A quick lesson in Data East power supplies

[andtan]

Is someone able to give me a run down on the +5 volt DC power generation circuit for a Data East (Jurassic Park) power supply board: p/n 520-5047-02?

JP was refusing to boot and all I was getting was some GI lights and rubbish on the DMD - all the LEDs on the CPU board were off. A quick inspection showed that there was not +5 volt at Power supply Test Point 1, instead only about 0.85 volts, and the -12 volt was also a bit off.

I checked the fuses, and caps and replaced the Bridge rectifier (DB1) as it was a bit suspect, and a retest showed the 12 volts were now ok, but still no +5 volts.  Next I unplugged all the power supply board connectors bar CN1 and CN2 and hooked the DMM up, and I then the +5 volts test point had 11.3 volts. This reading stayed constant until I connect either the DMD (CN5) or CPU / Sound (CN6) connector, and then it drops down to 0.85 volts again. If I leave it powered on for a minute or so, TR4 starts to get quite hot.

When I do the same testing on my Tommy power supply (same model power supply board) I get a constant +5 volts at the test point no matter which connectors are connected / disconnected.

When I compare the voltages in the +5 volts circuits between the two boards, I get the same readings coming off the Bridge rectifier (DB1), at C2, at diodes D2 and D3, but once it gets to IC1 (MC1723CP) it should have 5 volts coming out at the pin that goes to the test point, but it has 11.3 volts. The transistor TR5 (2N6057) also has 11.3 volts at the yellow wire (B) instead of 5 volts.

From this I am thinking (hoping) that there is a fault with either IC1 or TR5 that is preventing the output of the 5 volts. As I have neither of these components on hand I will have to order some, but I was hoping someone could enlighten me as to which component (IC1 / TR5) actually looks after generating the 5 volts. I am also open to the possibility that I am way off the mark and have no idea what I'm talking about

[flippnaussie]

Can you get the printing off the components?
We'll need the part numbers to help decode the circuit and the faulty part.

Simon.

[ddstoys]

The capacitors on these power supplies are notorious for leaking acid as the 5v. There are two capacitors to the lower right of the heat sink I'd be removing these.

   If it stinks when you heat up the solder your caps are stuffed

[Mr Pinbologist]

The capacitors on these power supplies are notorious for leaking acid as the 5v. There are two capacitors to the lower right of the heat sink I'd be removing these.

   If it stinks when you heat up the solder your caps are stuffed

+1 to Daniels advice, just replace them  I had the same issue with a Jurassic Park i restored some time ago, ie not booting.. replacing all the caps to do with the 5v regulator circuit fixed it  Just about ALL of the electrolytic caps on the board had that smell when the leads were heated up.

My old boss used to call that smell the 'cat piss' smell 

[Homepin]

My old boss used to call that smell the 'cat piss' smell 

Exactly what we used to call it - it's an unmistakable stench.......

[andtan]

Thanks guys,

Guess I'll 'bust me some caps'

[beaky]

if they have leaked make sure you remove all of the gunk that has leaked out and make sure the copper that has been contaminated is made shiny with some very fine sandpaper.
i then tin these tracks with solder