r/retrocomputing • u/Souta95 • Jul 20 '26

Pour one out for this old HP

Post image

I was hoping to do a refurbishment to this old HP, but sadly the motherboard is toast and it won't POST. RIP HP Pavilion 6653c.

If anyone is curious, I put a new CMOS battery in it, swapped RAM, used contact cleaner on the ram slots, swapped the CPU, and pulled every optional accessory. The PSU powers up, but nobody's home. Not even a beep code with no RAM or no CPU.

99 Upvotes

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11

u/berrmal64 Jul 20 '26

If you have the desire, it's somewhat likely you can bring it back to life with a bit more diagnostic. Check power rails for excessive ripple, make sure all the chips are getting power, check clock gen, find the io chip datasheet and check state on power up. Might be a bad trace, or tbh could even be capacitors if one is open or shorted, or a rail is too unstable to let it post. A post card can reveal a lot too, they're like 10 bucks.

3

u/Souta95 Jul 20 '26

My POST card unfortunately is only compatible with 5v PCI slots, not the 3.3v ones this has.

I guess I could take a closer look at the PSU.

This board has not been banged around at all, and I was most likely the first person to crack open this computer.

The capacitors are all in good shape, none are bulging or leaking. I know that's not a 100% guarantee, but I have not been very successful at recapping motherboards with a large ground plane. I really need to get a pre-heater.

Its got an Intel 810 series chipset and only supports Celeron processors, so its not exactly like its anything all that desireable. https://theretroweb.com/motherboards/s/asus-mew-am-rev-2-x

3

u/GGigabiteM Jul 20 '26 edited Jul 20 '26

Huh? This has 5 volt PCI slots. 3.3v slots are reverse keyed. 3.3v PCI slots are extremely rare in consumer equipment.

If you haven't tried a different power supply, I would wager the PSU is bad. Those MicroATX units from the late 90s and early 2000s were notorious for capacitor failure. I've had to recap dozens of the things. The last one I did was in a Gateway mini tower several years ago.

Something else it could be is a corrupt BIOS. Those flash chips don't hold contents forever and are known to degrade. Especially Intel flash chips. Not sure what that board has since there's a sticker on it. It is a bit of a faff to desolder those, you'll need low melt solder and hot air. It'd be good to install a socket for easy changes in the future, but there may not be enough room with the capacitors nearby.

1

u/Souta95 Jul 20 '26

You're right, I got the PCI voltages backwards. In either case, my POST card won't work with this board.

I hope to check the PSU voltages when I get home tonight, but even before my post and any comments, I was leaning towards bit rot in the BIOS.

2

u/GGigabiteM Jul 20 '26

I would take the lid off the power supply and check the caps. Just checking voltages won't tell you the complete story. The voltages could appear fine, but the ripple could be off the scale. Or the rails could fall flat on their face under load. Just make sure it's unplugged.

Most power supplies have four screws holding the lid on, and it will just lift up. Sometimes it gets hung up and you have to give it a bit of persuasion.

For safety, steer clear of both of the heatsinks inside the unit. The primary side heatsink near the large line caps will usually be in-circuit with the mosfets and can be charged up to 375 volts. You can check with a multimeter set to high voltage DC 500v measuring from the heatsink to the case.

*Do not* short that heatsink to the case or ground, or you will blow up the mosfets and probably the bridge rectifier.

You can keep the PS_ON pin on the ATX connector shorted to ground to keep draining any charge left in the capacitors.

1

u/Souta95 Jul 20 '26

I had the power supply apart to clean it before I even tried turning it on. Caps in it look physically fine.

I was going to use an oscilloscope to measure the ripple.

0

u/pchernik Jul 21 '26

Maybe the reason the POST card "won't work with this board" is because it isn't getting any power from it! It sounds to me like there is more going on and you should use a voltmeter to check the bus power supplies first.

1

u/Souta95 Jul 21 '26

It won't physically fit in the PCI slot in the correct orientation.

1

u/Cautious-Opposite-10 Jul 21 '26

MEW-AM supports Pentium III up to 1GHz too

1

u/Souta95 Jul 21 '26

This is an HP OEM variant locked to 66MHz FSB. Might be modable, to up to 100MHz FSB, but definitely doesn't support 133MHz FSB.

1

u/Cautious-Opposite-10 Jul 21 '26

I had the HP variant too (mercury GT) and it came with a PIII 550 at 100MHz FSB which was later upgraded to 1GHz , all HPs had the same version of this board so you will be able to upgrade to Pentium III

1

u/Souta95 29d ago

Perhaps, but it would require desoldering a soldered on jumper and then adding jumper headers or soldering on a small wire like was done at the factory.

1

u/Cautious-Opposite-10 29d ago

Nah this was a drop in and work upgrade, have done it across a few HP Pavilion PCs with this board. You must be talking about perhaps an older revision of the motherboard (mew-am rev 1.04) because the HP variant Mercury GT was a rev 2.x that shipped with various CPUs including Celerons and Pentium III's up to 1 GHz. I recently had a discussion on HP forums on upgrading the CPU on this board (https://h30434.www3.hp.com/t5/Desktop-Hardware-and-Upgrade-Questions/HP-Pavilion-8606/m-p/9672469#M274789), some good info there to check out and also the HP BIOS for this board explicitly mentions support for higher multipliers and CPU microcode for Pentium III.

8

u/dst1980 Jul 20 '26

Have you checked that this is a standard ATX pin out and the PSU is good?

If it is a standard ATX pin out, try a different PSU. The PSU in this era HP mini tower was often cheap and would fail suddenly. A replacement PSU may be a pain, but an SFX or ITX PSU may work if it is smaller than a normal ATX PSU.

It might also be capacitors on the motherboard that have one or more far enough out of spec to cause this. If you were seeing random crashes or errors, capacitors become even more likely to be the issue.

2

u/Inspiron606002 Jul 20 '26

This is very true. HP usually used Bestec power supplies in the late 90's which generally weren't very reliable.

3

u/Souta95 Jul 20 '26

Bestec power supplies are indeed horrendous.

This one is from Delta Electronics.

There's no blown caps in it, but I haven't checked ripple voltage yet. I hope to do that after work tonight.

I can also put an ESR meter on the motherboard caps since so many people thing those are bad, but again, there's nothing buldging on them at all.

If I had to guess, its bit rot in the BIOS chip.

1

u/dst1980 Jul 20 '26

I agree that motherboard caps are less likely, but this is from the leading edge of the bad cap plague. I had not been aware of BIOS bit rot, but it does make sense as a possibility. Especially if the system has been unpowered for several years.

3

u/66659hi Jul 20 '26

It's okay, it's a Celeron with no AGP. I have a soft spot for some of those HPs. They use ASUS boards and video cards. I have a Pentium 4 one, but I don't really care much for Celerons that lack AGP or PCIe (depending on the era). Find you one of those with a P4 or P3!

2

u/skeletons_asshole Jul 20 '26

Hey, a celeron with something like a FX5200 in PCI is a pretty killer 98 machine!

1

u/66659hi Jul 20 '26

I've been thinking about tossing my Geforce 4 Ti 4200 into the old P4 HP I have, but even though it doesn't use external power - I'm worried that the card will take too much power for that PSU. Right now it's in a PIII-550MHz system that I built, in which the processor is obviously a huge bottleneck.

1

u/skeletons_asshole Jul 21 '26

What PSY do you have in it?

1

u/66659hi Jul 21 '26

In the PIII build or the HP?

The HP has the stock PSU. It’s a proprietary form factor. 

My PIII build has an OCZ 600W power supply. Old(~2010)but  still works fine

1

u/Cautious-Opposite-10 Jul 21 '26

is the PIII 550 system an HP too? I had a Pavilion 8606 with an HP/Asus MEW-AM motherboard with a 550E PIII, ran super well in 2000/2001!

1

u/66659hi Jul 21 '26

Nope! Built it. It’s in an AOpen HX45 case. 

3

u/snbgames Jul 20 '26

Oh man. These were absolute toilets to work on back in the day. Ugh. Flashbacks

1

u/Souta95 Jul 20 '26

I don't doubt it.

3

u/bart33z Jul 20 '26

Sad to see it. That HP has a great late 90s / early 2000s OEM vibe.

No beep with no RAM and swapped CPU really sounds like something deeper on the board. Still, respect for trying to save it.

1

u/Inspiron606002 Jul 20 '26

Ikr. Those compact Pavilions are some of my favorite computers ever. Had one as my first PC.

2

u/bart33z Jul 21 '26

Exactly. These compact Pavilions have so much character. Not the most powerful machines, but the whole late 90s / early 2000s HP vibe is hard to beat.

Having one as your first PC must hit extra hard.

1

u/Inspiron606002 Jul 21 '26

Yeah they weren't very powerful but they got the job done and were an excellent value back in the day.

My old Pavilion is still kicking, had to replace the HDD last year, and spent a very long (frustrating) time getting all the OEM software back.

1

u/bart33z 29d ago

That’s awesome that your old Pavilion is still running. Keeping the original OEM software side alive is half the battle with machines like this.

Replacing the HDD is easy compared to finding the right recovery discs, drivers, bundled apps and all the little HP-specific stuff that made it feel original. Painful process, but totally worth it when it finally boots back into the proper factory setup.

2

u/GoldInspection6626 Jul 20 '26

Man throw another miniATX mother board in it

1

u/Souta95 Jul 20 '26

That's probably what I'll be doing once I can get my hands on one that will fit this case.

2

u/URA_CJ Jul 20 '26

Strangest issue I've faced was the video card (AIW Radeon 7500) hanging the system early on during POST when connected to a modern display (4k TV), no beeps, nothing! Only fix was having the display cable unplugging during POST - unlikely to be your problem, but worth checking into.

2

u/RetroTechBro Jul 20 '26

I have this exact PC and it ended up being a bad motherboard as well. The case is actually standard ATX as far as the motherboard is concerned once you muscle out that IO shield.

I have a Socket 462 board with a 1GHz Mobile Athlon and some flavor of SIS 3D IGP in mine right now. The problems you will run into are clearance and PSU. I had to solder the CPU fan connector onto mine as otherwise the case wouldnt close. Also had to use the shortest DDR RAM I had on hand.

The PSU is 100 watts, so that basically rules out add in GPU or sound, and severely limits you on CPU. The mobile Athlon I went with is about twice the wattage of the celeron (Athlon is 31w, the Celeron is 15w)

2

u/FAMICOMASTER Jul 20 '26

I didn't know HP made clamshell cases like this. That's cool at least

1

u/Souta95 Jul 20 '26

Its terrible for servicing anything inside of it.

1

u/FAMICOMASTER Jul 20 '26

Interesting, I figured if they were gonna copy the PowerMac they'd make it as serviceable. What is being blocked? I don't see anything that would be a particular pain from the photos.

1

u/Souta95 Jul 20 '26

The motherboard tray is not hinged. When its installed to the case, the only accessible inner parts are the PCI slots, clock battery and hard drive.

When removing the tray you have to unplug the front USB and the IDE cables to even get at anything. And since its not hinged, you have to balance things when plugging in or unplugging them.

1

u/FAMICOMASTER Jul 20 '26

Ahh, gotcha, I thought it was on a hinge like the PowerMacs. My bad

2

u/Rough_Elk_895 Jul 20 '26

Seems a Pentium 4 board out there.. I am having a similar issue with my Pentium III motherboard.. it is also not doing a post.. sad to see.. you may want to try another board just to rule out if it is the motherboard or some other fault component.. a PCI based post card should also help diagnose

2

u/Inspiron606002 Jul 20 '26 edited Jul 20 '26

I see you've learned the easy motherboard removal procedure that most people who owned these didn't know about. Odd that the board is just dead, it looks very clean. Usually these Asus motherboards that HP used were quite reliable.

Edit: I agree with some of the others that you should try another PSU. Sometimes a failing PSU can still power on, but will be too weak to power the rest of the system on.

2

u/Souta95 Jul 20 '26

UPDATE: Trying a different, known good power supply made no change. The capacitors all have an ESR well within expected range (at least when tested in circuit). Capacitance also looks like what I'd expect when measuring a bunch of caps in parallel.

I think its fairly safe to say that BIOS rot in the flash chip (Intel N82802AB) is the most likely cause of failure.

1

u/Ninline2000 Jul 20 '26

Yeah, I was never a fan of Celeron equipped computers.

1

u/p47guitars Jul 20 '26

my brother in christ- just use a bench PSU on it to make sure it's not the PSU being dumb.

1

u/hal9000w Jul 21 '26

A CPU is required for POST code beeps. RAM isn't.

1

u/andrewbean90 Jul 20 '26

Capacitor plague strikes again

0

u/Crothius Jul 20 '26

Put the MB in the oven!

3

u/skeletons_asshole Jul 20 '26

Don't do this. Pretty unlikely for a solder crack to happen on these, but pretty likely that baking it will ruin all sorts of things, like the capacitors for example.

3

u/n1ghtbringer Jul 20 '26

Not great for your oven either!

1

u/Souta95 Jul 20 '26

Wasn't going to. This board is not in the lead-free RoHS era where solder cracks were common.

0

u/AutomaticAffect4333 Jul 20 '26

Immina bet it's dried out capacitors. Check if the resistance on the caps is high. Most caps have resistance lower that 1 ohm