Sega CD model 1 power problem.

Fuse was broken after I got it, for reasons unknown. Replaced the fuse and still wouldn't power on. (I suspect due to NES power brick usage, but I can't be sure)
After checking from the trace from the in on the power regulator I suspected the Transistor on TR4 to be broken.
I replaced the transistor on TR4 with an BD652 transistor.

When the megadrive is connected and powered on it gives: Emitter ~3 Volt, Collector ~2.5V and the Base ~1.8V and the fuse ~3V. (which of course to low)
After some measuring the fuse broke, due to my own fault, but then checked those places again and giving similar readings (except for the fuse of course).
Without the megadrive connected it gives no voltage without fuse and with fuse ~13V on both the Emitter and Base and non on the Collector. (Do both the Collector and Base need to get power from the DC jack? Doesn't the Base need to get voltage from the megadrive?)
I also checked if the megadrive it self gave the 9V, which it does.

I can boot some BIOS's trough the everdrive most give, what seems like, a mute static screen. Except for one "Sega-CD Model 2 BIOS V2.00W Emulated Hoax (hack).bin" which also does audio and by pressing A goes from checking disc to please wait. Which it doesn't if it's disconnected.
Apart from that the CDX pro rom says the mega cd doesn't get power. And CDX pro BIOS doesn't boot.
So it at the very least recognizes that a mega CD is attached.

But what can I look at for fixing it?

Edit:
I've replaced the powerboard, which powers the system. But the megadrive still doesn't recognizes the CD-addon. When I power up the megadrive the ready and/or access lights power up, but apart from that it doesn't do anything. So what can it is next to look at?

 

Isn't there a voltage regulator on there somewhere?

 

1.61V in and 1.95V out without R42 and C27 connected (does that even make sense?) 13V in and 5V out with R42 and C27 connected. I've found that their is a high resistance between those 2 (but should be there if I must believe the schematics) but with it it doesn't boot any BIOS or shows a region incompatibility screen, so basically more dead than normal without. edit: I've also noticed when on the static screen and I unhook the sega CD from the megadrive the music starts.

 

something else fried further down the line possibly, have you replaced C27 and R42(eg with new components)

 

I haven't replaced C27 (a capacitor) and R42 I don't even know how to replace as it seems to be a small resistor, about 4 times the thickness of a nail. Is there a way to check if the capacitor is still good without a capacitor checker on the multimeter?

 

Short answer: no. Long answer: no not really.

 

replace tr1

 

with what?

 

a pink marshmallow and some sprinkles

sorry lol couldn’t resist

TR1 is a transistor like TR4, check it to see what it is(im not sure and cant be annoyed opening my mega cd) if you're not sure it should have some writing on it or if it's blown to bits then im sure someone will know.

the only thing you will be able to check on them caps / resistor with the multi meter is if theres continuity if your meter doesn't do capacitance(and resistance of resistor).

if there's no continuity replace both, also test any other transistors in the area if the wrong power supply was used there's probably a few things that went pop/died

hope that makes some sense i've not had any sleep

you could always try looking for a sega cd with a dead laser and just swap out the power supply board

 

I knew TR1 is a transistor but it's a different one from TR4 and far smaller and I can't find writing on it (but it looks fine).

Well there is continuity on C27... and on R42. Just not the connection between them (or anything on the same line with R42)

I'm already looking, and I think I found one with the same part number, so that might fix it.

with what?

 

Only TR3 and TR4 are related to power. TR1 and TR2 are related to the audio output. >_<

TR3 is a 2SC1623 and TR4 is a 2SB943.

 

Before I jump the gun. What voltage needs every prong have?

 

If you really want to test if the power circuit is the reason why it's failing, just remove TR4 and jumper it's collector and emitter pads on the circuit board.

That will make the MEGA-CD be able to power on (if the fault is related with that circuitry).

The side effect is that the MEGA-CD will not power off when the Mega Drive unit is powered off. But for testing that should be fine.

About voltages, you're supposed to have 5V on the third pin of the IC which is on the black heatsink. It's a UPC2405, which seems to be a (Made by NEC) high power version of the well known MC7805 from Motorola...

 

I've tried jumping TR4, no luck... (with and without C27 and R42) not even the LED's blink...

 

got any pictures of the damage??

I have a spare pcb that power up and works but sound is not working.

 

There doesn't seem to be any visible damage to it... Otherwise I guess the problem was easy.

edit:
PM'ed

 

Just a quick question. Is any model 1 power board compatible with any sega CD model 1 (as in pal or later model 1 powerboard in an early asian model 1 sega CD)?

 

The power boards are different, but you can swap them no problem as electrically they're compatible.

The ones made for ASIA/Japan have slightly lax design regarding EMI emissions so it can cause some interference on old ass TV sets. Besides that, they should operate pretty much the same.

@Bart_Simpsons: As per "no sound" it's a problem caused by bad capacitors on the power board. Have them replaced and it will work again.

 

I've just received Bart_Simpsons Sega CD power board, which powers the system. But the megadrive still doesn't recognizes the CD-addon. When I power up the megadrive the ready and/or access lights power up, but apart from that it doesn't do anything. So what could be the problem now...?

 

Can you please take HIGH RESOLUTION pictures of the MEGA-CD main board ?