New Bus Expander by Wilco

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Bus Expander

How to use it

I want to give you some recommendations of use for the Bus Expander on its second version, but if you find difficult to understand this, please ask Zozo about how to prepare the Bus Expander to work with your classic card expansions.

This card is a modern copy of the Hungarian made Bus Expander designed long ago by Gyula Mészáros, but with a particularity: by default the cards plugged in the slots will feed its +5v from the 7805 regulator fitted in the Bus Expander from pins 4A/B of the connector.

But all the classic Hungarian expansion cards have its own 7805 regulator and they will not work directly, so you have to do a modification on the bottom side of the Bus Expander. The slots come unconnected from +9v on the 33A/B pins of the connector, but there are a selector at the bottom side on every slot to permit this only joining two cooper pads with a drop of tin. Then, the modified slot will be only used for a classic expansion.

Bus Expander bottom side

Previously, you have to solder a DIL row of pins on the EDGE male connector of your classic card expansion. I will distribute the Bus Expansions only fitted with DIL connectors. But there are on the card holes to solder EDGE connectors, not provided by me.

The Enterprise power supply comes on +9v 2Amp or 1,3Amp variants, so, when all the equipment is connected, if you experience undulations on the screen, probably you need to connect a secondary power supply on the Bus Extension auxiliary power connector.

Also, every 7805 regulator can feed up to 1Amp of current, and this can be insufficient to feed the three slots when all of them being populated. This doesn't applies to slots modified for classic expansions as they produce its own +5v. The rear connector also doesn't count, it only feeds from +9v.

To overcome this I recommend to substitute the 7805 regulator that comes installed (the chip with screw and heat sink) with a 2Amp TracoPower regulator(I don`t recommend the 1Amp variant, of similar price):


The chip has the same pinout than the 7805, and I have used it for decades on my Enterprises without problems. This chip works at ambient temperature, is more energy efficient and doesn't burn your fingers...

On this second version of the Bus Expander, holes have been added to fit an array of 4,7K pull ups to the Data bus, to overcome some problems of shadow segments when a Ram expansion or Turbo mode are fitted to the computer. You can see the pads zone near the expansion connector.

Pull-up array holes