powering ql via expansion connector ?

[fuasn]

Hi,
I'd like to ask if anyone knows if the QL could be fully powered via the 64pin expansion connector. I've tried to apply 9V on VIN and the QL boots up into minerva.

The Service Manual says:

>8.1 A custom-built power pack, external to the main board, supplies 9 volts d.c. at 2 amps and 44 volts peak-to-peak a.c. to the board input on connector J3. The power pack uses a thyristor to limit peak voltages on the d.c., but is otherwise unregulated and has significant ripple.
>8.2 The a.c. input is applied to two rectifiers IC37 and IC36 to produce +12 volts at 80 milliamps and -12 volts at 50 milliamps, respectively.
>8.3 The d.c. input is regulated down to +5 volts by regulator IC35.
>8.4 All three supplies are completely protected in that the regulators are equipped with thermal and short circuit shutdown.


I assume that +12V and -12V are VM12 and VP12 on the connector. Does anyone know if applying +12V DC to VP12 and -12V DC to VM12 on the connector would do any harm for the thyristors mentioned (or anything else) and would it provide everything (e.g. microdrives) with the required power / voltage ?

[tofro]

I assume that +12V and -12V are VM12 and VP12 on the connector. Does anyone know if applying +12V DC to VP12 and -12V DC to VM12 on the connector would do any harm for the thyristors mentioned (or anything else) and would it provide everything (e.g. microdrives) with the required power / voltage ?

feeding these voltages from the expansion connector shouldn't be a problem. The mentioned thyristors are located in the PSU (that you wouldn't have connected, I suppose), not on the QL main board. In the past, people have placed QL boards in PC cases and supplied them externally with voltages from PC PSUs, no harm done.

The "anything" question: The microdrive circuit boards are powered by 5Volts DC that are created by their own regulators on the mdv subassemblies from the 9V Vin. If you don't feed the QL with 9Volts DC, microdrives will likely not work.

And, obviously, you'll also need to supply 5Volts to the QL as well, but I think that's a given.

[fuasn]

thx,
if i provide 9V on VIN, the 7805 in the QL should generate the 5V, not ?

as said, i also tested that, providing 9V to VIN and the QL booted fine into minerva

[tofro]

thx,
if i provide 9V on VIN, the 7805 in the QL should generate the 5V, not ?

as said, i also tested that, providing 9V to VIN and the QL booted fine into minerva

As said above: You need to supply (5V DC, 9V DC AND (+-12V DC OR 15VAC))

[RalfR]

-12V for SER?

[Pr0f]

The 9v on the edge connector will feed the regulator with 9V - but that's a long circuit path and was originally specified to provide 9V on the edge connector for plugin cards - maybe allowing 500ma of current to expansion cards with their own regulator. It was not designed to feed 9V to power the QL itself.

Regarding feeding the VP12 and VM12 lines with + and - 12v - this would connect the 12V to a small 100ma Regulator chip's output, with no power on the inpuit - you should check if these regulators can handle that conditon. There is no information in the standard data sheet that specifies the handling of this condition.

[Pr0f]

It's common in power supplies to see a Diode across the regulator to prevent such voltages damaging the regulator - they are NOT present in the QL circuit.

More details are here:

https://forum.arduino.cc/t/why-to-uses- ... or/1052410

[Peter]

I assume that +12V and -12V are VM12 and VP12 on the connector. Does anyone know if applying +12V DC to VP12 and -12V DC to VM12 on the connector would do any harm for the thyristors mentioned (or anything else) and would it provide everything (e.g. microdrives) with the required power / voltage ?

Doing this from the expansion port applies voltage to the output of the QL's 7812 and 7912 regulators, while their input is somewhere around 0V. This would result in Collector-Emitter voltages with wrong polarity inside those regulators. I would not do that. If the +/- 12 V regulators are removed from the QL, no problem.