Mega-CD Slow Disc Tray, 3rd Party PSU

[PureChaosXGaming]

I recently purchased a 3-in-1 PSU for the Model 1 Mega Drive, Mega-CD and 32X, so all 3 can be powered by a single PSU.
https://en.retrogamesupply.com/collections/sega/products/power-supply-all-in-one-for-sega-megadrive-genesis-mega-cd-32x

The PSU is rated at 9v 3a, the original Mega Drive/CD PSU is rated at 10v 1.2a... not sure about the 32X PSU though.

When I first got the PSU, I only went so far as to test everything powered up, which it did. I only recently tried to play a Mega-CD game. I opened the disc tray and noticed it was opening very slowly. I was a little confused as the last time I used it, the tray opened fine. It was also slow at closing, and would struggle to pull the tray in all the way for disc to start spinning.

Out of curiosity, I tried the original PSU in the Mega-CD and the 3-in-1 in the Mega Drive. The disc tray opened and closed fine and the disc was able to spin. Next, I swapped PSUs around. The 3-in-1 in the Mega-CD and the original in the Mega Drive. The disc tray was again slow to open and close.

So this 3-in-1 PSU is definitely the culprit, and seems to be underpowered to run the Mega-CD properly. FYI.. I have contacted the seller, but haven't heard back as of yet.

Does anyone have any ideas about this? Is the rating on the 3-in-1 PSU too low? It's only out by a single volt, and the amps should be enough (apparently) for all 3 devices at the same time (I don't have a 32X yet). Or is there possibly a component on the Mega-CD mainboard causing this effect on the disc tray when used with a third-party PSU?

Any help would be much appreciated, thanks

 

Video of the problem:

 

 

[Austin]

Yeah that's super strange. I mean, if it's a power issue, then it's probably not that strange.

 

I had a similar issue a few months back but it was due to a belt problem. Probably wouldn't hurt to check that, but your video clearly shows a difference between the two power supplies.

 

I've always touted this on other threads, but the caps in these consoles probably aren't helping. Best to get them replaced if you can. Wouldn't hurt to check the belt and re-grease the mechs while you're at it.

[+-^CrossBow^-]

I could very well be wrong about this, but my guess is that the DC motor that drives the door is feeding directly off the input voltage from the PSU. The older supplies are rated for 9-10v output, but in reality they put out much more until there is a load on them. Newer supplies tend to use switching converters in them and those put out the exact rated voltage.

 

So, where I'm getting at is that the OEM is likely providing more like 12v or something to the system and the motor is showing this difference.

 

Only way to know is to use a meter and check the voltage at the motor side when it is switched on vs the voltage using the 3-in-1 supply. 

 

I've got a converted gamecube PSU with the three plugs on it that I use to power my setup but I honestly can't recall running the CD unit off its own in the past to compare or notice. I now use a model 2 CD so I really can't easily compare this now. But again, that is my guess is that the OEM is putting out more voltage than rated (Which is normal btw), and the motor is DC fed directly from it, while the newer one is putting out exactly 9v and a few volts difference will matter on the motor speed. I'm also pretty confident that the replacement is fine and won't cause any issues aside from the slightly slower operating motor. And a worn out belt might also show this effect more as well.

 

 

 

 

[PureChaosXGaming]

OK, so... I managed to buy a new drive belt as well as a replacement capacitor kit. After many hours, lot's of patience and multiple swear words, I finally had all caps replaced on the mainboard, as well as having the belt replaced. 

 

Yeah, same problem. Slow moving disc tray. Even added a bit of white lithium grease to the gears, but didn't really help. Maybe the lack of that extra volt really is causing the tray motor to move slowly. As it appears, everything is working just fine, even the motor that spins the discs works without any problems.

 

So, strange... but as long as it doesn't affect the console, it should be fine. I still have both original PSUs so if it comes down to it, I can just use those instead.

[+-^CrossBow^-]

On 3/29/2023 at 11:35 AM, PureChaosXGaming said:

OK, so... I managed to buy a new drive belt as well as a replacement capacitor kit. After many hours, lot's of patience and multiple swear words, I finally had all caps replaced on the mainboard, as well as having the belt replaced. 

 

Yeah, same problem. Slow moving disc tray. Even added a bit of white lithium grease to the gears, but didn't really help. Maybe the lack of that extra volt really is causing the tray motor to move slowly. As it appears, everything is working just fine, even the motor that spins the discs works without any problems.

 

So, strange... but as long as it doesn't affect the console, it should be fine. I still have both original PSUs so if it comes down to it, I can just use those instead.

When you had all opened up, that would have been a good time to check the input voltage going to the DC motor between the two different PSUs... Even if you just solder some wires to them temporarily to run outside the case when it is all put together so you can attach alligator clips or something to see what is happening.

 

But yeah, I'm guessing there is a difference in the voltage going into the motor between the two different PSUs with the OEM likely juicing it a tiny bit more than the replacement.