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View Full Version : Help Needed: Did I Mess It Up?



TicketMan4u
March 14th, 2016, 09:33 PM
Obviously no one can know for sure without looking directly at the computer itself but just for kicks and giggles for anyone out there who wants to take a stab at it, did I mess this computer up?

I lucked up and won what I believe are a couple of old 386's at an estate auction recently. I don't have a working monitor to check them completely but one powered up and run okay for several minutes with no apparent problems but the other looked like it started to come on then immediately shut down with the cooling fan making maybe only one or two revolutions before stopping.

I immediately shut off the switch and unplugged the cord but I know it was probably already damaged. My question is do these type of computers have a fuse or circuit breaker that trips to prevent damaging the entire system that I could check?

This computer has a DTK Model PIP-151 power supply. I believe it is a DTK Model DATA-1000

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modem7
March 15th, 2016, 01:33 AM
... but the other looked like it started to come on then immediately shut down with the cooling fan making maybe only one or two revolutions before stopping.
Based on that symptom, I think that there is high probability that a tantalum capacitor (see [here (http://www.minuszerodegrees.net/failure.htm)]) has gone short circuit, overloading the power supply. In my experience, this is more likely to occur if the computer has not been powered on in many years.

The short-circuit tantalum capacitor could be on the motherboard, on a card, or on a drive.

Do a good visual inspection because you may be lucky; the capacitor may have failed in a manner that shows itself visually.

Also, try the following:
* Power on after only the drives have been disconnected from the power supply. Leave motherboard and cards connected. If the power supply runs, the short-circuit is in a drive.
* Power on after the cards have been removed from the motherboard. Leave motherboard and drives connected. If the power supply runs, the short-circuit is in a card.

Note that turning on the power supply when nothing is connected to it, is not necessarily a valid thing to do, because many computer power supplies of the era require a certain minimum amount of loading. Each different model of such power supplies has its own minimum loading requirement.

TicketMan4u
March 15th, 2016, 08:59 AM
Thanks for the help modem7. I'll take a look at everything as you've suggested and report back later. Thanks again.

TicketMan4u
March 15th, 2016, 03:23 PM
I looked as best I could without taking anything apart but could not see any evidence of anything burned or overheated. Next without being redundant about safety around electrical components I unplugged wiring to the floppy drive then connected to power source and turned unit on but nothing happened. Left floppy drive disconnected and disconnected hard drive and tried again with same result. Then I reconnected floppy and hard drives and disconnected motherboard and tried again but still nothing happened. I did not see where power supply was connected anywhere else. May try to take it apart now to see if I can see anything now. Thanks for the help.

TicketMan4u
March 16th, 2016, 07:18 AM
Took the boards out and still nothing obvious jumped out at me as looking burnt. I hope to find out what's wrong soon as I would at least like to be able to say machine powers up when I sell it.

Chuck(G)
March 16th, 2016, 07:59 AM
Many people recommend a visual inspection. I usually go one better and do an olfactory inspection; that is, does any component smell burned?

If you've connected a known-good hard drive to the power supply and disconnected the power supply from the motherboard and other drives--and it still plays dead, then it's the power supply. Not beyond hope--you can open the power supply and repair the PCB (s) within.

MicrocomputerSolutions
March 16th, 2016, 01:28 PM
Many people recommend a visual inspection. I usually go one better and do an olfactory inspection; that is, does any component smell burned?

If you've connected a known-good hard drive to the power supply and disconnected the power supply from the motherboard and other drives--and it still plays dead, then it's the power supply. Not beyond hope--you can open the power supply and repair the PCB (s) within.



If the OP doesn't know how to do a basic power check on a PC, it's doubtful if he has the knowledge and experience to repair a switching power supply.

DTK was a known import/manufacturer in the early days of PC Compatibles. There's a good chance that the power supply is bad. The thing is over 30 years old and old switcher never lasted more than 2-3 years in most cases from my experience.

If the two computers are both AT case compatibles, he could try swapping the power supply from the working computer into the non-working one. If he does want to do that, he should sell the non-working computer as not-working, as is for parts or repair, and let it go cheap. It isn't worth much anyway, unless it has a big hard drive from a major brand, and/or other valuable components like a Creative Labs Sound Blaster card or name brand video card.

Chuck(G)
March 16th, 2016, 03:31 PM
If the OP doesn't know how to do a basic power check on a PC, it's doubtful if he has the knowledge and experience to repair a switching power supply.

Perhaps, but desperation is a great teacher. :) At any rate, it could be something as simple as a blown fuse.


DTK was a known import/manufacturer in the early days of PC Compatibles. There's a good chance that the power supply is bad. The thing is over 30 years old and old switcher never lasted more than 2-3 years in most cases from my experience.

I'd better toss out my 40-year old open-frame switchers that I got from Bob Boschert, then, huh? Oddly, they still work fine. :)

TicketMan4u
March 16th, 2016, 07:15 PM
I may not know how to do a basic power check on a PC or have the knowledge and experience to repair a burned out power supply but I can follow directions. And the main reason I joined this forum was to hopefully learn from those with more knowledge and experience.

MicrocomputerSolutions
March 16th, 2016, 08:34 PM
Perhaps, but desperation is a great teacher. :) At any rate, it could be something as simple as a blown fuse.



I'd better toss out my 40-year old open-frame switchers that I got from Bob Boschert, then, huh? Oddly, they still work fine. :)


A 40-year old open frame: two, three, four (or more) hundred dollar Boschert Switcher is not the same thing as a $20 Korean or Taiwan made AT clone power supply.

Compupro was charging $500 to repair (two week turnaround), or $1K to replace (with exchange) the Boschert that was used in the late model Compupro Switcher S-100 Systems. I would not dream of tossing one of those away, since there aren't any more (and haven't been for years). But I probably would not try fixing one if I needed to, either. I'd send to out to a Specialist, and let them sweat the repair.

Chuck(G)
March 16th, 2016, 08:39 PM
The earlier suggestion was good--try swapping the power supply that was good. At least that way, you'll know what works. Most PSUs are protected from short circuits, so you're really not in much danger of toasting it to a smoky goodness. Worst case, you can probably buy one off of eBay.

Chuck(G)
March 16th, 2016, 08:46 PM
A 40-year old open frame: two, three, four (or more) hundred dollar Boschert Switcher is not the same thing as a $20 Korean or Taiwan made AT clone power supply.

These date from about 1977 or so--Bob was pretty much still building them by hand. He made a huge difference in the computer industry. After years of linear supplies with huge transformers, you could actually make a computer that was easy for a person to lift. I recall seeing a pile of surplus switchers at Haltek that blew my mind--about the size of a lunchbox, 5V at 200A.

Bob is still around, the last I checked.