Vertical collapse on Storage System portable PC

I recently stumbled across a junked ‘Picollo’ portable PC made by Storage System Inc. This unit had a 66MHz 486 Overdrive processor and 10″ Sony Trinitron SVGA display and no doubt cost a fortune in its time.

Unfortunately the chassis had been partly gutted, missing the outer case and a variety of parts. The 10″ monitor still appeared to be salvageable however so I gave it a try.

After connecting everything as it appeared to go I connected a PC and powered on the display. Sadly the it was completely collapsed vertically, although I could make out enough detail in the thin line that appeared to be sure that it was otherwise functional.

The deflection is handled by the board mounted on top of the CRT. After fixing loads of dry joints around the horizontal output stage I decided to focus efforts around the vertical deflection stage.

This is based around an ST TDA1675A IC. I grabbed the datasheet for the IC and discovered that the circuit in the display was quite similar to the test circuit shown in the data sheet. The scope confirmed that the sync input was working, as well as the ramp generator. Unfortunately there was no output.

Google searching for the IC revealed many forum posts identifying this as a common cause of failure, and that it was also sensitive to failed components elsewhere in the vertical deflection circuit. Many people suggested replacing all of the surrounding capacitors and diodes as well as the IC just as a precaution.

TradeTech listed the IC as being on back order which was not ideal. In the mean time I though it would be worth attacking the other likely culprits in case the IC was still OK.

I replaced all of the electrolytics in the vertical stage as a matter of course but it didn’t fix the problem. I also identified a Zener diode (ZD201) with the marking ‘4A3’. After some research I found that this is in fact an HZ4A3, a 3.7V Zener. The closest I could get was a 3.6V 1N4729 so fitted one just in case. No difference.

There was also a standard 1N4004 rectifier diode (D207) mounted under the heatsink. I replaced this and it immediately fixed the problem! The weird part is that the diode appeared to check OK out of the circuit.

The horizontal yoke connector also had some discolouration on the plug due to heating because of a bad connection. I cleaned up the pins in the connector the the PCB header before reassembling it.

So now I have a dinky vintage 10″ Sony Trinitron SVGA display and just need to find a use for it! 🙂

Multiplexing 7 segment LED displays with Arduino

Here’s an example on multiplexing three seven-segment LED displays from an Arduino using a single 4511 IC and a handful of transistors. This builds on my last post about interfacing to a single display

Multiplexed displays in action

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Making PCBs

Here’s a brilliantly simple article on making PCBs at home.

I’ve tried a few times with the toner transfer method but using magazine paper looks to be very effective.

Brother HL-2150N in Ubuntu Karmic

Normally I try to stick with HP printers when using them in Linux as they seem to have the best support thanks to HP’s efforts with HPLIP.

I recently went against my own advice and purchased a Brother HL-2150N monochrome network laser printer. Brother have at least tried to provide drivers for Linux and even supply Deb packages. Unfortunately installation is a mess involving ugly binary wrappers and packages that don’t appear to conform to Debian policies very well.

Whilst there is no official support for this printer model in Ubuntu 9.10, it can be set up to work via Ethernet fairly easily. Read more of this post

Flash drive fakes

Against my recommendation a relative recently bought a 32GB USB flash drive off Trade Me. It cost something like $85 when such drives are currently about $130 at wholesale rates. Read more of this post

Simple Arduino 7 segment display example

It appears that there are many different ways to interface a seven segment LED display to the Arduino; the humble 4511, 74HC595 shift register and a multitude of fancy (and expensive) serial ICs such as the MAX7219.

I decided to use a 4511 driver IC for this purpose as it was the only suitable chip I had lying around. It saves a few pins over driving the display directly from the Arduino and also works from a wider voltage range so can be used for driving large display modules.

LED display in action

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