QL PSU Voltages

[t0nyt]

I decided to test my spare QL PSU with my meter before I try plugging it into a QL, in case I need it sometime

But I’m getting 11v DC and 17v AC, does this seem ok to use please?

Many thanks

[Chris_68]

Hi

Slightly high at least compared to the one I have which is closer to 10v DC and 15.5 V AC.

The voltages are regulated down anyway so I can’t see a problem. Measure them when connected to QL as well.

/Chris

[1024MAK]

The off load voltages are misleading. The PSU is not regulated, so the voltages will be higher than you expect when not supplying the full rated current.

Mark

[t0nyt]

Thanks all

I woke up during the night and realised I hadn’t done the obvious thing of comparing the values to the PSU I’m actually using…

Anyway have now done that and they are around 11.1 dc & 16.8 ac. So pretty much the same

Will risk plugging it in, but seems like it should be ok

Many thanks

[t0nyt]

Could I ask where I should check the voltages inside the QL please?

Would like to double-check the spare PSU and I also have an issue with a vRetro PSU I’d rather be using so need to check that too

Many thanks

[tofro]

Could I ask where I should check the voltages inside the QL please?

Would like to double-check the spare PSU and I also have an issue with a vRetro PSU I’d rather be using so need to check that too

No real need to. There is a set of very reliable voltage regulators in the QL that either spit out the correct voltages or none at all. What you should observe a bit with an unknown PSU is excessive heat. The rather outdated regulation circuits in the QL basically transform whatever comes into the QL that is too much for its circuitry into heat and dissipate it into the air.

If you absolutly want to, the following table from he service manual shows where to measure and what the acceptable limits are.

[t0nyt]

Thanks Tofro, but I don’t know much about this kind of stuff

I assume I put the red probe as per the chart, but do I use a single ground point for the black probe please?

Many thanks

[Pr0f]

Yes - if using a multimeter - put the black lead on ground - a good place that's convenient is the modulator housing, and then use the red probe to take your readings - but if the voltage you are measuring is AC - then you will need to switch the multimeter to AC range for that reading. You will get erroneous readings if you leave it in AC mode to measure the DC voltages.

[Pr0f]

But the input to the 5V regulator should be about 9V DC I always thought (and have measured - when the QL is on). The regulator will work if the voltage is about 1-1.5V above the output voltage of 5V.

[tofro]

Thanks Tofro, but I don’t know much about this kind of stuff

I assume I put the red probe as per the chart, but do I use a single ground point for the black probe please?

Many thanks

Because you need to ask: Don't accidentally connect pins when you set the probes, they need to go where indicated and exactly there, or you may fry important components. If you feel unsure, refer to the first sentence of my answer, and if the QL seems to work, there's actually no need to fiddle with it, there's nothing to gain from it.