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SC-3000 with black screen on boot after refurb.
Posted: Fri Apr 23, 2021 2:24 am
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Hi all,
Have had this machine waiting for a recap for a while. Unfortunately, after doing everything I know how, it still doesn't boot. The cartridge I'm using is Basic Level 3 A - It's the only one included with the machine, and is in very good condition (boxed, cleaned). I'll try to dot-point everything to save reading a wall of text: Model: John Sands SC-3000 Symptoms before: -Obnoxious buzz, no display -No power light -"Fish smell" of capacitors Findings: -Caps burst and coated entire bottom of motherboard PCB, and to a lesser extent daughterboard -Dirty but not filthy inside. Dust and caked on grime around heat outtakes -Cartidge port relatively clean with few signs of cold joints Actions taken -Complete scrubbing of underside of PCB with 99 IPA, and then dabbing off cap juice with towels -Full recap + daughterboard recap -Reflow of all cartridge port connections to motherboard x 4 rows -IPA then "card wrapped in A4 paper" trick to clean out cart port Symptoms now: -Black screen upon turning on. TV is clearly reacting to system -Have tried video out (same as C64 cable) - can't see any reaction on screen from this cable - and RF out, where the screen goes from "snow" to totally blank when power switched on. -Power light is now ON -edit- upon startup there is a slight buzz for a split second, then after about 5 seconds there is a single "beep!". I've left it on for 10 minutes and there is no more sound, and still the black screen. (end result of cleaning & refurb) Is there something else I should be testing? Have a sneaking suspicion the cartridge or cart port is acting up, but no idea where to go from here. Could the RAM be gone like on a spectrum? Where do I check with my multimeter for faults? As a relatively active Game Gear modder/restorer, the limited amount of info on repairing the SC-3000 is frustrating. Thanks for everyone's time. |
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SC-3000 with black screen on boot after refurb.
Posted: Fri Apr 23, 2021 6:28 pm
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Before doing anything else, try cleaning the edge of the Basic III cartridge pcb. Use folded white paper or a pencil eraser. Then test it again.
It's very unlikely that the whole underside of the mainboard was coated in cap juice as you called it. It's more likely a liquid spill. |
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Posted: Fri Apr 23, 2021 8:28 pm |
Thanks - forgot to mention I've already done this. I disassembled the BASIC cart, cleaned up the whole circuit board & replaced the 4.7 uF 25v with a 4.7 35, and scrubbed the edge connector to within an inch of its life. Letting it dry, I went over it with a pencil eraser, then more IPA - it's squeaky clean. |
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Posted: Fri Apr 23, 2021 9:49 pm |
What test equipment do you have available? (Logic tester? Logic analyzer? Oscilloscope?) | |
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Posted: Fri Apr 23, 2021 10:04 pm |
I think the error codes are as follows..
1 beep = check sum error of cartridge rom 2 beep = ram error 3 beep = vram error Id still be looking at the cart edge connector or cart. Possibly theres a bent pin thats not making contact on the connector? Or maybe a dry joint on the cart pcb? |
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Posted: Sun Apr 25, 2021 6:48 am |
Thanks for your reply - unfortunately I'm not this advanced. I have recently upgraded to a relatively in-depth multimeter with capacitance and continuity, which was a huge upgrade on my last volt + ohm MM. Is there anything I can test to see what's going on with this?
Perfect, thank you. I'm a little concerned as this BASIC cart came with a "searched & scanned by customs" tag (Australia) & am worried it has been fried. Too late to raise any complaints now. I'll revisit the cart, and reflow anything I can find on the motherboard's cart connector & the cart PCB. There are two ceramic capacitors on the cart PCB which I didn't replace ( did replace the electrolytic though ) - couldn't read the ratings. Would this be worth looking into? |
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Posted: Sun Apr 25, 2021 10:24 am |
Ceramic caps are generally very reliable.. they should be fine. Have a quick look around the cpu for dry joints and possibly around the mitec chip too. The mitec chip looks socketed so you could lift it out and see what the socket pins look like as well. If it has had something spilled through it they could be a bit nasty.
If you get stuck after that you could take the cart apart and put the board in the socket on the motherboard and check all the data and address line for continuity between the actual eprom and cpu. Look up the pinouts for a z80 and 27c256. D0 on the cpu should go to d0 on the eprom.. the same for d1 through to d7. Then check the address lines... a0 through to a14. |
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Posted: Thu Apr 29, 2021 11:54 am |
Much appreciate your response. Perhaps a clean of the CPU / mitec chip would be a great place to start, however I've ordered a new BASIC cart & will check this first. Feeling as if there might be an issue with it, can't hurt to have a backup. Forgive me as I'm new at this type of troubleshooting. So I should check: against: And run my multimeter on continuity D0 to D7, and A0 through A14? Cheers |
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Posted: Fri Apr 30, 2021 8:29 am |
Is the beep done a single time?
If that, it is normal. Try in an emulator (for instance mess 0.136 works). When basic starts, it makes a single beep. This would suggest that the system is actually booting, but the problem is with the VDP. |
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Posted: Mon May 10, 2021 9:09 am |
Thank you. Yes, it is a single beep. I ordered a new BASIC cart, and the same issue persists. How might I diagnose or repair the VDP? Is it something easily replaceable? |
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Posted: Mon Jun 14, 2021 10:03 am |
Ok! So, some progress on this.
Borrowed an identical SC-3000 that needs a recap. Took the video daughterboard out and: So, looks like the issue is in this. Does anyone know how to test the transistors on the board? Suspecting it's one of those as it has had a full recap. Also, a transistor list might be useful, perhaps can just replace them all? Thanks |
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Posted: Fri Jun 18, 2021 3:58 am |
Probably easier to just replace them all rather than test them. Not sure about what the values should be but there some schematics on that may help:
https://www.smspower.org/forums/13431-SC3000SG1000SchematicsAndTechnicalDetails and https://console5.com/wiki/Sega_SC-3000 |
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Posted: Tue Jun 22, 2021 6:54 am |
Thanks! This was extremely helpful. I found the quoted image with the PAL video daughterboard. Unfortunately it's extremely hard to read the schematics. I took the transistors out of my own DB, and came up with the following: TR102, TR103, TR104, TR107 C945 P137A Best match on ebay: P945 C331 or 2SC945 C945 50V - 150mA NPN General Purpose Transistor TO-92 TR101, TR102, TR105, A733 AQ137 Best match on ebay: 2PA733 A733 50V - 100mA - 500mW PNP GP Switching / Amp Transistor TO-92 TR106 C2001 L237A Best match on ebay: 2SC-2001 TRANSISTOR TO-92L C2001 2SC2001 Can anyone tell me if I'm matching the transistors correctly? It's all practically another language to me. Also, is there an easy modern replacement for the SC-3000 power brick? Thanks again! |
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Posted: Tue Jun 22, 2021 11:47 am |
Not sure about the components but I am fairly sure the power supply is the same as a master system (9v center negative) | |
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Posted: Tue Jun 22, 2021 10:09 pm |
Thanks! I'll pick one of those up. Components ordered. Fingers crossed, appreciate the help. |
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Posted: Fri Aug 13, 2021 10:45 pm |
Replaced all transistors & capacitors. SC-3000 is now working perfectly.
Thanks everyone for the help! |
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