Mosfet alternative

[nightmonkeyii]

Hi everyone!

first time post in the lynx section. I had a lynx back in the day, and have just recently re aquired a lynx ii. It still works, but i am about to futureproof it (just bought the caps, all panasonic)

i was wondering if i can use this as a replacement for q12? Theyre a 7805 replacement that runs cool. 

 

https://au.element14.com/murata-power-solutions/oki-78sr-5-1-5-w36-c/dc-dc-converter-switching-reg/dp/1814499?st=OKI-78SR-5/1.5-W36-C CONVERTER, DC/DC, 1 EA O/P, 7.5W, 1.5A, 5V
 

ill be using these on my 2600’s and zx spectrum

[+Stephen Moss]

I am not sure how/where you are thinking of fitting it but you cannot simply just connect it in to the same place on the PCB as Q12 as...

a) The 5V parts of the Lynx circuit the relative to the 9V power rail not the battery/power pack ground, so the "single point ground" as it is called on the schematic is actually floating at 4V (9-5) relative to true ground.

b) The only 9V source on the PCB pads of Q12 is its gate voltage which is a switching signal itself and so not a good source for regulator, plus you cannot draw enough current from the outputs of the output pins of the 4069 that provide that signal to power the rest of the circuitry anyway.

 

There are ways of fitting an alternate regulator circuit and I recall seeing posts on the subject before, unless someone posts some links to previous posts on the matter in reply I suggest you use the forums search mechanism to try finding them, although I do not guarantee that any instructions you find are necessarily the correct way of doing it.

 

Also, if you are not already aware of it DC-DC converters conventionally use high frequency switching which can create a lot of electrical noise, unless the output is very well filtered there is the potential that such noise may produce noticeable and unwanted affects in the audio and video outputs.

[+-^CrossBow^-]

To add to what @Stephen Moss has already stated. I actually due use DC-DC switchers in some of my classic consoles. In most cases there aren't any issues I've found, however it will cause additional interference on the RF output that wasn't there to begin with. AV upgraded consoles, I've not had issues with doing this. My Sega Genesis model 1 va3 was NOT happy using DC-DC switchers in it. It would cause random graphical glitches in some games and there was noticed logic noise from the audio that wasn't present before on many games. Putting stock linear VRs back into the Genesis resolved those issues.

 

In the case of the Lynx, yes this has been done before and it did seem to work. However, with at least the Agacart flash cartridge that was offered by @rj1307 for a while, it was found that most lynx systems with a DC-DC switcher in them, wouldn't work properly with that flash cart and only by restoring the Lynx back to factory power regulation did it function properly. The thread that goes into the detail on using a Recom brand DC-DC switcher also states at the end, that it is best to just replace out the original components on the power stage as the Lynx original design is very efficient and overall best for power regulation.

[nightmonkeyii]

Thanks guys, this was the info i needed. Seems that the two screen mods dont like it much either. Ill install an original and install a heatsink, and 3d print a bracket for the heatsink. Cheers fellas