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Pentium Overdrive PODP5V83 - Detected as Pentium 33 and underperforming - Compaq Deskpro XE

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First post, by nelizmastr

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Hi Vogons members,

I have an interesting issue regarding my 486 based COMPAQ DESKPRO XE system.
Originally the system was an XE 466 with a DX2-66 installed. I've since swapped it for a DX4 Overdrive 100MHz.
Very recently I got my hands on a Pentium Overdrive 83MHz which exhibits some very erratic behaviour and
very much underperforms.

Full system specs for the record:

- DESKPRO XE Socket 2 mainboard
- 16MB 70ns memory
- 256KB cache
- 3.2GB Quantum Fireball HDD
- CD-ROM drive
- Primax Soundstorm (GUS clone)
- SB Vibra 16 PnP
- 3Com Etherlink III
- Onboard VLB QVision 1024 1MB video

OS is DOS 6.22 with WfW 3.11.

What I've noticed, in numbers:

- Software reports the CPU as a Pentium 33. BIOS reports Pentium 66
- Quake at 320x200 runs at 9.1fps on the Pentium, 10.2fps on the DX4
- Chris' 3D bench runs at 28fps on the Pentium, 43fps on the DX4
- 3DBench 1.0 runs at 34fps on the Pentium, 59fps on the Dx4

The only way of controlling CPU settings on this system is the SW500 jumper block.
This block consists of 4 switches.

SW4 sets the FSB to 25MHz or 33MHz the others are for the rest.

The following settings were applied for testing:

DX4:
1:ON
2:OFF
3:ON
4:OFF

POD:
1:OFF
2:ON
3:ON
4:OFF

Things I've tried so far:

Any other jumper setting will prompt an incorrect CPU setting message at POST, so they are correctly set.
CPU pins were cleaned
Socket was cleaned
CMOS cleared
CPU reseated
BIOS was updated to the latest available version 31/10/94.
I've confirmed that the L1 cache is detected in write-through mode so that should be working.

Are there perhaps people on here that have experience with this system and know some tricks or something I can try?
Again, hardware and BIOS wise, there is basically no control, so perhaps there is some software hack?

P.S. I don't have any other 486 boards to try, the next best thing I have is socket 7 sadly.

Pulling my hair out over this 🤣. Thanks in advance to your input!

Reply 2 of 7, by zapbuzz

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Socket3 wrote on 2022-04-21, 19:18:

Make sure the fan on the pentium overdrive CPU works. If it doesn't, the POD will run at 1x multiplier (it's a failsafe), witch would explain your scores and the fact that it's detected at 33Mhz.

I agree but i'd still check the capacitors as even if they're not bulging at such old age a few would have surely dried out because electrolyte eventually vanishes a phenomenon even with disposable batteries of which elecrolyte capacitors are relatives.

Reply 3 of 7, by nelizmastr

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Socket3 wrote on 2022-04-21, 19:18:

Make sure the fan on the pentium overdrive CPU works. If it doesn't, the POD will run at 1x multiplier (it's a failsafe), witch would explain your scores and the fact that it's detected at 33Mhz.

That must be it! Mine came without the fan. Isn’t there something I can do about that? I added my own fan that doesn’t connect to it in any way, but would still adequately cool it.

Reply 5 of 7, by nelizmastr

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Babasha wrote on 2022-04-21, 19:30:

You should short some contacts on processor ceramic to override it to 2,5 multiplier.

From what I gather the three gold contacts on the ceramic are for the fan.

Granted I have no soldering equipment, what are my options? I do have a multimeter though.

Reply 6 of 7, by Babasha

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nelizmastr wrote on 2022-04-21, 19:37:
Babasha wrote on 2022-04-21, 19:30:

You should short some contacts on processor ceramic to override it to 2,5 multiplier.

From what I gather the three gold contacts on the ceramic are for the fan.

Granted I have no soldering equipment, what are my options? I do have a multimeter though.

Just short like on this picture.

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Need help? Begin with photo and model of your hardware 😉

Reply 7 of 7, by nelizmastr

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Babasha wrote on 2022-04-21, 19:53:
nelizmastr wrote on 2022-04-21, 19:37:
Babasha wrote on 2022-04-21, 19:30:

You should short some contacts on processor ceramic to override it to 2,5 multiplier.

From what I gather the three gold contacts on the ceramic are for the fan.

Granted I have no soldering equipment, what are my options? I do have a multimeter though.

Just short like on this picture.

Worked like a charm! I shorted them using a pencil as a proof of concept and it’s running properly now. Time to make the mod and cooling setup more permanent. Thanks a lot for your help!

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