today we talk about the system to powering our beloved BBQL, in case we have lost the original power
supply or we never had it!
Before we go into this article is needed to say that making a new power supply is a job for people that have
some knowledge about electronic and electrotechnic and some manuality in use of tin welder; it’s for Do-It-
The original QL machine is an electronic device that use low voltage power supply so we need to start from
domestic power line that in europe has a 220 volt a.c. value ( means that it change its own polarity every
1/50th second) and drop it to the lower value and also change it to a continuous polarity (one wire positive
and the other one negative); our QL need also a third wire that bring an alternate tension of 15 volt.
The primary 9 volt voltage is furthermore lowered to the value of 5 volt that is the main rail for all
integrated circuits of main board, it is also the main power line for the expansion connector on the left side
of QL; the 15 alternate voltage is used to obtain the -12 and +12 volt for serial ports and also the +12 volt to
powering the video circuitry. It’s not possible to power the QL with only 9 volt because the main
intergrated circuit of video output (the MC1377P) need 12 volt d.c. to work fine.
The simple power supply for QL is same as picture below:
The electronic parts for that schema are easy to find even on Amazon and these are the links:
TR1 is a transformer with primary 220v a.c. and secondary of 15v a.c.:
B1 is a rectifier bridge that change the a.c. to d.c. voltage together with condensators C1 and C2: rectifier
bridge KBU1010 https://www.amazon.it/dp/B0725VPYYB/ref=cm_sw_em_r_mt_dp_U_7XpMCbVA5W0MJ;
the condensator C1 has value of 4700 microFarad, C2 has value of 100 nanoFarad
IC1 is a voltage regulator that drop the power voltage to the right value for the input plug of QL, 9 volt; it
can be a modern switching regulator as this:
https://www.amazon.it/dp/B01B7BQZJK/ref=cm_sw_em_r_mt_dp_U_LZpMCbAPA89KR; or we can use a
linear regulator IC the classic L7809 in TO-3 case to have more current
C3 is a output rail capacitor that help the line to remain stable.
Other problem to solve is the plug for the QL power socket: we can use with a good result, the connector of
a CPU heatsink fan!
In effect the fan of a lot of heatsink used into desktop PC has a 3 pin connector that we can adapt to inset
into power socket of QL:
This picture can display how can we do:
After some work onto the plug, it easily insert the QL power socket in the right manner !
To more info the 3 pins are identified as:
1- further to the left : 15v a.c.
2- mid: common ground
3- further to the right: 9 volt d.c.
the max current that we can have from a original power supply is about 2 amps, with our schema and
components listed we can have more than that, about 3 amps; the max cost will be of 30 euro and the most
expensive component is the trasformer, so if we are lucky to find it in some way….
We hope that these infos are useful for all people that wants to revive a QL without power supply and
enjoy with it for a long time!