Compaq Armada 3500 wont start.

[Wappynutter]

Hi all..
Quick question to the VCF hive mind.
Compaq Armada 3500 pentium 300 64mb ram built in. Purchased 10 or more years ago off a popular auction site.
Purchased as spares or repairs, no psu, untested. Arrived smashed screen and with no way to test it I put it in the stash.
Jump forward to 2023 and with a bench psu and some bodge wires as this is an uncommon sickle tip charger. I supplied the required volts and amps, tested power was getting to the motherboard and yes, we have power but....
Doesn't turn on, seems to supply 2volts to the battery charge rail. No lights, smells warm so took a sniff and felt the heat coming off 3 of the capacitors on the the powerboard.
Most were warm but 3 were to hot to touch.
I'm guessing these are my startup problem.
There are signs of some professional repairs on the back of the board so I'm fairly sure that isn't an issue. I just want to check for life in this old laptop before I commit to purchasing a replacement screen and a psu.
Repair documentation is next to nothing, even YouTube info is limited.
I can order some low profile 100uF 25v caps and replace I'm just wondering if others have had a similar scenario or have any information on the Armada 3500. Thanks in advance, let try and save another vintage laptop.
(pictures of the powerboard info, caps that are warm, top 3 in 3rd picture are the hot ones, powerboard on the motherboard under the keyboard, last 2 pictures show repairs.)

 

[GiGaBiTe]

"Professional Repairs" - Those are factory bodges to fix errors in the PCB design.

As for the capacitors getting hot, capacitors should never get hot, or even warm. If they are, there's something very wrong with them, or something in circuit with them. Laptops of that vintage are notorious for bad capacitors, you'll need to replace all of them, not just the ones that are getting hot.

Once you replace them, start looking for shorts, if the power rails are being dragged down, there's something dead. It looks like you may have tantalum capacitors on the main board, you should check those.

 

[3lectr1c]

Just a note, make sure there aren't any NiMH or NiCad backup batteries hiding anywhere inside. Some of the Compaqs had them and they leak and ruin anything near them.

 

[Wappynutter]

"Professional Repairs" - Those are factory bodges to fix errors in the PCB design.

As for the capacitors getting hot, capacitors should never get hot, or even warm. If they are, there's something very wrong with them, or something in circuit with them. Laptops of that vintage are notorious for bad capacitors, you'll need to replace all of them, not just the ones that are getting hot.

Once you replace them, start looking for shorts, if the power rails are being dragged down, there's something dead. It looks like you may have tantalum capacitors on the main board, you should check those.

Lol.. yeah, "professional repairs" was me being polite so I didn't offend .. lol. What a screwed up way to bodge a trace or two.
I was certain that the toastie caps were a no no. I'll replace like for like, low profile etc.. and see how we go. I'll check for a short after as I'm sure this powerboard is the problem. It sits snug under the keyboard. It connects to the mainboard via through hole connectors and pin headers.
Thanks again for the input, appreciated.

 

[Wappynutter]

Just a note, make sure there aren't any NiMH or NiCad backup batteries hiding anywhere inside. Some of the Compaqs had them and they leak and ruin anything near them.

Thanks for the input. Yeah seen a few rotten boards and dead hardware due to battery leakage.
Luckily this slimline Compaq mobile variant has the battery packs in the hdd area on plugs.
All good, dead, not leaked and put back in for the photo shoot only. Seems to be the pair of AA battery type 3v and what looks like a pair of watch button batteries.
Not noted any more suspect chips on the board.
Thanks again..

 

[3lectr1c]

There's a guy on eBay building new CMOS batteries: https://www.ebay.com/itm/325046056703
You don't need to replace the AA style pack, that would likely be a mechanism to keep the computer in sleep mode when swapping out the main battery pack, so you don't have to do a full reboot.

 

[Wappynutter]

There's a guy on eBay building new CMOS batteries: https://www.ebay.com/itm/325046056703
You don't need to replace the AA style pack, that would likely be a mechanism to keep the computer in sleep mode when swapping out the main battery pack, so you don't have to do a full reboot.

Thanks for the info. Will save the link and see how it goes once/if I get it up and running.
Fingers crossed a handful of capacitors cure the non starter.

 

[Wappynutter]

So.......
We now have power after a part recap of the dc/dc powerboard.. but....
We are on then off powerswitch wise...
It's like We have a short that shuts the board down. Why do I think this?
Well if I remove the MMC-1 280 pin 300mhz cpu card the motherboard powers up and stays on, cpu card installed and it shuts down straight away.
If I force it to stay powered by holding the powerswitch on the cpu warms quickly so I let it shut down to save any further damage.
I've done the finger test for heat elsewhere but nothing topside seem hot, just the cpu core.
Also buzzed out the capacitors and found no detectable shorts on the cpu card.
Is it the cpu? Does it need a reflow or reball?
This would cause a problem as the heatsinks are riveted in place and I can see the thermal paste around the edges. Maybe the paste is not where it needs to be?
Google and all the usual searches come up blank. Info on the cpu card is limited so I don't know where to start. I have a pdf tech sheet off the wiki. I could swap out for a similar secondhand card purchase but it would be a slower cpu, and I'm reluctant to replace the entire board if it's a chip, resistor, capacitor, mosfet problem.
This old laptop seems quite rare, even YouTube searches are low.
Any MMC-1 cpu experienced minds have any ideas what could be causing the laptop to instantly shutdown when the card is installed?.
Thanks in advance for any info..

 

[Wappynutter]

So... maybe scratch the previous post.
As I stated I went around buzzing capacitors on the MMC-1 board, the motherboard and then rebuzzed the dc/dc power distribution board and found 2 capacitors that have continuity.
C14 and C35 both buzz and zero to ground.
Both seem to link to adjacent vacant pads. Wondering if the ground is as expected or the failure of 1 or both caps.
Any input would be appreciated before I bring out the hot air station.
Thanks VCF hive mind.

 

[3lectr1c]

take them out of circuit and then check - if they're still shorted, replace them.

 

[Wappynutter]

I'll dig out some removal gear and buzz them when I get the chance. Thanks for the quick reply.

 

[Wappynutter]

So buzzed the caps at c14 and c35 on the powerboard as they were shorted to ground and before I removed and did this I followed the traces to the pins on the chips
The chip LTC1435CS shows pin 10 which the caps go to are ground chips.
I'm guessing that's why they buzz out.
Upon removal both caps tested fine, no shorts.
I didn't check ohms but it's safe to say they gonna be fine so back to the MMC-1 cpu idea.
I'm looking at a "spare" MMC-1 I have in the stash from a Toshiba but its a PMD23305002AB. Making it a 233mhz instead of the 300mhz original, but more so its an AB not an AA as the original. Does anyone know the difference and if it would be okay for testing at least?.
So close to getting this working now I'm sure. Then if it outputs to an external display I might be tempted to source a replacement screen.
Thanks again for any input, appreciated.

 

[Wappynutter]

So quick check, the 23305002AB is 1.7v core voltage where as the original cpu module 30005002AA is 1.6v core voltage.
So I'm guessing yes it would fit but could be unstable or not work as it's v core is under the spec voltage. Also I did check the capacitor pads once I'd removed the caps and still got beeped out. Guessing it's still shorted or is supposed to be as its on the ground plain.

 

[Wappynutter]

So... tried the different cpu module but still shuts down. Almost a beep on beep off scenario..
Cpu module removed and the motherboard stays powered on.
Anybody have a Compaq Armada 3500 motherboard schematic to trace voltages.
Thanks in advance for any help or advice, appreciated.

 

[Wappynutter]

Had an hour today so set up and started probing and checking about the board.
Power supply connected and still we beep on beep off like it's shorted out maybe??
Anyway, power connected, not turned on obviously as it instant shuts down and I start to check both sides of the motherboard, finger test for anything hot first.
...and I may have found something.

Big yellow cap at c673 seems to get warm quickly. This part of the board is under plastic film shielding so I unstuck it hence the glue marks and checked again. This area is warmest on the board. Multimeter in continuity and we beep both sides to earth.
Power unplugged and we back to normal beep only on the left side in the picture.
Checked through the veer with 0.2mm wire to see where it goes.

Center left of picture, the veer between the yellow caps. Going to 2 pins on the plug which I think the screen goes to. The screen is smashed, doesn't power on or light up and came like this through the post 10+ years ago.
Poorly packaged when I brought it off ebay.
Still got more checking to do but could this be the short shutting it down?
Question is, how would I determine the capacitance of the cap to try a new one if it is indeed shorted? Could the smashed screen have contributed to the short when the screen got broken? I did Power up the system once I replaced the caps on the powerboard to see if the screen lit up, which it didn't, and I'm sure it stayed powered on first try.
Thanks again for any input, greatly appreciated.

 

[T-R-A]

It's possible but somewhat unlikely for ceramic capacitors to short. I'm hoping you're not doing that continuity test with the power on.... could easily damage the board and/or your meter.

Only way to know for certain is to remove the capacitor from the circuit and check it for being shorted. If so, you'll need to find a reference or another exact board to again remove and measure it's capacitor (with a capacitance meter).

If it's not shorted, then something else (think transistors/regulators/diodes) likely is.

 

[Wappynutter]

No, no power on, I'd fry myself and the board... Big bang etc...
I'm wondering about the transistor located above the cap.
As far as exact reference I may struggle as the board is rare it seems. Next to no info or reference about.
Found the manual but little else. Thanks for the input.

 

[GiGaBiTe]

Power supply connected and still we beep on beep off like it's shorted out maybe??

You really shouldn't be using continuity mode to check for shorts in that circuit. Continuity mode on a multimeter will generally beep if it sees anything less than 50 ohms, but the problem is that the CPU and power regulation runs on 5 volts or less. The resistance of components in that area is going to be very low in normal operation, and will give you false readings.

You should be using resistance mode instead and look for very low resistances, like less than 5 ohms.

You'll probably have to resort to voltage injection into different parts of the circuit to figure out where the fault is. You'll need a bench power supply for that so you can limit the current and avoid blowing a crater in the board, or frying the CPU.

It's possible but somewhat unlikely for ceramic capacitors to short.

MLCC ceramic capacitors are ridiculously fragile, and it goes up exponentially with the higher farad ratings. The stacked wafers are so thin that even slight mechanical stress with the wrong kind of solder from heat or board flexing can cause them to crack and short.

It's such a problem that some PCB designs put large MLCC caps on their own section of board with channels routed in the board to reduce deflection and heat sinking.

 

[Wappynutter]

Thanks for the info GiGaBiTe, I'll get on it when I have 5 mins.
As far as power goes I am using my bench power supply as mostly these compaqs sold with the docking station which uses a standard power cord. My unit is on its own and requires a 3 pin sickle tip 15v psu which I don't have and is rare as hens teeth. I've chased faults around the board as documented. I'm guessing power doesn't reach anywhere when the cpu module is removed hence why it will stay powered when the module is removed.
Something I had noticed is the power switch doesn't work on its own. I have to use the suspend/resume button also to turn on.
Originally I had to recap the dc/dc board to get it to even start and considered a short on there, then cpu module but it could be anywhere at this point.
So I'll check resistance soon and pray. Lol..
Thanks again for the input.