Re: HP DC5100 mobo

On 7/11/24 01:36, Paul wrote:
> On 7/10/2024 10:48 PM, philo wrote:
>> Found a P-IV mobo in my workshop and built a machine ideal for fooling around with older operating systems. Original case long gone so I'm trying to figure out the headers.
>>
>> On bootup I get a message that front panel USB and sound not present and I have to hit F1 to continue, There is no BIOS option to ignore faults.
>>
>>
>> I Googled and found out that in the wiring harness, there would have been a jumper and all one need do, to avoid the error is to jump the pins.
>>
>> Unfortunately I have not seen any tutorial which covers my specific machine and there indeed are many variations.
>>
>> The audio and USB headers are apparently normal but there is one 16 (15) pin header that evidentiary is the one I need.  The on-line help I've found just shows the model with a 20 (19) pin header.
>>
>> The manual does not give specifics.
>>
>> If anyone here knows, please let me know,
>>
>> Obviously this is hardly important.
> 
> 1         MIC          Front panel microphone input signal (biased when supporting stereo microphone)
> 2         AUD_GND      Ground used by analog audio circuits
> 3         MIC_BIAS     Microphone power / additional MIC input for stereo microphone support
> 4         AUD_GND      Ground used by analog audio circuits
> 5         FP_OUT_R     Right channel audio signal to front panel (headphone drive capable)
> 6         FP_RETURN_R  Right channel audio signal return from front panel (when headphones unplugged)
> 7         AUD_5V       Filtered +5 V used by analog audio circuits
> 8         KEY          No pin
> 9         FP_OUT_L     Left channel audio signal to front panel (headphone drive capable)
> 10        FP_RETURN_L  Left channel audio signal return from front panel (when headphones unplugged)
> 
> When there is no AC'97 sound header going to the computer case front,
> the motherboard comes from the factory with two blue jumpers
> from 5-6 and 9-10. You remove the blue jumpers and install
> the ten pin FP cable onto the 2x5 header pins (making sure the pin 8
> key aligns with the cable). Because there is a 5V supply on that
> cable, you don't want to short out that pin.
> 
> We no longer find two blue jumpers today, because the motherboards
> use HDAudio standard instead, and the audio chip has LineOut for
> the back of the computer and HeadPhone for the front of the computer
> and there is no need for thru-wiring.
> 
> But if you go back far enough, there were two jumpers. On a
> machine like an HP or a Dell, the front panel cable would already
> be fitted, and they would not put the two blue jumpers in a tiny
> baggy for you.
> 
> It's hard to say, in your case, why there would be a sensing function
> to see if the front panel cable has fallen off. The only pins they can
> use for "tricks", are pin 2 and pin 4. While normally they would both
> be hard grounds, an engineer could make one a logic input and make
> the other a hard ground, and then arrange the front panel header/microphone
> PCB to make continuity between pin 2 and pin 4 wires. This would allow
> sensing whether the cable was in place or not. Retail motherboards
> do not do such a thing. Never seen it. But that's the only facility I
> can see on the header, that can be re-purposed. Anyone making a headphone/microphone
> PCB for the front of the computer, should be joining pin 2 to pin 4 on the PCB>
> 
> The 5V pin on that cable, it may be used to power a 2 watt amplifier
> on the far end of the cable. I don't know if the practice is
> to fit a Polyfuse for that pin, on the motherboard. I can tell
> you that the 1x4 SPKR for the beep function on a PC, that has NO fuse,
> and some manuals warn that if the "red wire gets jammed in the door,
> the red wire may melt or smoke". Similarly, the +12V on the fan headers
> is not protected by a fuse, and overloading a fan header (past the
> crude value listed in the manual), can burn out the fan power track.
> This means the motherboard PCB designer has used a 25 thou track
> on purpose for the fan headers, ensuring the track burns out if
> you short it. Ruining the motherboard is cheaper than fitting a fuse.
> 
> The absolute cheapest piece of work I saw, some joker used a single
> Polyfuse for the entire motherboard. All the 5V draw for auxiliary functions
> flowed through one fuse. The parallel port 5V, the PS/2 keyboard and mouse,
> all the USB ports, all flowed through one Polyfuse. You're not supposed
> to do that. Mainly, because the users will experience functional outages
> on their board, and won't be able to figure out the pattern as to what
> is doing it :-) Typical motherboards have at least four or five Polyfuses,
> but there are some things (like SPKR), they just "let her smoke".
> 
> *******
> 
> The USB wiring for USB2 (from that era), is like this.
> 
>     VCC    VCC   \
>     D+     D+     \___ There are enough contacts to wire the four
>     D-     D-     /    pins on each USB2 black connector. A 2x5 is
>     GND    GND   /     enough for a stack-of-two USB2 connectors.
>    SGND             <=== This is a shield ground for the outside of the cable
> 
> There are enough grounds there, you could arrange one of them to function as a sensor.
> 
> Again, there is no need to sense whether the cable is present or not.
> Nothing bad happens if a front panel USB2 cable assembly like that, falls off.
> 
> At one time, there were *different* pinouts for USB2. They were not
> all the same. Not much later, they settled on one wiring diagram
> (as far as I know). However, some older stuff, you may find some
> differences. Sometimes a manual would admit what the wiring was,
> but not always. A similar kind of thing happened to the USB3 2x10
> header, which is used for fitting two USB3 onto the front of a PC.
> The 10 pins are sufficient for the 9 contact USB3 plus 1 shield ground.
> The 2x10 is sufficient for two USB3 on the front panel.
> 
> They have added other, higher quality connectors for front panel USB
> since then. Since I never seem to own the proper cable for those,
> I'm not the least interested in what they are :-) Some day there
> will be a Thunderbird or a Thunderbolt or a USB4, and I still won't care :-)
> I'm funny that way.
> 
> Summary: I don't know the answer to your question, but perhaps a bit of
>           detective work with your multimeter set to "volts" with respect
>           to chassis ground, will help you figure out how they have rigged
>           a sensing function. For example, on the audio, with PC running,
>           if pin2 or pin4 are riding pretty close to +5V, then the pin
>           is likely a logic input instead of the analog ground the standard intends.
>           You will have to use your electrical craft to figure it out,
>           what they've done as a "trick".
> 
>           The shield ground and the logic ground should all go to the same
>           place, and in some cases, the shield ground receives ESD discharges
>           in that wire. That would be a lousy place to be fitting a logic input
>           for a cable sensor. ESD discharges into a front panel ground, not only
>           can upset what is at the other end of the cable, just the inductive
>           coupling between tracks can couple the transient into adjacent signals.
>           This is one reason you have to think about whether wiring front panel
>           USB is a good idea or not (the fascia can be plastic and floating and
>           the cable becomes the discharge path).
> 
>     Paul



Thanks Paul, problem is my mobo has a 16 pin header.

I have found no documentation for that one.

I think I'm just going to leave it alone as the pause ...in a way ...can 
be helpful if I want to get into the BIOS