Dreamcast powers on, no audio/video/fan?

Discussion in 'Repair, Restoration, Conservation and Preservation' started by MangledLeg, Apr 9, 2019.

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  1. MangledLeg

    MangledLeg Peppy Member

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    Hi all,

    Have an odd issue with a Dreamcast - I switch it on and the power LED lights up and the GD-ROM seeks for a disc, but no audio or video is on screen and the fan doesn't spin up.

    I've checked for obstructions around the fan (all seems working and it spins freely if I use my hand) and it's plugged into the controller board nice and securely. As I said above, the LED switches on as well.

    I've checked the power supply and all the output voltages are solid.

    I've swapped out the BIOS so my first step is checking to make sure everything's in order there, but does anyone have any other ideas on what's happened with this one I should look into? Is this related to an issue with the fuse on the controller board? The other mods I've done are changing out the battery with a vertical battery holder with new rechargable battery installed, cap and resistor swap on the PSU (Japan/100v to Australian/220-240v), R422 bridged for PAL colour encoding and R512 on a switch to program the flash memory (currently set to read-only).

    I'm very confused with this one, hopefully it might just be something with one of the pads on the BIOS but figured there might be some other suggestions I can look into. Thanks in advance!
     
  2. TriMesh

    TriMesh Site Supporter 2013-2017

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    Which model is this? If it'a a VA1 (I.E. 3 pin fan connector), then it won't boot if the fan isn't running. The fuse just powers the controller ports, and won't affect the fan operation.

    The first things I would check are the fan, the soldering of the fan connector to the controller PCB and the flex cable connecting the controller board to the main board. I assume you don't have a spare unit there to swap parts with? That's by far the easiest way of tracking down these sorts of problems.
     
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  3. MangledLeg

    MangledLeg Peppy Member

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    Thanks TriMesh - it's a VA0 Japanese model so I'm unsure what idiosynracies are there, but I've got working spares around to test. I reckon there's one or two cold joints on the BIOS I'm going to reflow now, then I'll take a look at the controller board and PCB to make sure everything's in order, including checking what voltage is hitting the fan connector.

    Any other ideas for VA0 revisions I should keep an eye on?

    Edit: Just reflowed a few connections and plugged everything back in. The fan on the controller board is now working, GD-ROM continues to work, but nothing appears on screen and when plugging in a controller the VMU stays blank. Used the same cables and controller with a working DC and all's good. Tried the problematic DC on RGB in case there was an issue with the video encoder's composite/s-video output, but all's good.

    I have another spare VA0 region free BIOS around so I'm considering removing the current BIOS in case I've done something daft while trying to install it, whacking in this one and trying again. I've also got the original BIOS too that can be added back in if necessary.

    In the vein as my initial post - any other ideas I should keep in mind for this one?
     
    Last edited: Apr 10, 2019
  4. TriMesh

    TriMesh Site Supporter 2013-2017

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    Yeah, at this case I think the most likely cause is with the chip install. The problem with a bad fan disabling the console doesn't apply to the VA0 anyway - that just has a 2 pin fan and the console doesn't have any way of detecting if it's running.
     
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  5. MangledLeg

    MangledLeg Peppy Member

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    Thanks mate - I’ll re-do the BIOS tonight and see how we go. I was doing a bit more testing before I finished up last night andit turns out a video signal was going through to the TV, but since I had blue-black set on my CRT it was giving me the generic screensaver instead of displaying a black signal. This adds weight to your theory it’s BIOS related.

    Will post how I go!
     
  6. MangledLeg

    MangledLeg Peppy Member

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    I think my DC is possessed by a demon of some sort!

    I swapped out the BIOS last night for another one running the region free bios with the dev splash screen. The DC switches on normally with a black screen for around 5 seconds, then the screen goes straight to the DC logo (as in, what it sits at after the boot splash has finished) with no audio. It’ll sit at the DC logo for around 5 minutes, then it’ll go to the usual options screen with play/VMU management/etc. I select to start a game and it reports there’s no disc in the GD-ROM drive. The GD-ROM when you put in a disc and close the lid sounds like it’s doing the usual spin up/read/spin to normal speed process my other DCs do, but won’t load anything.

    I’m thinking the console might be toasted - I bought as junk from a Japanese auction a few years back and made the mistake of not testing before I pulled it apart to mod. As a final check I’ll tweak the GD laser and make a note of the values with the multimeter to see if that helps reading and loading games and double-check all the soldering on the BIOS I’ve just whacked in there in case I’ve missed something. If none of this does anything I’ll hold onto it for parts I guess!
     
  7. MangledLeg

    MangledLeg Peppy Member

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    .... and in good news - all is well!

    In case anyone finds themselves in the same spot I did the following: I resoldered all the pins and checked continuity again once complete, all was good. I then cut fresh cables for the bridge between pins 23 and 44, as well as the one from pin 1 to the tiny spot that leads to pin 7 of the nearby IC. Once I did this the DC was booting up faster, the BIOS revision was showing in the menu screen but was still a little buggy. Cue the lightbulb moment and I whacked in the modem - this finished everything up and it's running perfectly.

    While leaving the modem off was clearly a daft move (I didn't realise the DC would get so angry without something in that port), I'm going to console myself with the thought that the extra work on the BIOS also helped sort this out :p
     
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  8. Ergot_Cholera

    Ergot_Cholera Flaccid Member

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    All the Dreamcasts I've ever owned worked without the modem attached.
     
  9. Bad_Ad84

    Bad_Ad84 The Tick

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    Same.

    Your issue seem related to a damaged/shorted trace or an iffy gdrom connector.

    If you don't have the clock from the gdrom getting to the dc, it acts like you describe with it being slow etc.
     
  10. darcagn

    darcagn Site Supporter 2013, Site Supporter 2014

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    There's till something wrong, because you definitely don't need the modem attached. Some consoles didn't even have a modem, and just used a dummy piece of plastic on the back.
     
  11. -=FamilyGuy=-

    -=FamilyGuy=- Site Supporter 2049

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    Some came with a dummy modem that looked like a termination though. But I think they'd work without it nonetheless.

    There's something fishy here.
     
  12. darcagn

    darcagn Site Supporter 2013, Site Supporter 2014

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    Yeah there exists both one that terminated the G2 bus and another one that’s just a piece of plastic. I have the plastic one in my collection but not the terminated one, I think it’s more rare. Not sure.
     
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