Old Turbo Duo Repair Not Going Right

[DirtMonkey]

I have an old Turbo Duo that I am repairing.  I got it from someone who had it as a childhood system and it hasn't worked in like 20 years.  It was sent off to Radio Shack way back in the day and they sent it back non-repairable so now I am attempting it.

First off, a few caps were blown so I started with a few cap replacement.  A few pads were damaged but I ran jumper wires to the proper places and all is good.  I tried the original power supply and found out after a bit of testing that it was completely dead.

I then modified a Genesis 2 power supply to work with the DUO and made sure that the polarity was reversed when I did up the cable.  I plugged in a TG16 game, hooked it to the TV and turned it on.  First thing I noticed is that the CD motor was spinning and the laser was in a bit of a focus spasm.  I disconnected the laser assembly and turned it back on.  Next, Kid Courage came on the screen in perfect picture and I played it for a few minutes to make sure that the system accepted input.  Cool, best progress in over 20 years!

20 Mins later the Genesis 2 power supply died on me.  Very interesting since it is rated at 9V and 1Amp which is more then enough to power this system and there is no reason it should blow so I chocked it up to a bad power supply.  I then switched to my desktop  power supply and provided it the 10V 1A power requirements and got no kid courage on-screen at all, just a white screen. 

Next, I made up another Genesis 2 power supply.  I have an abudance of them and it worked the first time.  This time I interrupted the power line with my multi-meter and checked for ampage drain thinking that perhaps it was trying to draw to much power.   Yep, over 3 AMPS were being drained by the system!  3 AMPS! 

So, something in the system is trying to REALLY drain power and I am not sure what to look at now.  I did notice that the voltage regulator on the right side was running very hot but would a faulty voltage regulator draw more power or perhaps it was running hot because of the power drain?  I am not an electronics engineer but I do know enough to be dangerous. 

Where would you start from here to diagnose and fix this system?  I *REALLY* want to get it working and feel like I am close!

[wilykat]

Someone's shorting out.  If the system played a game for a bit, the regulator itself is probably not the cause. Otherwise you wouldn't be able to play anything.

Did you check to see if anything else felt hot?  A motor drive IC maybe?  Also it is possible you messed up the cap repair and created a bridge or something.

[DirtMonkey]

I will get a chance to mess around a bit more with it on Monday.  For shits and giggles, I am going to wire up another Genesis 2 power supply and flick it on to see if I can get it to come back to life again to check for warm components.  I have done a lot of recaps before but not on a DUO so I am pretty confident on my workmanship there but there is always a first.  Today I even did a full express recap which went really well and fired up right away.  2 pads were damaged beyond repair with acid on that guy. 

[mickcris]

you should not reverse the polarity of a genesis 2 power supply. both the Duo and Genesis 2 have a center positive tip.

[DirtMonkey]

Well, that is an interesting situation.  I must have read the power supply picture incorrectly on one of them.  I will post back tomorrow with an outcome.

[mickcris]

the genesis 1 is center negative so maybe that is the power supply you have and not a genesis 2?

[thesteve]

ok the 3A is a short somewhere
the spinning motors could be the cause
check for a bad via by the 47uf caps near the LED
check ohms from 5V to ground
check ohms input power to ground

[NightWolve]

The Turbo Duo's fuse is 3 Amps, should've burned out by the sound of it.

In any case, good luck find the short.

[Brraap]

You need to replace ALL the caps..if you haven't done so....and the board needs to be cleaned...I had to repair one with similar symptoms one time and just like the thesteve said...it was a bad via...washing the board clears up all the crap and cleans out the via's. It is then much easier to repair

[DirtMonkey]

As mentioned ALL caps had been replaced on this board prior to me posting here.  AND, the problem has been FIXED!  Thanks for the help guys.  The issue was exactly what I thought it was to start with and I should have gone with my gut feeling.  The Turbo Duo has two 7805 regulators.  It appears one of the regulators is for the CD portion of the system and the other one is for the card based portion of the board. 

The 7805 for the card portion of the card had the proper input of power and would output a steady 5V output BUT the 7805 on the CD portion was pulling a TON more power trying to output to 5V but only really putting out about 1.8v while drawing a ton of amps.  This was causing the heat sync to get really hot on top of that. Because of this increased amp draw, it was causing the power supplies to short out and die in the case of the original power supply and the Genesis 2.  The aftermarket Genesis 2 that I used lastly just didn't have the juice to output the amps the system was drawing while maintaining the voltage to get the board portion of the system to display anything other then a white screen. 

In the end, it took me hooking up my old desktop power supply unit to the board and providing it the power it needed to actually get good readings on the regulators.  And yep, confirmed, bad 7805.
This 1.8v low output was what was causing the cd drive to spin slightly and become somewhat responsive but not totally responsive as it should with 5v.

[NightWolve]

So just swapped in a traditional 7805 ? Somewhere around here we talked about newer regulators that work better/last longer (safer breakdown scenarios). Anyways, congrats!

[DirtMonkey]

Nope.. Swapped in a new 7805 from Digikey.  I get all my electronics from them.
https://www.digikey.ca/product-search/en?keywords=NCP7805TGOS-ND