IBM Netvista 6790 - not booting

[carlitosbala]

Hi All,
I'm new in BadCaps, so I hope this is the right forum to make my question.

I come here because I have an IBM NetVista 6790 that doesn't boot.

I have always liked to tinker with PCs but only recently started trying to get into component repair, so I know how to check a PC but I'm at a loss without schematics on what to check when things are not obvious (i.e. a shorted mosfet). Also, I am sure there are a lot of symptoms that for someone experienced will point directly to the issue, but I don't know how to identify.

So this machine doesn't boot, and by that I mean:
- When using the power button, it starts the CPU fan
- It can be shut down with the button after 6 seconds
- the CPU doesn't get hot (which is quite an achievement for a P4...)
- RAM voltage looks OK (3.3 V)

There are no ICs getting hot, nor any kind of damage in traces or components. The capacitors *look* ok, none of them is obviously damaged.

I changed the battery in case that would be part of the problem. I also checked the power mosfets with my multimeter.
- for three out of four CPUS I have, I got a correct reading (1.8 V)
- for the other, a P4, I got 1.4 V

I actually kept checking and noticed the voltage in the mosfets was not stable: instead it took like a minute after the board was turned on to get to those values (slowly increasing from around 1V). Does that mean anything?

In summary, what I would like to ask is: what else can I check now?

I'm absolutely aware that this repair doesn't make sense from an economics point of view, but it's a learning experience and also I love the IBM-iness of this machine so I'd really enjoy having it running again.


Thanks in advance

[piernov]

Re: IBM Netvista 6790 - not booting

What are the sSpecs of the CPUs?

[carlitosbala]

Re: IBM Netvista 6790 - not booting

They all come from machines that weren't mine and I don't have a working 478 board, so for all I know they might be dead.

3 of them are Celerons: 1.7/128/400, 1.8/128/400, and 2.4/128/400.

Two are P4s: 2.4GHz/512/800, and 1.8/256/800.

The 1.7 Celeron and the 1.8 P4 also say 1.75V

[piernov]

Re: IBM Netvista 6790 - not booting

It's better to look at the sSpec which reads as SL*** on the CPU, it avoids confusion and also differentiates between steppings and generations which is very important for the Pentium 4 era.

In any case the Pentium 4 will surely not work in this machine as they're FSB 800 and the northbridge supports FSB 400 max.

The first revision of the machine is from 2001 and the spec sheet says "Intel** Pentium** 4 processor with internal clock speed of up to 2 GHz", so most likely it is designed to support only the first generation of Pentium 4, Willamette. Northwood with FSB400 may or may not work, it may or may not require a BIOS update, hard to tell. Later revisions of the machine seem to support Northwood with FSB400 as well at least.

Using a Celeron instead of a Pentium 4 should still work though, so at least the "1.7/128/400" should work, these specs seem to match only with a Willamette one.

With this CPU you should at least get a stable 1.75V or so on CPU VCore. If you don't I'd suspect the PSU and the CPU VCore caps first.
Also check if it beeps without RAM.

[carlitosbala]

Re: IBM Netvista 6790 - not booting

Thanks for the tips. I should have looked at it: I'm ashamed that I thought sSpec was a typo lol

P4
1.8GHz/256/400 1.75V SL5VJ <- I'm quite sure this is the one the machine had, but it has been a while since I dissassembled it.
2.40GHz/512/800 SL6WF

Celeron
2.40GHz/128/400 SL6VU
1.7GHz/128/400/1.75V SL68C
1.80GHz/128/400 SL876

I tried three different PSUs, with the same result. There are no beeps without the RAM.

[piernov]

Re: IBM Netvista 6790 - not booting

Ok SL5VJ is good, it's a Willamette Pentium 4, there was a typo in the previous message since it read "800" instead of "400".

If voltage on CPU VCore is good you should also check the voltages near the northbridge and southbridge. On these old machines they may not be created by a buck converter but by linear regulators instead.
On northbridge you should see a 1.5V rail and a 3.3V rail (should be the same as the RAM one). On the southbridge you should have a 1.8V and two 3.3V rails (one present only when machine is turned on, the other present even when machine is turned off), and the 3V RTC rail.

[carlitosbala]

Re: IBM Netvista 6790 - not booting

Thanks, piernov, for your advice.

I had put the machine in storage before creating this thread, after spending around 6 hours (couple hours each day for a few days) looking at it and trying to find documentation. I set it aside because I have other boards to play with and this one was not fun anymore.

Yesterday night, after your suggestions, I again opened the machine, prepared the board for yet another check with just the power connected, and started checking with my multimeter around the *bridges. I did find the voltages you mentioned, so I turn it off and put the CPU in. Then I flipped the PSU switch, the fan started... and it beeped. For the first time in the months since I have it, it beeped because it didn't have RAM installed.

So in summary: I got the board to work, but I don't know how.

I do not presume the board is 100% ok, but at least it is booting now. Maybe me picking with the multimeter around the chips charged / discharged something, maybe something in the board is not perfectly attached and by moving it I got lucky, no idea. But I'm happy this P4 Netvista now sits along my P3 Vectra

Thanks a lot for your suggestions. Will keep that in mind if any of my other boards of the era that are still in the "see if this one works" box also refuses to play nice


Regards

[piernov]

Re: IBM Netvista 6790 - not booting

It may have been bad contact in the CPU socket or marginal capacitors. They work better when warmed up, and sometimes just applying power for a while helps them "resurrect" a little bit, but they're probably still failing.