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Sun 2/120 power supply

pkhoury

pkhoury

Experienced Member
Joined
Dec 6, 2007
Messages
300
Location
Bandera, TX
Does anyone here have a Sun 2/120? I'm in the process of recapping the Boschert XL750 power supply, as the last time I powered on, it started smoking, and there is definitely evidence of some caps having leaked. I opted to replace ALL tantalums and electrolytics, including the screw mount capacitors, as these are now all forty years old. The filter caps look okay, but the two screw caps on the +V side both leaked some, or at least one leaked and bulged a little.

Primarily my question - I forgot to take a photo of the board before I disassembled it and have a red wire with a ring terminal. I think I know where it goes, but a photo of the same supply (which is really a crapshoot) with the cover off would be helpful. I know where everything else goes, though.
 
Is this what you're looking for?
 

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Yes, thanks! I figured that red wire went where it goes, but I just wanted to make sure.

Now I'm just hoping FedEx gets my package to me tomorrow so I can finish rebuilding the Boschert, then see if the board powers up without recapping that. I'm on the fence about bringing a bunch of Suns to VCF SW in June (was originally going to bring a bunch of restored 1990s ThinkPads).
 
I vote for bringing the Suns as they tend to be rare at festivals other than VCF West.
 
tokenalt said:
I vote for bringing the Suns as they tend to be rare at festivals other than VCF West.
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I might save the ThinkPads for another year, or just another local club meetup. I was honestly worried about people banging on the keyboards and whatnot. Whereas on a UNIX machine, I don't care if someone else uses it. For all the narrow SCSI machines, I'll be using ZuluSCSI anyways, so if someone hoses the file system, a backup is easy to restore.

Now if I really had the time, I'd add in my VAX 4000 VLC, an Alpha, PA-RISC, and RS/6000 to the mix.
 
This is my Sun display at VCF East 2.0 held at Sun's office in Burlington, Ma.

The left tower is a Sun 2/120, It has 1152x900 monochrome graphics, 5 MB RAM (4 MB on a Helios Memory Board), a Sun/Intel Ethernet board, a Sun Serial/SCSI adapter, a Xylogics 450 SMD controller, 2x CDC 94155-85 71 MB ESDI disks connected to an ESDI-SCSI Adaptec board, and a 20 MB Archive QIC tape drive. The right tower contains 2x Fujitsu M2322K, B03B-4745-B002A, 168 MB 8" SMD disks.

The workstation sitting on top of the server is a Sun 2/50 with 4 MB RAM, onboard Ethernet, 2x Serial and 1152x900 monochrome graphics, a 6Ux160 VME adapter board holding an additional 1 MB RAM and a Sun-2 SCSI controller. It was running as a diskless workstation at the VCF but it can also boot SunOS 4.0.3 from an external SCSI disk.

The tower at the far right is a Sun 386i/250.

Left Rear: Tadpole Ultrabook, Left Front Tadpole SPARCbook 2, Middle Left Sun Voyager, Middle Right, TRIgem/RDI Britelite LX, Right Tadpole SPARCbook 3GX, Far Right: Sun JAVAstation.
1714139676363.png
 
@m_thompson VERY NICE collection. I had a SPARCbook 3GX about 25 years ago, but it would reboot often with a watchdog reset. I remember selling it to buy a ThinkPad 760ED.
Jealous you have a SCSI controller in your 2/120. I wish I did, so I could at least boot up locally.

I don't suppose you'd happen to have a disk image of your install for SunOS 4.0.3 by chance, would you? Nice to also see a working ECL monitor. I don't even think I saw one of those working in the mid-90s, when my mentor first introduced me to Suns (he wanted to sell me a Symbolics, but I opted for the 2/120 and an IPC).
 
bear said:
Is this what you're looking for?
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Just out of curiosity, what did you replace those Mepco 26000uF caps with? I was only able to get some Cornell-Dubilier caps from Mouser (27000uF/15V), and they're maybe 1-2mm too high, thanks to the terminals themselves. It's a pretty tight squeeze as I'm getting everything back together, so I can then check voltages before hooking things up.
 
I did a really big boo boo. I forgot to trim three sets of leads on the 5V board for tantalums I replaced. The hard lesson of not ignoring my phone while working.
Anyway, the power supply does power up, but it's not putting out any voltage, and the 5V board in particular has 0.4 ohms between terminals. I'm trying to figure out how to diagnose it. Everything else has between 500 ohms and several K ohms.
 
pkhoury said:
Just out of curiosity, what did you replace those Mepco 26000uF caps with? I was only able to get some Cornell-Dubilier caps from Mouser (27000uF/15V), and they're maybe 1-2mm too high, thanks to the terminals themselves. It's a pretty tight squeeze as I'm getting everything back together, so I can then check voltages before hooking things up.
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A bodge. I couldn't find suitable direct replacements. If I could have found correctly-sized 27000uF units as an option, that's probably what I would have bought. As it was I still had to use a file to shave about 1-2mm off the screw terminals of the replacement part I used, to get it to fit.

Anyway it worked as a repair and the thing is still working 13 years later.
 

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bear said:
A bodge. I couldn't find suitable direct replacements. If I could have found correctly-sized 27000uF units as an option, that's probably what I would have bought. As it was I still had to use a file to shave about 1-2mm off the screw terminals of the replacement part I used, to get it to fit.

Anyway it worked as a repair and the thing is still working 13 years later.
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It looks like you're using the same Cornell Dubilier part that I used. I opted for two (since I already bought it). So just shave a little bit off the screw terminals to get it to fit? I just noticed your Cornell is 49000uF and 7.5V. Is it the same size as the original part? Or was I missing something? I thought both original Mepco caps were 26000uF @ 7.5V, unless the other was different. I ended up finding another Boschert XL750 on ebay that I snatched up, in case I screwed up something in this one I already rebuilt. That one at least puts out some voltage, albeit the other lines are seeing less than 5V.
 
pkhoury said:
It looks like you're using the same Cornell Dubilier part that I used. I opted for two (since I already bought it). So just shave a little bit off the screw terminals to get it to fit? I just noticed your Cornell is 49000uF and 7.5V. Is it the same size as the original part? Or was I missing something? I thought both original Mepco caps were 26000uF @ 7.5V, unless the other was different. I ended up finding another Boschert XL750 on ebay that I snatched up, in case I screwed up something in this one I already rebuilt. That one at least puts out some voltage, albeit the other lines are seeing less than 5V.
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Same size, apart from the slightly over-tall terminals. The 2x 26000uF are wired in parallel, which makes them equivalent to 1x 52000uF, with a pretty sloppy tolerance (-10% +75%). 49000uF is (just) within that tolerance, but to be "safe" I augmented it with a 4700uF part, effectively giving 53700uF. Well within original tolerance, even at the low side of the replacement parts' range(s).

You need a load on the PSU output or it won't regulate. I can't remember what I connected. Most of the time I just connect a faulty 3.5" SCSI HDD I keep around for such purposes (be careful to _not_ connect such a thing to the molex connector for the tape drive, which is +5/+24v instead of the normal +5/+12). Sometimes this isn't enough load on +5, if the PSU is designed to regulate off that rail instead of the +12. I also can't remember what this PSU specifically did with no/insufficient load --- I do remember I was very disappointed when I first put it back together, because I thought I'd made the thing worse. But no, it was fine, just needed a load. You might need to experiment some.

ps. I don't know about measuring resistance across a PSU output rail, but 0.4 ohm might not indicate any kind of a problem - there's a lot of amps coming out of that PSU on 5v.
 
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Thanks for the tips. So for me, I replaced both 26000uF caps with two 27000uF, so that's still fairly close, though both have the same sloppy tolerances again.

Good to know on putting a load on it. I have plenty of crap 3.5" SCSI drives. I guess I just need to find 2 or 3 that at least spin up, to generate some sort of load. I'm naturally hesitant to connect the multibus itself until I know it's getting the voltages that should be coming out of the supply.

You mentioned the tape drive needing +24. I noticed there's also a tap on the multibus planar for +24. What else is it used for? Also, there's a reference to -5 and -12. Does this PSU output -12 and -5, or are those connected in reverse on the PSU to achieve the negative voltage? I did a crappy picture with my phone to remember what went where.

Either way, at least I'll have a spare supply if all else fails. Believe it or not, I consider my 2/120 as one of the prize pieces in my collection, so I'm pretty eager to get it running (and show it off at VCF SW in June).
 
pkhoury said:
You mentioned the tape drive needing +24. I noticed there's also a tap on the multibus planar for +24. What else is it used for?
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Just the Archive Sidewinder, AFAIK. There are two Molex connectors with +5/+24 (IIRC? Maybe that was just in the Sun-2 SCSI shoebox. It's been a while since I've been inside the 2/120). The second is meant to power the Sysgen SC4000 tape controller (the SC4000 only connects to the +5 supply). Definitely don't plug it into the ACB4000 or the hard drive. The other set of molex connectors are +5/+12 for those devices.

If there's +24 on the Multibus, it must only be on one of the "reserved" pins on P2. It's not in the spec. I can't think of any reason any of the normal Sun cards would use +24 from P2.
 
bear said:
Just the Archive Sidewinder, AFAIK. There are two Molex connectors with +5/+24 (IIRC? Maybe that was just in the Sun-2 SCSI shoebox. It's been a while since I've been inside the 2/120). The second is meant to power the Sysgen SC4000 tape controller (the SC4000 only connects to the +5 supply). Definitely don't plug it into the ACB4000 or the hard drive. The other set of molex connectors are +5/+12 for those devices.

If there's +24 on the Multibus, it must only be on one of the "reserved" pins on P2. It's not in the spec. I can't think of any reason any of the normal Sun cards would use +24 from P2.
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No, I noticed last night, also late at night (when I usually work) that there are some Molex connectors with +24 on them. Sadly, I don't have a Multibus SCSI controller, so that's a moot point for me. It would be nice to stuff a 300MB Micropolis inside the machine, though I'd rather use a ZuluSCSI if I had such a controller. My back is already jacked up, so the lighter I can keep the computer, the better.

Yeah, I couldn't think of why +24 would be used, either.

Worst case scenario, if I can't get a working supply, do you think I could get away with independent Mean Well supplies for the power? They do make a 5V@100A, and the 12V is easy, but I'm not sure how to achieve negative voltage, though I saw a diagram online - something about getting another supply, connecting ground from one supply to positive on the other as reference, and then provide the negative voltage to the bus. I'd prefer to keep things original, but this system is a bitch to pick up with that overly heavy Boschert. Even the side panels weigh a lot.

More unrelated trivia - my system came from Los Alamos labs, and inside is a post-it saying "X-Div Property." I'll see if I can't get a picture of it later. The guy I bought it from told me it came from the nuclear design division, given it's maxed out at 7MB of RAM.
 
The normal Sun SCSI adapter and SunOS 2 itself has issues with SCSI devices with embedded SCSI...

If someone says they got a ZuluSCSI working, check how they did and restrictions. I dont believe SunOS 2 as such supports that ie embedded SCSI, it wants a ACB4000
or a SCSI-to-ESDI.
 
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