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Suggestions before IBM 5150 Power Up

J

jwhitney

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I'm restoring an IBM 5150, from 1982, with the 63 watt black power supply. This is a two FDD, 16-64K MB unit. It arrived with 29 years of dust inside. Before applying power I have totally cleaned everything, including the inside of the power supply, taking everything apart, and even garden hosing the bare black chassis (I didn't get the paper SN label in back wet). Now I am putting everything back together. Is there anything the forum's 'IBM 5150 experts' would recommend I do prior to power up? Should I power up the 63 watt power supply without the MB connected to test voltages? Also I notice the FDDs do not have the IBM logo on the front black plate, but they do say Tandon and have an IBM CORP paper label on the FDD metal chassis. Did early 5150 FDD's not have the IBM logo on the front of them? Also the speaker has no cloth tag on the wires. Did all IBM's have that date of manufacture cloth tag on them? I did unstuck one FDD and lightly oiled the motor shaft and the two re-write head slide rails. Was this ok? I have my fingers crossed that I have not screwed up anything while deep cleaning everything. Thanks.
 
The PSU will not operate without a load. Just power the bugger up--the power supply has overload protection, so if there's a short, it won't come up.

Also note, that just because the fan is running does not mean that the power supply is good--the fans on the early 5150 PSUs were line-operated AC units.

The IBM-logoed faceplates were not on the initial run of systems.
 
modem7 said:
My early 5150 does not have one.
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My early 16-64k 5150 does not have one. My later 5150 from 1984 does. Interesting difference between the cases on mine is that the early version only has two bolts securing the case cover on the back, one in each lower corner. The later version has the customary 5 bolts.

When starting up an old system that has not been powered on I like to leave the case cover off and darken the room, then throw the switch. It has helped me know which capacitor shorted on more than one occasion.
 
RJBJR said:
My early 16-64k 5150 does not have one. My later 5150 from 1984 does.
Click to expand...

Neither did mine.

When starting up an old system that has not been powered on I like to leave the case cover off and darken the room, then throw the switch. It has helped me know which capacitor shorted on more than one occasion.
Click to expand...

What's the fun in that? You let all of the magic smoke out... :) Having a good nose also helps a lot. Sniffing to zero in on a bad component (with the power off) is a very much overlooked troubleshooting tool.
 
Chuck(G) said:
Neither did mine.



What's the fun in that? You let all of the magic smoke out... :) Having a good nose also helps a lot. Sniffing to zero in on a bad component (with the power off) is a very much overlooked troubleshooting tool.
Click to expand...

I like the excitement from a power-on. Sniffing around is a good way too, nothing compares to that burnt electrical smell.
 
The PSU in my 5150 had bad filter caps in it marked "RIFA" which needed to be changed, one was cracked and the other had exploded, which apparently is due to bad resin compound which absorbs moisture, then explodes when powered up. With those changed the PSU did fire up with no load, and consumed 22w at the wall socket. As said visually inspect the electrolytic caps in the PSU and using your nose will help too!

Check the fan spins freely. It's mains powered so will spin even if the rest of the PSU is dead.

Also while you have the mobo out carefully visually check all the tantylum bead capacitors as they are known to blow also.

Do post how testing goes!
 
That being said, a power supply will usually run just fine with bad line filter caps. The idea is to keep RF from the computer out of the mains. They do not affect the operation of the PSU. Whatever, do not replace them with the same devices--RIFA polystyrene-encapsulated paper capacitors are bad news, though they're sought after by audio enthusiasts. Go figure. Polyester caps rated for the same application should last a bit longer. Check the forum for "RIFA".

As far as tantalums go, they may surprise you when they let go, but again, they won't hurt anything if they do go POP. Film bypass capacitors (all over the board) have also been known to imitate Orville Redenbacher's finest product. Again, one or two little firecrackers won't hurt anything as strictly speaking, they're not essential to operation.
 
RJBJR said:
I like the excitement from a power-on. Sniffing around is a good way too, nothing compares to that burnt electrical smell.
Click to expand...
Same thing that happened when I first flipped the switch on my Dell System 310. I turned it on, and POW!!!, something blew, and let the smoke out.
After a few weeks of sitting in the closet, (just like old hard drives sometimes do), it works again.
 
What's inside the 5150 power supply? I've been investigating the history of switching power supplies lately (which is more interesting than you'd expect) and I'm really curious what controller IC was used in the original IBM PC power supply. There doesn't seem to be any information on the web - the power supply is just a sealed box to most people. But since you guys have been poking around inside the PSU, hopefully you can share your discoveries with me.

Thanks,
Ken
 
Apparently, there wasn't just one power supply--and I don't believe that IBM ever published a schematic.

At 63 watts, an awful lot of them were tossed out and replaced with third-party PSUs with a bit more power capacity.

I can tell you that mine used an AC line-powered fan.
 
A SAMS Computerfacts of the 5150 includes a circuit diagram of the power supply. In that diagram, the switching IC is shown as "221-233". It should not be assumed that the 221-233 was used in all versions of the 5150 power supply.

A quick web search did not show details of "221-233".

Other semiconductors in the power supply are shown in the diagram as having part numbers that start with "221-", and so maybe these part numbers are being used by the maker to mask the real part numbers.
The op amp ICs are shown in the diagram as part numbers 221-129A-01 and 221-121B. 221-129A-01 shows as an op amp at http://www.oocities.org/waklobe/opamps.htm
The -5V regulator is shown in the diagram as 221-192-01. NTE961 (-5 Volt 1A Voltage Regulator) is shown on the web as a replacement for 221-192-01.
 
I always start a psu up first time on a low load (e.g. a C**P old hard disk drive) & with a lightbulb in series with the mains. That way if there are shorts or it's drawing too much current, the lightbulb turns on. It's good because you can keep an eye on the current consumption by the glowing of the bulb. 100W should be fine for a 5150 psu.

I'm FINALLY getting my proper mains control box sorted. Variac, analogue ammeter & selection of series light bulbs (25W, 100w & 500w, plus straight through) on a switch.
 
Thank you modem7; your information about the 5150 power supply was really enlightening. By studying that schematic, I conclude that the 221-233 switching IC has to be a TDA1060/NE5560 SMPS controller IC.

One surprising thing about the schematic was how many components the power supply uses; about twice the part count of an Apple II supply. The design looks straightforward enough: voltage doubler to produce 325V DC, the NE5560 driving a power transistor through a drive transformer, and a flyback transformer with the multiple outputs (with additional regulation on the -5 and +12 outputs). The +5 provides voltage feedback to the controller IC, and the POWER-GOOD signal comes from comparators on all 4 outputs testing against high and low limits. Whoever designed this power supply must have loved op amps, as it uses 11 in total. Both the voltage feedback and power-good are connected to the controller IC through optoisolators. (Maybe that's more detail about the power supply than anyone wants :)

If anyone knows more about other 5150 power supply models, I'd like to hear from you.

Ken
 
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