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Old 01-23-2023, 06:03 PM   #1
sfernandes
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Default Sega Dreamcast NTSC-U Revision 0 Launch Unit GD ROM PCB Board Short

Hi everyone,

Symptom: When I press the power button the power LED lights up for a second and the fan etc spins for a second then the unit turns itself off and will not do the same thing again unless I unplug the power cable for a few minutes then plug it back in otherwise if I just turn the power switch off and back on right after it comes on for a second it will not come on again unless like I said unplug the power cord for a few minutes then plug it back in.

What I have done to try to isolate the issue so far:

The system powers on and stays on with the GD ROM assembly disconnected. I then decided to take the GD ROM PCB board out of the assembly and connected just the GD ROM PCB board to the system and I get the same fault condition explained on the first paragraph. Because of this I think the fault is with the GD ROM PCB board and not the motor/ laser assembly.

I decided to poke around the SMD caps with my in circuit ESR meter tester and cap C20 read shorted.

I decided to remove C20 from circuit and it tested fine and within ESR spec.

I then decided to do a continuity check using my DMM on the pads of C20 from the + to the - and to my surprise it beeps continuosly, so C20's + and - pads are shorted to each other. I believe that's a problem because I have never seen a circuit that has that kind of setup intentionally.

I then decided to follow the traces in each direction and I found that also C21 also reads shorted. I removed it from circuit and it reads ok. I checked continuity on it's pads and same as above both the + and - pads are shorted to each other. There are no solder bridges or anything like that just in case anyone is wondering.

So to me I think this GD ROM PCB board has a shorted component somewhere that's causing this I just can't seem to track down what is shorted.

I decided to check the Resistors at R212, R213 and R211 the readings are...

- R212 = 21.25K according to the schematic for this GD ROM PCB board I should be getting 39K, but not sure if 21.25K is still within tollarance or not.

- R213 = 08.96K according to the schematic for this GD ROM PCB board I should be getting 10K, but not sure if 08.96K is still within tollarance or not.

- R211 = 14.69K according to the schematic for this GD ROM PCB board I should be getting 15K, but not sure if 14.69K is still within tollarance or not.

Not even sure if bad resistors could cause the phenomenon I'm experiencing of having the + and - capacitor pads shorted together even with the cap removed.

Although I'm not too good with reading schematics and understanding them I do have the schematic of this GD ROM PCB board and have attached it below.

I have also attached pictures of both sides of the GD ROM PCB board below. Please keep in mind that in the pictures you will see some caps removed. I have removed them for troubleshooting purposes so I could see where the traces are running underneath. You will also see some sharpie marks that mean nothing it was just to help me on my troubleshooting steps.

I would appreciate if someone could help me find the short and tell me where I should be looking.

Thanks in advance.
Attached Images
File Type: jpg PXL_20230123_235958146~2.jpg (929.8 KB, 9 views)
File Type: jpg PXL_20230124_000048443.MP~2.jpg (908.8 KB, 6 views)
Attached Files
File Type: pdf Dreamcast GD-ROM XU937 (1).pdf (392.1 KB, 4 views)
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Old 01-23-2023, 08:13 PM   #2
stj
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Default Re: Sega Dreamcast NTSC-U Revision 0 Launch Unit GD ROM PCB Board Short

c62, c63, c64
u2 - << wouldnt surprise me, those drivers fail on ps2's a lot
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Old 01-23-2023, 10:38 PM   #3
sfernandes
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Default Re: Sega Dreamcast NTSC-U Revision 0 Launch Unit GD ROM PCB Board Short

Quote:
Originally Posted by stj View Post
c62, c63, c64
u2 - << wouldnt surprise me, those drivers fail on ps2's a lot
c62, c63, c64 all check out ok.

U2 is a BA5986FM it very well could be the problem as it's on the same circuit the shorts are on. How would one test it with a DMM to find out if it's bad or not?

If I remove it from circuit and if the shorts on the cap pads appear normal would that tell me it's the fault? Or would that test not be accurate because it's missing from the circuit?

Where do you purchase your BA5986FM from when you fix PS2's? Where is the best place to buy it?

Thanks in advance.
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Old 01-24-2023, 08:19 AM   #4
stj
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Default Re: Sega Dreamcast NTSC-U Revision 0 Launch Unit GD ROM PCB Board Short

you lift the chip or atleast lift the leg that connects the 12v
if the short is gone from the board but the chip pin is short to ground then it's bad

i usually find such chips by looking through my stash of old pc cd/dvd drive pcb's i keep for parts.
you can look at aliexpress though.
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Old 01-24-2023, 08:10 PM   #5
sfernandes
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Default Re: Sega Dreamcast NTSC-U Revision 0 Launch Unit GD ROM PCB Board Short

Quote:
Originally Posted by stj View Post
you lift the chip or atleast lift the leg that connects the 12v
if the short is gone from the board but the chip pin is short to ground then it's bad

i usually find such chips by looking through my stash of old pc cd/dvd drive pcb's i keep for parts.
you can look at aliexpress though.
Thanks I'll try that and report back.
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Old 01-30-2023, 10:49 PM   #6
sfernandes
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Default Re: Sega Dreamcast NTSC-U Revision 0 Launch Unit GD ROM PCB Board Short

Quote:
Originally Posted by stj View Post
you lift the chip or atleast lift the leg that connects the 12v
if the short is gone from the board but the chip pin is short to ground then it's bad

i usually find such chips by looking through my stash of old pc cd/dvd drive pcb's i keep for parts.
you can look at aliexpress though.
Ok so I finally had some time to pull the chip and sure enough out of circuit the chips 12v pin is shorted to the chips ground pin so it's for sure the culprit. The cap pads no longer read as shorted with the chip out of circuit as well.

Now to find a replacement. Thanks for your help I appreciate it.
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