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bluethunder
September 11th, 2010, 12:47 PM
I drug my old compaq portable out, which I knew didnt work, and tried some basic troubleshooting on it..

Turned on.. Dead..

Checked for power on the floppy connectors, nothing.

Pulled all the cards, unplugged the mainboard and floppies. Nothing.

Unplugged the monitor power then I had +12 for a few seconds, then nothing again.

Wiggled some of the power plugs on the board, powered up and had 2 pops and the stink of burnt electronics.

After stripping the machine to nothing to get the PS out, I see that 2 tant. caps have exploded C39 & C37. 2.2-25 is written on the side of one of them thats still legigble..

I'm going to go an replace all the 2.2-25, and the 15-25 tant caps.

Is there any others I should be looking out for?

Chuck(G)
September 11th, 2010, 01:59 PM
Not unless they're causing problems. I generally just let them explode when they want to, then replace them. You might even be able to replace them with electrolytic caps if you can't stand the noise.

MikeS
September 11th, 2010, 03:19 PM
You might even be able to replace them with electrolytic caps if you can't stand the noise.
:rofl:

bluethunder
September 11th, 2010, 05:59 PM
Well, i replaced those 2 caps, and got the power supply working, screen comes up.. It even boots..

Now it turns out the keytronic keyboard is hosed. The foam pads have disintegrated.

Any one know if the compaq uses a same protocol as a standard xt keyboard?

JohnElliott
September 12th, 2010, 11:13 AM
The Deskpro does, so it's quite likely that the Portable does, too.

mikerm
September 12th, 2010, 01:17 PM
I JUST got another Compaq Portable on Friday. I haven't torn it apart yet, but it looks like our power supplies have/had the same problem.

I looks like the 2 portables I have a re different revisions. The one I just got appears to be newer, and the cards are smaller and less populated. I'm not sure it the newer one is any better internally, but it does have a better case. At any rate I will be combining them into one and making a really nice one. I still gotta tear into it though to get that board fixed.

james1095
September 15th, 2010, 04:14 PM
I see no reason why they couldn't both be resurrected. Sounds like the problems are pretty minor.

james1095
September 15th, 2010, 04:16 PM
Not unless they're causing problems. I generally just let them explode when they want to, then replace them. You might even be able to replace them with electrolytic caps if you can't stand the noise.

Electrolytic caps typically have much higher ESR. This may or may not be a problem, but if you use electrolytics I recommend a .1uF ceramic cap in parallel with each. They're small enough to be tacked on the bottom of the PCB.

Chuck(G)
September 15th, 2010, 04:36 PM
Electrolytic caps typically have much higher ESR. This may or may not be a problem, but if you use electrolytics I recommend a .1uF ceramic cap in parallel with each. They're small enough to be tacked on the bottom of the PCB.

In most of the applications I've seen, the tantalum is used for decoupling, with a 0.1 uF film cap at every IC location for bypass. ESR in this case shouldn't matter--what you really want is storage capability to keep the DC supply stable.

If these were filter caps in the power supply, ESR can matter a lot.

bluethunder
September 23rd, 2010, 08:06 AM
Ever since I replaced the caps in the PS, it has been powering up fine..

Too bad about the QUADRAM that was in it, the battery leaked, and the machine won't boot with the card in place. A little text error, and thats it. I might try cleaning it up, and see if I can make it work. I went and desoldered the clock battery in my PS/2 at the same time, before it puked everywheres too.

Sure glad, at sometime in the past, some one replaced the 6000 torx screws with phillips heads. That thing was engineered to survive an atomic strike I think.

Now, to try hacking a connector up to connect a standard XT keyboard to it, until I get around to rebuilding the keytronic keyboard foamies.

Does any one have the SAMS book on the compaq portable? Is it worth getting to repair these machines?

james1095
September 24th, 2010, 02:29 PM
The electrolyte in NiCd cells is alkaline, so a scrub with white vinegar and a toothbrush is a good start, followed by a rinse with warm soapy water. Corrosion can bridge pins or track up into the IC body and rot out bond wires so I usually replace any ICs with significant corrosion on the pins and clean the crud out from under them.

The first thing I do with any "new" old computer, arcade game, pinball, or other item with a backup battery is pull the battery, most of the time if they're still there, they've already leaked and sometimes the damage is extensive. To make matters worse, it alters the solder it gets on, significantly increasing the melting point making it more difficult to remove parts without damage to the pads.

Chuckster_in_Jax
September 24th, 2010, 06:58 PM
After stripping the machine to nothing to get the PS out, I see that 2 tant. caps have exploded C39 & C37. 2.2-25 is written on the side of one of them thats still legigble..

Does this look familiar?

http://yfrog.com/ht002kpj

bluethunder
September 26th, 2010, 05:05 PM
Holy moly..

Its a twin to mine, except i was able to read one of the two, to get the size off of them..

Kinda creepy really

Chuckster_in_Jax
September 27th, 2010, 08:55 PM
Does this look familiar?

http://yfrog.com/ht002kpj

Well, this post got me motivated to work on my Compaq Portable. Replaced the blown tantalums and it still wouldn't power up. Noticed that the neck of the CTR glowed for a brief moment then turned off. Unplugged the power connections to the video board and the motherboard and the power supply started working. Checked the mobo for shorts and found continuity between +12v and ground and -12v and ground. There were tantalums across those supplies so I removed them and the short is now gone. Hooked the mobo and video back up and I get 2 beeps from the speaker. Looks like the unit is running again so I put the other cards back in and power it up. I get a loud snap and a burned smell. Did I drop a screw during reassembly? Turned the computer upside down and a small wrench falls out.

WTF!!!!! Now the thing is dead again.

Don't think it's going to be so easy to repair this time.

bluethunder
September 28th, 2010, 09:31 AM
Oh damn!

Hopefully its another obvious repair, with some really cooked components. Where did the wrench fall out of?

Don't forget to check the fuse that's in the 3 pronged AC plug. Might have gotten lucky, and only blown that.

Chuckster_in_Jax
September 29th, 2010, 07:39 PM
Took another look at my Compaq Portable today. Since I got it I found the following shorted tantalums.

2 in the power supply
2 on the floppy controller(one burst into flames when I powered the unit)
2 on the main board
1 on the Video Adapter

That's seems like an awful lot of bad tantalums.

The unit will power up, but halts with a screen full of characters and a continuous beep from the speaker. The service manual says the continuous beep indicates a bad power supply.

I took voltage readings with my multimeter from one of the ISA sockets on the main board and got this:

+5v = +5.07v
-5v = -4.97v
+12v = +12.36v
-12v = -12.05v

Those look OK to me. The -5 was a little low. Don't know if that would be a problem.

Tomorrow I'll do some more troubleshooting on the MoBO. See if there is a problem with RAM. The first 2 banks are soldered in and the other 2 are socketed.

Chuckster_in_Jax
September 30th, 2010, 08:06 AM
I have a couple of questions before I continue troubleshooting.

1) Given the voltages I read off the main board and the fact that I get a continuous beep from the speaker several seconds after the computer is turned on, could I assume that the CPU is up and running.?

2) Is it possible that the diagnostics are running and just get to a point before the video ram is initialized and trigger the speaker to beep. Or is it more possible that there is some part of the circuitry that will cause the speaker to beep if it doesn't get a response from the CPU?

james1095
September 30th, 2010, 03:27 PM
Is there a Power Good line from the power supply? Most PC power supplies have that, it goes high once the PSU detects that the voltages are stable, which tells the motherboard to release reset and start up. If the PG circuit is bad, the machine will detect a bad PSU. It's been years since I've been inside a Compaq portable and Compaq machines tend to be a bit odd in a lot of ways.

modem7
September 30th, 2010, 03:37 PM
All a continuous beep from the speaker informs you of is that your speaker is working, and that at least some of the circuitry that generates tones for the speaker is working.

On either an IBM 5150 or 5160 motherboard (could be both), simply removing the BIOS ROM will result in a continuous beep from the speaker.

bluethunder
September 30th, 2010, 04:24 PM
Took another look at my Compaq Portable today. Since I got it I found the following shorted tantalums.

2 in the power supply
2 on the floppy controller(one burst into flames when I powered the unit)
2 on the main board
1 on the Video Adapter

That's seems like an awful lot of bad tantalums.

The unit will power up, but halts with a screen full of characters and a continuous beep from the speaker. The service manual says the continuous beep indicates a bad power supply.

I took voltage readings with my multimeter from one of the ISA sockets on the main board and got this:

+5v = +5.07v
-5v = -4.97v
+12v = +12.36v
-12v = -12.05v

Those look OK to me. The -5 was a little low. Don't know if that would be a problem.

Tomorrow I'll do some more troubleshooting on the MoBO. See if there is a problem with RAM. The first 2 banks are soldered in and the other 2 are socketed.

As far as voltages go, those all look ok.

What area did the wrench fall out of, it sounds like a chip got cooked when it shorted.

If you can find an ISA POST card, they are the gateway to fixing all kinds of problems. If you get a landmark or similar type of card that has ROM based diagnostics, they are even better.

At the very least, they will tell you if the CPU is running, and what point the computer fails the POSTs. Or if its running at all.

Chuckster_in_Jax
September 30th, 2010, 05:48 PM
Is there a Power Good line from the power supply? Most PC power supplies have that, it goes high once the PSU detects that the voltages are stable, which tells the motherboard to release reset and start up. If the PG circuit is bad, the machine will detect a bad PSU. It's been years since I've been inside a Compaq portable and Compaq machines tend to be a bit odd in a lot of ways.


OK, there is a Power Good signal. Checked the voltage at the main board and got 4.41v. Disconnected the cable from the board and the signal measured 5.00v. So it looks like there is a problem there.

Chuckster_in_Jax
September 30th, 2010, 05:54 PM
As far as voltages go, those all look ok.

What area did the wrench fall out of, it sounds like a chip got cooked when it shorted.

Don't know where the wrench was. It may not have caused any damage. The pop sound may have come from one of the many tantalums that were bad.


If you can find an ISA POST card, they are the gateway to fixing all kinds of problems. If you get a landmark or similar type of card that has ROM based diagnostics, they are even better.

At the very least, they will tell you if the CPU is running, and what point the computer fails the POSTs. Or if its running at all.

I've thought about getting one of those cards in the past. Looks like I need to break down and buy one. It would save a lot of time.

bluethunder
September 30th, 2010, 06:38 PM
I bought a Landmark Kickstart IRQ years ago, and its been a trusty helper for ISA based stuff.

As soon as I get my keyboard repair kit for the portable, I'm going to throw it in, and see how it works in the portable, and if it will help you at all..

modem7
September 30th, 2010, 07:28 PM
OK, there is a Power Good signal. Checked the voltage at the main board and got 4.41v. Disconnected the cable from the board and the signal measured 5.00v. So it looks like there is a problem there.
The drop in voltage will be due to the motherboard 'loading' the signal. A slight voltage drop is expected.
The PWR GOOD signal from the PSU goes directly to the RES pin on the 8284 chip on the 5160 motherboard.
The 8284 is a TTL chip. Therefore, the PWR GOOD signal would have to drop significantly lower (below 2V) to cause a problem.

0 to 0.8V = logic low
0.8V to 2V = "no man's land"
2V to 5V = logic high

Chuckster_in_Jax
October 11th, 2010, 03:07 PM
Found the main problem. It was a RAM chip in the first bank. Used the piggy back method and it worked. While I was troubleshooting I first got a message on the CRT "Parity Check 1". Turns out that means there is a memory error on the onboard RAM. If it gives "Parity Check 2" that means the bad RAM is located on an add-on board. After fiddling with it for while, it displayed briefly an error code telling what Bank and chip was bad, immediately followed by a screen full of characters and a continuous beep.

With a good RAM piggybacked, the computer will boot from floppy and ask to change the Date/Time. But for some reason the keyboard doesn't respond to any key. I'm wondering if the keyboard or keyboard circuit may be bad, or if needs a specific boot disk for this machine.

bluethunder
October 12th, 2010, 09:46 AM
My machine is in the exact same state right now.

The foam in the keyboard has completely disintegrated, rendering every key dead.

If I strip the keyboard down, and touch the pads, i can make garbage appear on the screen, so I know that the keyboard, and compaq are talking.

Waiting for my ebay repair kit to come. If it works, I will pass on the info to you.

Should change this thread name to "Help my compaq portable is #$%@ed", since its grown beyond fluxing capacitors.

bluethunder
October 12th, 2010, 06:58 PM
Turns out SAMS has the photofacts available for this machine.. https://www.samswebsite.com/en/photofact/search/index/brand/COMPAQ

Could of used that about a month ago, but I have it now..

Complete schematics for this POS.

Keyboard update..

I replaced all the foamies and mylar disks, with a kit.. Still doesn't work.

I think there is something wrong with the keyboard.

Atleast with schematics, I have something to work with.

Chuckster_in_Jax
October 12th, 2010, 08:09 PM
I got the SAMS photofacts also. There is a section on troubleshooting the keyboard. If you have an external power supply, you don't need to have it hooked up to the machine to troubleshoot it. I should be able to check mine out tomorrow.

Note: The keyboard cable on mine looks like it has been pinched where it enters the keyboard. Possible a wire could be damaged. You may check for broken wires or even a short in the cable.

bluethunder
October 12th, 2010, 08:21 PM
well, after doing some digging on the keyboard..

Looks like a Exar 22-950-3b chip is cooked. Every other set of pads has .8v on it. Ones attached to pin 14 on it, have 4v accross them.

Don't hold alot of hope to find that chip. Can't even find a data sheet.

I did find a pinout on a apple lisa site, so thats something.

Chuckster_in_Jax
October 13th, 2010, 07:13 PM
Checked out the cable on mine tonight and I can't get continuity between any of the pins. Looks like I'll have to make a custom cable even if it's a temporary one.

Jtterbug
October 28th, 2010, 06:04 AM
I have q COMPAQ, But the Fan only goes, what could be wrong?

bluethunder
October 28th, 2010, 11:49 AM
Either you have a short someplace in the compaq, or the power supply has gone south.

Step 1 Unplug a floppy drive, and check the Voltage at the plug. The floppy power plug is +5 0 0 +12, so outside to the middle pins should be +5, and the opposite outside to middle will be +12V.

Step 2 would be pull all the cards, and unplug the drives, and check voltage again on the floppy power plug.

Step 3 Unplug the monitor, and motherboard power connectors, check voltage.

If its still dead with nothing connected to the power supply, then the power supply is probably dead/shorted.

2 of us here, have had a pair of capacitors die horribly on the power supply, that are easily replaced.

bluethunder
October 28th, 2010, 11:51 AM
Checked out the cable on mine tonight and I can't get continuity between any of the pins. Looks like I'll have to make a custom cable even if it's a temporary one.

I got a spare compaq for parts (mostly the keyboard). So I might have an extra keyboard cable.

Jtterbug
October 28th, 2010, 03:16 PM
Oh, I forgot, The LED on the motherboard comes on.