Power for Supergun

[Hojo_Norem]

My supergun project has hit a stumbling block.  Im working on the power supply section and I have built my 5v regulator based on a LM338 (a 5 amp adjustable regulator) using a diagram in the datasheet.

I got it built no problem and with the 12v supply from my mini switchmode psu and a led attached I can adjust the regulator so its pretty much bang on 5 volts.

I tap off the 5v to feed the RGB switching voltage on my SCART connector and I tap the 12v to feed the 12v input on the JAMMA connector.

Now when I connect my arcade board and connect the power to the psu (Golfing Greats atm, not risking my MVS yet...) the output voltage on the regulator plummets to about 0.6 volts and wont adjust any higher.  The 12v supply is still running ok.

When I built the regulator circuit I put a 2200uF cap on the input of the regulator and a 220uF on the output.  I'm no expert in electronics so I can't help but think I must have done something wrong somewhere as the game worked fine the last time I used it which wasn't too long ago.

I hope somebody here has an idea as to whats wrong because I have been trying to google the information for nearly 2 hours.

Ultimately tho, I might skip building the regulator and buy a 5v mini switchmode psu and just run the two together, I have plenty of room inside the case to do so.

[ken_cinder]

I can't find any technical info on your board, but have you considered it's a board that requires -5v?
Also have you tried not putting a cap in after the regulator? Your regulator is outputting 5v, what's the need for the cap? That's kinda like taking a 5v AC adapter for a piece of equipment that requires 5v and putting a rechargeable battery on the line you plug in. Doesn't really make sense to me. (Mind you my knowledge isn't great either, I'm still learning from everyone here)

[Hojo_Norem]

I can't find any technical info on your board, but have you considered it's a board that requires -5v?
Also have you tried not putting a cap in after the regulator? Your regulator is outputting 5v, what's the need for the cap? That's kinda like taking a 5v AC adapter for a piece of equipment that requires 5v and putting a rechargeable battery on the line you plug in. Doesn't really make sense to me. (Mind you my knowledge isn't great either, I'm still learning from everyone here)

I know the board doesnt need -5 volts as I have had it working from a Amiga psu in the past with no problems.  As for the cap, its there because its there on the datasheet diagram.  I don't really understand what its for.

[NeWmAn]

Did the board really worked before with that power supply?

I can't find any technical info on your board, but have you considered it's a board that requires -5v?

I'm not 100% sure, but -5V is used for the audio amp. Without it the game should still boot and display normally.

 

[viletim]

butter_pat_head,

Linear IC regulators are pretty simple devices...not much to go wrong. It's not a good idea to regulate a 12v line down to 5v with one of thses things. You'll be wasting a fantastic ammount of power with efficiency of only 40%.

Use another switchmode PSU for the +5v rail, or maybe you could use an old PC power supply and have both 12 and 5 volt rails.

BTW, -5v was required for the really early EEPROMs which also needed +5v and +12v too. I don't think any arcade boards from the early 80s onwards need this rail.

[NeWmAn]

BTW, -5v was required for the really early EEPROMs which also needed +5v and +12v too. I don't think any arcade boards from the early 80s onwards need this rail.

A -5v line is part of the Jamma standard pinout (1986?) so there could be some not-so-ancient board that uses it (only for the audio amp).

Anyway this is obviously not the problem here:

the output voltage on the regulator plummets to about 0.6 volts

Are you sure that the game board was working with YOUR power supply before?

[Hojo_Norem]

Anyway this is obviously not the problem here:

the output voltage on the regulator plummets to about 0.6 volts

Are you sure that the game board was working with YOUR power supply before?

It wasn't that long ago since I had last had that board running without problem on an Amiga psu (+5v ~3A, +12v ~500ma).  When I get back from work Im going to double check the board with that psu to make sure that no damage has occured since the last time it was working.  

[NeWmAn]

Sorry, what I wanted to know was if you were sure your game board was working with your LM338 self-built regulator.

Can you post the circuit you used for the regulator?

BTW. I would do what Viletim's suggested, a cheap PC power supply will be perfect for a  supergun

[Hojo_Norem]

Sorry, what I wanted to know was if you were sure your game board was working with your LM338 self-built regulator.

Can you post the circuit you used for the regulator?

BTW. I would do what Viletim's suggested, a cheap PC power supply will be perfect for a  supergun

I'm using the '1.2v to 25v adjustable regulator' circuit on page 6 of this datasheet for the LM338.  The only changes I have made are a added 2200uF cap on the input (I looked at various schematics for 'high current' regulator circuits and most of them had a similar cap.  The 2200uF is the largest value I had to hand at the time) and a load resistor and LED on the output

As for Viletim's suggestion, that has always been my backup plan of sorts.  If I can't get this regulator to work all I need to do is buy the 5v model of the switchmode psu I'm using for the 12v supply.  The psu is small enough that I can fit two of them unmodified inside my case.  I suppose it does add a bit more to the cost my my supergun, but I do get the added bonus of some extra current.  But I would still like to try to get the regulator working first.

[ken_cinder]

Wait a minute, am I to understand that your board requires +5v AND 12v, and you're powering it off a single 12v supply? Doesn't that leave you lacking the necessary voltage required?

[kendrick]

Considering the comparative cost, why not a good old 7805 for voltage regulation? The point of an adjustable voltage regulator is if you need it for testing on a bench, or some other temporary application. That it's adjustable is probably why there's such a drop in voltage under a real load.

-KKC

[NeWmAn]

I'm using the '1.2v to 25v adjustable regulator' circuit on page 6 of this datasheet for the LM338.  The only changes I have made are a added 2200uF cap on the input (I looked at various schematics for 'high current' regulator circuits and most of them had a similar cap.  The 2200uF is the largest value I had to hand at the time) and a load resistor and LED on the output

As for Viletim's suggestion, that has always been my backup plan of sorts.  If I can't get this regulator to work all I need to do is buy the 5v model of the switchmode psu I'm using for the 12v supply.  The psu is small enough that I can fit two of them unmodified inside my case.  I suppose it does add a bit more to the cost my my supergun, but I do get the added bonus of some extra current.  But I would still like to try to get the regulator working first.

Is the circuit the one on page 7 or one of the 2 of page 6? :huh:
Anyway there are values provided for the resistors, have you used those? And the bigger capacitor is on the output side, not on the input...
I'm rather curious about what is the max Amperage that the 12v switching power-supply can provide, and what happens if you try to power something else than the game pcb with your regulator.

The point of an adjustable voltage regulator is if you need it for testing on a bench, or some other temporary application.

AFAIK. Arcade PS need to have an adjustable +5v line to compensate for the different boards requirements, so it's not an useless feature.

[Hojo_Norem]

Considering the comparative cost, why not a good old 7805 for voltage regulation? The point of an adjustable voltage regulator is if you need it for testing on a bench, or some other temporary application. That it's adjustable is probably why there's such a drop in voltage under a real load.

-KKC

AFAIK a 7805 can only handle 1A reliably with cooling, any more and power transistors are needed or multiple 7805s in parallel.  After googleing around for a while I figured that using a adjustable regulator capable of handling higher current would be suitable.

Anyway, Ive gotten round to testing my game pcb with a known working psu and it works with no problem so I think I can safely say it isn't a fault with the pcb.

[Hojo_Norem]

I'm using the '1.2v to 25v adjustable regulator' circuit on page 6 of this datasheet for the LM338.  The only changes I have made are a added 2200uF cap on the input (I looked at various schematics for 'high current' regulator circuits and most of them had a similar cap.  The 2200uF is the largest value I had to hand at the time) and a load resistor and LED on the output

As for Viletim's suggestion, that has always been my backup plan of sorts.  If I can't get this regulator to work all I need to do is buy the 5v model of the switchmode psu I'm using for the 12v supply.  The psu is small enough that I can fit two of them unmodified inside my case.  I suppose it does add a bit more to the cost my my supergun, but I do get the added bonus of some extra current.  But I would still like to try to get the regulator working first.

Is the circuit the one on page 7 or one of the 2 of page 6? :huh:
Anyway there are values provided for the resistors, have you used those? And the bigger capacitor is on the output side, not on the input...
I'm rather curious about what is the max Amperage that the 12v switching power-supply can provide, and what happens if you try to power something else than the game pcb with your regulator.

The point of an adjustable voltage regulator is if you need it for testing on a bench, or some other temporary application.

AFAIK. Arcade PS need to have an adjustable +5v line to compensate for the different boards requirements, so it's not an useless feature.

Sorry my fault, the page which the schematic in question is on is labeled page 6 but its on page 7 of the PDF file.  Its the bottom schematic of the 4 on the page.  I used the resistor values on the schematic.  As for the 12v psu it is rated at 3.8A.

I can't really test the regulator on anything else because I don't have anything else which needs a significant amount of current at 5v.

[viletim]

butter_pat_head,
Perhaps your regulator is faulty? Try connecting a the adj pin to ground. You should measure 1.25v between output and ground and maybe load it with a lightbulb or something. If not, your regulator is faulty.

But it's still a really bad idea, especially if you're going for a small size. Where are you going to put the massive heatsink that I assume you've mounted this regulator on. And you are using the TO-3 version? The TO-220 package won't dissipate nearly enough power. Basicaly, you're going about this the wrong way. An arcade PCB needs +5V @ Heaps of amps and +12V at very little (mainly for audio amps, wihch you may not even use on a supergun). So to use a gigantic power supply (your +12v supply is way to wimpy anyway) and simply waste 60% of it's output is just going to make your supergun big, heavy and very warm!

Surely you can just pick a PSU out PC that someone has abandoned at the side of the road and use that, can't you?

[Hojo_Norem]

Ive seen how small some people around here have made their superguns with integral powersupplies and one of them was smaller than the case I'm using for mine.  If I want to do something similar then a PC powersupply is out of the question.  This regulator business is getting me nowhere.  It could be a faulty regulator but at this stage after messing around with it so much I guess my best course of action would be plan B: replace the regulator circuit with a separate 5v switchmode psu.  The one I'd be using is rated for 5 amps.

Anyway guys, sorry for troubling you with this, I should have realised that it wouldn't work in the first place.

Surely you can just pick a PSU out PC that someone has abandoned at the side of the road and use that, can't you?

Unfortunately people around where I live don't chuck things out at the side of the road anymore... well nothing decent (like pc parts) anyway. ^_^

[Drakon]

do what I'm doing, use the retard board!!!!

http://cgi.ebay.com/Arcade-supergun-motherboard-for-jamma-classics-Mk-I_W0QQitemZ250332607167QQcmdZViewItemQQptZUK_Video_Games_Coin_Operated_MJ?hash=item250332607167&_trksid=p3286.m63.l1177

yes you need a PC power supply and that makes it substantially bigger.  But it's not much more money than buying a jamma harness...and talk about easy to hook up