Linux on an Intel DG35EC motherboard

Intel DG35EC was (is?) a PC motherboard for Core2 Duo/Quad processor with embedded support for Serial ATA (SATA), PCI Express, Ethernet and USB while still providing support for 3.5" floppy disk drive, IDE hard disks and PCI. Let's not forget PS/2 keyboard and mouse, parallel port and RS-232 (not exposed on the case).

This is probably the last generation of motherboards to support 3.5" FDD, so it is one of the fastest options for a machine that bridges "both worlds". In my case it sits in a minitower case with enough room to swap disks and expansion cards.

It happily boots from FDD, IDE, SATA, USB, network.

Since the primary use of this machine should be to read old disks I preferred to have a form of Linux, to stay away from viruses and have native support for various partition types. The datasheet states that it supports Microsoft Windows.

I booted it with Ubuntu 24 and, even if the MoBo is from 16 years ago, everything worked just fine. I went ahead with installation on a SATA disk. No boot. I've tried every combination of BIOS settings and no, it just sat with a blinking cursor.

Then I plugged an IDE HDD that had Linux on it. Made it the primary boot option and - boom - it booted. So I tried a fresh install on an IDE disk and ... no boot.

In my the experiments to get it boot Linux I had disabled network boot. This switch even broke the boot process of the pre-installed Win7 SATA. WTH!!.

To boot an Intel DG35EC motherboard on Linux my options are (YMMV):

• live CD or USB
• install on HDD but leave bootloader on FDD, USB or CD 
• install on HDD on another computer and move the disk (not tried with a fresh install)
  

Besides this little quirk, it is a fine machine (give it as much DDR2 memory as you can afford, of course). There is "dd" for Windows too which is enough for imaging floppy disks.

Note. I tried forcing the bootloader either on MBR or UEFI and nothing worked. The BIOS does not mention UEFI but it is probably using something very similar as Linux doesn't fall back to MBR.

Note: I tried the same on a DG33BU motherboard and didn't get further, only slower because of the Celeron processor. Most likely all these DG3x motherboards don't support Linux boot after installation.

PABX Excelltel MK-208 recapped

New look for the MK-208

This was an easy fix, on an easy to rework PCB. I replaced the five largest electrolytic capacitors in the MK-208 PABX, even if three of them were still within spec. This 3€(2025) repair restored a crystal clear analog line so the PABX can go into service. I have also drilled free-hand some holes above the 7805 area to let warm air escape.

Phone to phone works. I am after at least one working fax machine and a computer with modem to host the other end. A 1980's BBS will be last.

Electrolytic capacitors in the power supply circuit.

PABX Excelltel MK-208 recap

The (Excelltel) MK-208 PABX (and alike) is a modern local telephone analog exchange for small offices. "Modern" because it was built after 2010, which is strange since plain old PSTN analog phones were already declining in favor of VoIP. "Small offices" because it features up to 2 incoming lines and 8 internal branches. There is a whole series of these PABX with different combinations of incoming vs branches line, and they all fit in the same case. 

MK-208 boards

Why did I buy such a thing? Because I want to be able to recreate an analog telephone line that can ring those old phones, run a BBS, transport a FAX, all natively without passing through VoIP codecs. This is going to be used in a public interactive exhibition. With 8 branches of the MK-208 there can be up to 4 simultaneous calls.

The PABX has a nice case and its weight might induce you to think it is metallic for heatinking purposes. As it will turn out, it's not.

The PABX powers up and the green status LED blinks. This is normal, whereas you would expect a solid light. I connected two phones, they rang and communicated but the line was extremely noisy. No, not the kind of noise caused by a rusty connector. It was a strong hum. Ouch. The hum/noise increased when I picked up the second phone. Ouch ouch. But there is hope: it might be a problem in the internal power supply, even if a poorly designed product would not the THAT bad (and the Internet would be full of bad reviews, which is not).

Let's look inside. The nice heatsink-shaped case is made of plastic, thick, but plastic. The power supply area is easy to locate, with the transformer and the regulator heatsink in good sight. Needless to say, there are three bulging electrolytic capacitors. This unit is 10 years old, it might have been in service non-stop for 8 years. Probably it gets quite hot as there is no fan and the slots for air cooling are very small (to my under experienced eye).

Close-up on failed capacitors.

I will replace the failed capacitors and those that were subject to too much heat. If this fixes the hum, I will also drill holes in the case right above the power supply area to provide a well needed escape to hot air. In between the two I should measure the temperature inside to confirm that extra holes actually help.

 

Motorola MicroTAC GSM battery pinout (incomplete)

A colleague has given me two Motorola GSM phones, a d460 and an International 8700. According to timestamps on the battery packs, they were used in 1998-2001. 

All three battery packs had no output, of course, but helpful + and - signs mark where energy would enter the mobile phone. This allowed me to use an external power supply and confirm the devices work.

Why not trying to recharge their battery packs? These "MicroTAC" battery packs have connections both on the inner side, to the phone, and on the outer side, to the desk charger. I probed around with the multimeter and found the common ground between front and back.

With nothing to loose I set the power supply to 7.2V and started probing around: soon enough the Li-ion battery pack started taking current. What's even better is that it keeps the charge and powers the mobile phone!

For future reference, here is the incomplete pinout for Motorola MicroTAC SNN batteries:

Motorola MicroTAC battery pinout

The pinout depicted in the picture above should apply to these models:

SNN 4027
SNN 4058
SNN 4102
SNN 4132
SNN 4239
SNN 4259
SNN 4263
SNN 4283
SNN 4310
SNN 4314
SNN 4340
SNN 4346
SNN 4383
SNN 4458
SNN 4467
SNN 4612
SNN 4836

As usual, fiddle with these batteries at your own complete risk, even if you know what you are doing.