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What the hell Sega..

coops375

Hi all,

 

I recently purchased a Sega Megadrive and a Sega Mega CD2 from ebay.

 

The CD2 was sold as 'untested' which seems to be the chosen word for all electronic devices where the seller doesn't have all the cables to power up and test the unit. The pessimist in me thinks the sellers know the devices don't work and in order to get a little more cash list them as 'untested'.

 

Either way I took the plunge and bought both as they were sold together.

 

Wellll... The CD2 doesn't work but that doesn't matter too much as the Megadrive does image

 

I took both consoles apart to give them a good clean and also to install a 60hz switch on the Megadrive. This is a pretty easy mod helps remove the top/bottom bars whilst also increasing the game speed to what was originally intended.

 

Video showing 50hz/60hz switch -

 

In opening up the consoles I noticed some crazy 'factory' mods. Was this normal practice 30 years ago or something unique to Sega?

 

It looks like the Sega CD2 could be a simple fuse issue which pops when the wrong power supply is plugged in.

 

I've ordered a 9v 1.2a power supply off ebay which is sold as a replacement for the CD2. My next job is going to involve bypassing the fuse with a wire to see if it powers up. (foolish?)

 

Am I correct in thinking that if I take a multi-meter to the motherboard and test some of the resistors, everything should report 0 if the main fuse on the board has blown?

 

Pics from inside both the Megadrive and the CD2 along with the switch I installed. (from research this is a VA6 which has the better Yamaha YM2612 sound chip)

- I've only added the black/yellow/red cables that go to the blue switch, the others were put in place by Sega

 

imageimageimage

  • Never owned one but a wiring job like that suggests this might be an aftermarket modchip, possibly to bypass copy protection. Such mods were especially popular for the Sony Playstation.

     

    - Gough

  • in reply to Gough Lui

    My exact thinking at the time.

     

    However, the Sega CD2 doesn't have any copy protection :0.

  • in reply to coops375

    Looks like you're right. I did some searching for BE2200F01003 and according to this site, it's a bodge fix for a board error they didn't catch.

     

    So I guess I join you in exclaiming "What the hell Sega!?!"

     

    As for the fuse - fuses are relatively cheap, so I'd probably order some spares and only test it with the fuse. Fuses blowing don't guarantee protection of the downstream components - just protection against hazardous events (e.g. fire, explosions) ... so sometimes persistent fuse blowing is a sign that some chip may have gone short because of previous abuse. If the fuse is open, a meter set to measure voltage should measure zero across most parts (excluding the supply terminal to fuse section) with the exception of possible stray voltages. I don't see the fuse myself in your images, so also depends how it's wired as to what it's protecting.

     

    - Gough

  • in reply to Gough Lui

    Thanks.

     

    The fuse is located towards the right and side of the board near the middle. I think it's labeled F301. (first image)

    I'll get a replacement fuse ordered too and replace that and pray that it works.

     

    Problem I have is that there is no indication that the CD2 is working when not plugged into a megadrive. (no LED light or anything)

     

    I've cleaned the pins on the megadrive but that didn't help.

     

    Worst case I'll sell it on ebay as 'untested' (I'm joking)

  • in reply to coops375

    Well, the sure fire test is just to set the meter on continuity or ohms and measure across F301 - if it indicates infinite resistance, you have an open fuse. There shouldn't be any parallel paths bypassing the main power supply fuse, so testing in-circuit shouldn't be a big deal.

     

    If you don't like doing that because it could apply a small voltage/current to the pads, then apply power and measure voltage across F301. It should measure 0V if the fuse is good. If the fuse is bad, it will likely read the full supply voltage or similar (assuming the rest of the unit is a continuous circuit - e.g. power switch is pushed on if it has one).

     

    This also reminds me - D301 looks potentially suspicious as a reverse-polarity crowbar diode. This would serve to "short out" a supply connected that was reverse polarity to "protect" the rest of the board from experiencing reverse polarity, but this often meant high fault currents. If such diodes experienced such an event, they normally would fail shorted, resulting in a dead short if the correct polarity supply is later restored. You could probably remove the diode to test (in circuit is unlikely to give correct results as filter capacitors might well interfere), or check if it gets rather hot when plugged in and switched on. If it does, then it's probably a sign someone used the wrong polarity power supply in the past. If it's truly a reverse-polarity crowbar diode, you could snip it out as long as you didn't apply reverse polarity in the future.

     

    EDIT: Forgot to mention, such crowbar diode failures were particularly common with vehicle radios where people did their own bodge job with wiring ... some people just clipped them out and called it a day.

     

    - Gough