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Compaq Portable

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GAL

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Nov 22, 2009
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Mid Michigan 48623
I've got a Compaq Portable (luggable, sewing machine type) that won't fire up. The fan works but not screen, floppy dirve lights, etc. It worked many years ago when I put it away. Could it be as simple as a replaceable fuse somewhere? Any thoughts on where to start troublshooting?
 
The way to approach these things is to try to isolate the problem down to an area or component. These are generic guidelines to get started as I'm not familiar with the computer. Others might be able to give you more specific guidelines.

Open it up and see if there are any obvious fuses blown or cables which are disconnected.

Assuming things look ok, check it's not a power supply issue. Your fan goes, which means the power supply is at least getting power. Check the voltages which are coming out of the powersuppy into the mainboard. Check them while the board is plugged in. Are they showing the correct values (you'll need a technical manual to know what these are)?

If these seem ok, disconnect all cards and drives from the mainboard (if there are any cards) and/or power supply, leaving only the video connected. Switch it on and see if the screen springs to life. If it does, something on those things you disconnected is likely to be causing the problem. There may be a shorted capacitor or they just may be putting too much strain on an elderly power supply. If you get a result here, see if you can isolate the component that stops it from going, by systematically adding cards and drives.

Tez
 
GAL said:
I've got a Compaq Portable (luggable, sewing machine type) that won't fire up. The fan works but not screen, floppy dirve lights, etc. It worked many years ago when I put it away. Could it be as simple as a replaceable fuse somewhere? Any thoughts on where to start troublshooting?
Click to expand...

Will the computer start reading a boot disk on startup? Try connecting an external monitor to the unit and see if you get anything on that display.
 
afaik, it's a mains fan, but the monitor works off 12V, so more than likely the psu has packed up. If it's not gone bang, then usual reason why it won't start up is the "start-up capacitor" usually about 22uF and in the primary side of the switcher. If you're not familiar with electronics repair, there are lethal voltages in there so don't go experimenting. An old fashioned TV repair man should be able to help.
Edit:- just thought - I've had so many start up caps recently, I forgot about the main board tantalums.... next post!
 
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nige the hippy said:
afaik, it's a mains fan, but the monitor works off 12V, so more than likely the psu has packed up. If it's not gone bang, then usual reason why it won't start up is the "start-up capacitor" usually about 22uF and in the primary side of the switcher. If you're not familiar with electronics repair, there are lethal voltages in there so don't go experimenting. An old fashioned TV repair man should be able to help.
Click to expand...

I've already tried to "sandbox" it (remove everything to it's lowest form). The fan does run off of line (110v) voltage. Is the "start-up capacitor" used in the psu or are you talking about the monitor? I'm comfortable enough with electronics to know the basics and therefore REALLY break things. As you can imagine, everything is really a tight fit in this machine. There is a red led I notice on the motherboard that I thought lit or flashed for a second one time when I first turned it on, only once though.

EDIT:
I think I've figured out the fault.....the "Floppy/Printer Board". All is well until that board is installed then I get the quick led flash then nothing, pull it out and it boots from the HDD normally. Think an ISA floppy controller card would work.....is such a card made and available?
 
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Just one thing I totally forgot, have you tried unplugging the motherboard (I can't remember if it plugs in on this or not, sorry!) & running the psu on a dummy load like a known good(ish) HDD?
The tantalum filter caps on mother & daughter boards tend to go short, which trips the overcurrent protection.

The start up capacitor is actually in the power supply. it's a smallish electrolytic usually fed from a phsically big resistor (it's often a bit burnt too) straight off the rectified mains supply, it's there to provide a temporary supply to the primary side electronics before the supply starts up. Once the supply is running, current is usually provided from an auxilliary winding off the switcher transformer, and so it becomes redundant.
Usual symptom of it starting to go, are the power supply takes a while to start up after switch on. They often dry-up as they are right next to the big (hot) resistor.
 
I'm 99% sure it's the "Floppy/Printer Board". Remove it from the picture and all is right in the world. I'm emailing an EBayer that has a video card for sale from a like machine and asked him to check if he has a "Floppy/Printer Board" available. He was going to look and get back with me.
 
If you have a meter, try testing the tantalum capacitors on the floppy-printer board. (they're blobby with 2 or 3 legs & often orange or yellow) probably 4.7-10 uF. You'll probably find one or some are shorted. If it's "some" then there are more than one connected in parallel, and it's one of them that's gone. With a good low ohms setting you can sometimes look for the lowest meter reading, and guess that it's that one, snip it out and measure again, until the fault goes away. You can either replace them (check polarity, else BANG!) with tantalum or a small modern electrolytic, or you can leave them out altogether, and it'll probably work fine anyway.
Don't snip out the 0.1 uF decoupling capacitors by mistake (they're less blobby!) and generally don't fail.
 
Yes, Nige has some good advice there. it was a shorted tantalum capacitor on the floppy disk controller that stopped my AT from firing up when I first got it.

Tez
 
Would the ones to test be the orange or yellow (as a example) circled ones in this pic?
Which or in what area on the board is the "decoupling capacitors"?
Thank you so much for this suggestion!
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GAL said:
Would the ones to test be the orange or yellow (as a example) circled ones in this pic?
Which or in what area on the board is the "decoupling capacitors"?
Click to expand...

Id' start with the orange ones. The yellow ones, at least the uppermost two, look like decoupling capacitors (usually found next to ICs like these).
 
MikeS said:
Me too!
;-)
Click to expand...


I can confirm this was the situation .

Couldn't figure out why it was tripping the over current protection .
Found that the Orange one by the IC nearest to the edge was the culprit . I just tore it off in the mean time while writing it down to the parts list .

Mine is a compaq Portable Plus . I was so happy it was not a CRT issue .

now to get a 8bit ethernet card and I'm laughing .

For the record always pull out each card individually and wait between powerups / downs as the overcurrent needs to reset .
 
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