I avoided the compact for that very fear.  It reminded me too much of a Casio LCD projector I had to poke around inside a while back.  Nightmare! ;-)  I'll probably be a day or so before I get time to poke at the 600C again, but thanks for the info!

[Arcade]

So, for future reference-- yes, you need to remove the motherboard from the opposite side of the tower in order to get at a small metal bracket that is screwed in to the back side of the power supply on the CZ-600C before you can remove the PSU.

[H68k]

Interesting.. I guess they removed it from the ACE model onwards, and went to the notorious ticking time bomb that is the shrunken "tetris" block power supply to make way for the hard drive mounting bracket, as they started offering pre fitted hard disk's as an option.

[eidis]

 Hi H68k !

To be completely honest, the tetris power supply is not that bad. If it dies, it does not take anything with it and to be completely honest, every PSU is a ticking time bomb because of the capacitors. 20 years of service is way more than they were intended to be used for.

Keep the scene alive !
Eidis

[H68k]

Hmm... When my XVI tower started having some issues. I first thought it could be a power supply related one.. (I sort of did some research into the bussiness of X68k power supplies before hand, but not in any real depth)

when I really started researching in depth to X68k power supplies. I started reading about the horror story's on Japanese X68k fan sites and user blogs, about how there where supposedly unreliable and quite prone to failure.. and sometimes with quite spectacular results. such as: killing the motherboard or the IO board or the FDD logic boards etc.

You could make the tetris block PSU reliable.. but from what I read, I was under the impression that you had to pretty much rebuild almost the entire PSU to do so. witch lead me to the conclusion (like everyone else in said situation) that the best and easiest thing to do, was the replace the original power supply (witch I'd dubbed, the ticking time bomb) with a much more reliable ATX power supply mod.

As your more "in the know" than I am on X68k hardware issues. I guess the tetris block PSUs are not that bad as they've been made out to be then?

I've seen quite a few computers be killed though, all because of cheap or badly made PSUs (one was responsible for the death of my beloved Abit NF7 motherboard of what used to be my trusty, long serving Athlon XP rig from years ago) in my previous line of work..

[eidis]

 Hi H68k !

Don't remember by heart but somewhere I read that the X68000 PSUs used capacitors which were in the borderline of voltage which they needed to filter. We all know that larger voltage tolerance in capacitor specs means more life so that could be one contributor to their failures. Usually a computer gives very noticeable early warnings when there is a problem with power supply. Most often strange unexplainable failures appear, like it does not work reliably in the first 15 - 30 minutes but then all is fine. There is simply no way around it. We must replace capacitors in every PSU of our 80's and soon 90's systems or risk damaging them. There is a thing called "crowbar protection" which can be implemented in the older 8bit machine PSUs. It protects against overvoltage. However, just to be on the safe side, an overcurrent protection is needed as-well. IMHO the easiest way to achieve this is by replacing the voltage regulator with a model which supports this.

Keep the scene alive !
Eidis

[Arcade]

I've torn in to a couple of the 'tetris' block supplies now and all in all they didn't look like a terrible design to me.  They actually have good quality caps (both I've checked so far have had Elna 105C long-life caps, so they weren't skimping on parts cost at least) and there was no tell-tale signs of component stress-- resistors aren't discolored, the PCB doesn't have any discolored spots from heat build up, etc.

Having said that, virtually every last electrolytic cap in them was leaking.  (That's *not* typical.)  Maybe it was just a weakness in the manufacturing process or materials, or maybe the interior temp was just too high for too long.  They did use some 'dry' thermal washers on the larger TO-247 packaged parts (I didn't look, but I assume they're either FETs or diodes for the switchers) which probably isn't great for maximum heat transfer, but they didn't look like they got particularly toasty so it's probably fine. 

I'm rebuilding the old supplies with some modern caps-- the upside is that since electrolytic cap tech has advanced over the years it's easier to get higher voltage/higher value caps in the same or smaller packages now.  Smaller caps will allow for better air flow and cooling.  I'll run some tests once I have a machine working and bust out the thermal camera and see if anything really gets dangerously hot or not.  I strongly suspect that a 'modern' gaming setup (ie, CF card and minimal floppy disk access) will help keep power use down (reducing stress on the PSU).  It *is* really tempting to do something about the massive numbers of DRAMs on the original motherboards.  Those soak up power like crazy.  You could probably shave 10-20W off the power use by switching to higher density DRAM.  (Although that's a lot of desoldering of IC's.)

[eidis]

 Hi Arcade !

I noticed the following things while refurbishing a 'tetris' block PSU. It had quality Nippon chemi-con capacitors. The original fan was very loud and did not cool the system efficiently because its blades are very small. It was replaced with a modern one and modded to use 5v instead of 12v because the system did not have original hard drive and used CF. The result was better airflow and very quiet machine.

Keep the scene alive !
Eidis

[a24tanabe]

I'm sorry about not following this thread completely (because of being short in English).
About to tetris PSU, it's most problem is containing caps using quaternary salts as electrolyte.
They were thought long life and good performance (low ESR and so on).
But about 10 years later it was found that they leak electrolyte and cause short and break PSU.
So it is needed replacing all caps and cleaining leaked electrolyte completely.
If not ,PSU is broken again by remaining electrolyte.