Just another MegaCD1 repair

Hi dudes

After years of wanting one, decided to buy an european MegaCD 1, JVC CD drive, in mint condition and decent price. It boots up, and the reset/try works as expected, the screen animation, sound... everything, but, once the disc is inserted, it spins ok and then megacd´s disc access leds blinks in loops of four times, but no "press start to play" message appears on the screen (it doesnt freeze, the megacd animation keeps running and sounding)

I though on a laser issue, but before trying my luck tinkering with the potentiometers on the laserboard, i tried the complete laser board on a friend´s megacd and it works ok, so i figure the issue its out to the logic board.

As the capacitors were starting to leak (no visible acid but green legs), i changed all of them on the logic board, besides de 100uF. The ones 10uf 6,3v are changed for 10uf 25v (which should work anyways, as they`re the same capacity). Also replaced the ones in the powerboard. Sadly no results.

Seems to be an old board, has has eprom instead of rom. I was thinking that the thing doesnt know when the door actually closed or open, as the the ready led is on and access light flashes, but it asks me to push reset to put a game in, and everything goes as it should but the message "Press the start button" never comes up.

Also tried going to the audio menu before inserting a disc. Actually I can open/close the lid via menu (so i assume the switch on the cdrom part is ok, and that part worked flawless in the megacd of a friend). Once the disc is inserted i can hear it seeking for the first sector or whatever, doing good sound, the same as when used in the working megacd of my friend, but while it keeps spinning the cd, it never showup the tracks, and the access light keeps flashing in 4 flashes loops.

As i had spares here, replaced also the 74HC254, the 74HC86, 74AC74 and the ferranti MB8464A, just in case any of those took care of the open/close/ready part of the logic, but no luck neither.

Also tried reseatting both ribbon cables, but im out of luck.

Maybe that 4 flashes loops indicates some error code¿? The thing seems to be working but some "ok" signal to boot up the cd is missing. Im desperated at this point.

ANY suggestions are welcome

 

did you try an audio cd yet? and are you sure you're using a game that has the right region code?

 

Hi Roberto

Thanks for the reply. Both megacd and megadrive are PAL, as PAL is the original copy or Road Avenger im trying to boot. I also have here some saturn cdr games, which of course wont boot, but using the megacds audio player, should show me how many tracks it has.

Using the megacd's builtin audio CD menú, it doesnt shows up how many tracks are on whatever CD is inserted (it keeps spinning and the láser pickup does the "right" sound, that is it makes the same sound that when I put my cd Drive on my friends megacd) but the machine doesnt hang, in fact, I tried and succeded formatting the sram while the cd that was inserted wasnt recognized at all.

My friend lent me his megacd, and after many tests, all the different parts of my megacd are working ok besides the logic board.

There are many talented guys here, hope someone has a clue on it.

BTW, doesnt exists a rom from sega that makes a check on the megadrive/megacd hardware? I smell that 4 Access LED blinks is an error code actually.

Many thanks again

 

MB8464A (Fujitsu 64KB SRAM for backup). Put the original chip back as it's a low power version.

There's no "diagnosis codes" on the flashing lights. The flashes mean it's trying to read. The front lights are also software controlled, they're toggled by the program running on the MEGA-CD 68000 CPU.

When you try to start a MEGA-CD disc and it freezes on load it's usually a power issue. I'd suggest you finish re-capping the unit. Do replace all the capacitors you did not yet. I re-cap'd my asian MEGA-CD years ago when it was going bad. It behaved almost exactly as yours. It would have a lot of trouble to read discs. The difference is that I never tinkered with any of it's adjusts I went straight to the caps and when I was done replacing them the unit worked as good as when it was new.

 

This whole "lets blindly fuck with the laser to get it to work again without consulting any information on how to actually work with the POTs or learn how to use an oscilloscope" thing needs to stop. Rarely this fixes things and most of the time things end up broken.

 

But according to SOME users on this forum, not all consoles will have their "90's" caps fail....

Back on topic, best thing I did was to replace all the caps in my model 1's Sega/Mega CD's.

 

Hi Ape

English is not my mother tongue, and I do know its far from perfect, but, I dont think I have said I fiddled with any of the pots.

In fact, I wont do it by anymeans, because as i have tried my whole cd board in the megacd of my friend, I can certify the cd board and the láser pickup itself are working flawless.

Btw I finished the recapping on both power and logic board, without success. This is getting on my nerves. Maybe one of the smd resistors or capacitor.in the underside of the board went.wrong....

Im.recapping with fresh.capacitors and.will replace the original sram Module again.lets see what happens

Thanks for the input

 

Recapped the entire unit with fresh caps.

Now it take audio cds, both original and cdr. Instantly, no skipping, no clicking noise, just fine. Sadly it doesnt like any of my games.
As i have said, putting my cd drive unit in another megacd showed up it works.


Any idea?

 

Did my best, but no luck. I suppose there isnt anyone with one spare working megacd1 logic board, right?

 

That can be caused by a bad spindle motor, the tolerances are tighter for data than for audio, I have seen that audio but no game problem on Sega CDX and PlayStation units.

 

Now that you mentioned it, I remember that the height of the spindle hub is a possible reason for such a fault. But the OP mentioned the drive works just fine on other MEGA-CD unit, no ?

 

Yes, my friend has a exactly same (optima 5 one) model of MegaCD and the my cd drive works perfectly on his MCD, and his cd drive also doesnt work on mine.

 

Only things that could cause your problem then are faults around the CD-ROM decoder circuit (the SANYO chip) because what that chip does is convert the i2S audio stream from the CD-PLAYER DSP chip (that drive isn't a dedicated CD-ROM player but actually an "more flexible" CD-Player drive instead) into data and while the SANYO chip is not needed to play audio it's needed for the drive to be capable of properly decode data. On the MEGA-CD I believe it has a pair of 6264 SRAM chips as buffer memory.

 

Resoldered those pair too. I suspect one of the resistors/capacitors on the underside of the board went wrong :/

 

One of the leaky capacitors might have ruined a trace. That's likely the source of all your problems.

 

Very likely, but after 3 afternoons looking the entire board and reflowing/resoldering components i didnt see nothing brinken or eaten by the capacitor´s leakage.

Shame on me!

 

You may not see a thing and that makes it a huge PITA. You'd have to check each trace under a magnifying glass and ideally with something to check for continuity.

Beats the hell out of having the gears misaligned on my SegaCD1. The laser won't raise/lower with the tray properly anymore. :/

 

Don't get discouraged, friend ! Keep trying !

 

Im lost with this

Maybe there is any leg of the sanyo chip to "force" the system to see the cds as data instead of audio?

 

Not in the least.