Sega Genesis recapping and stuff

[UraBahn]

Hi everyone, it's been a long while but I've been very busy what with my job and with my hobby. Learned a *lot* since I last posted here, I also found out what happens when you increase the uF value of a capacitor in a circuit too high (it often ain't pretty.) Learned that too low ESR can be undesirable in some circuits as well. Also I pay a lot closer attention to permissible ripple current and ESR, etc. now better than ever before.

Bleh, enough about my misadventures, onward to the good stuff...

So I got a bunch of Sega Genesis systems, all of which had some pretty nasty old caps. The better ones were Rubycon and Shoei, the worst... Chhsi. *shudder* Got a VA3 Model 1 which had some rainbow banding and lousy color saturation onscreen and some of the muddiest, muffliest sound imaginable. Replaced the caps near the CX1145 encoder and the picture cleared up nicely. I then replaced the 10uF (way too freaking high!) decoupling caps near the sound circuit with 1uF metallized polypropylene films, though for the YM2612's outputs I used 0.22uF films. These *tremendously* cleared up the high end, but sacrificed some of the bass. (I'll try 0.33uF on another VA3~6 later, but for now these are fine.)

Also got a hold of a VA3 Model 2 (the 2/3 motherboard revision) which had the rather unfairly maligned KA2195 encoder. You know what to expect from stock systems using the KA2195: jailbars, pixellation, lousy color, etc. After replacing the vintage Rubycon/Shoei caps with new Rubycon YXG/ZLH and Chemicon KY and increasing the 47uF grounding caps to 100uF, the jailbars have almost completely disappeared and the color is much better, though there's still a little bit of pixellation - that can only be 100% fixed by disconnecting the KA2195's XTAL IN pin from the motherboard and running it to a 3.58 MHz 4-pin can oscillator, as described here:
https://bitsandblips.wordpress.com/2...-video-encoder
You'll notice that, after it's cleaned up, the KA2195's picture quality is actually _far_ better than the fan-favorite (stock) CX1645: very sharp for RF, absolutely zero rainbow banding/fringing, bright and vivid colors.

Thank goodness the 2/3 motherboard revisions have decent enough sound as-is so no replacement audio output logic is necessary (unless you really like > 32 kHz squeals from the FM tearing gaping holes in your eardrums), though replacing the 10uF audio left/right/mono caps with 1uF metal films seemed to help the treble response very slightly.

Alright, time for bed.

[Heihachi_73]

Re: Sega Genesis recapping and stuff

Sort of on-topic, is there any way to improve the yellow artifacts in a PAL VA0 Mega Drive II? My other MD2s do not have this problem; the "PRODUCED BY OR UNDER LICENSE FROM SEGA ENTERPRISES" text is the most notable part where the yellow seeps through. IIRC it has nothing to do with rainbow banding on the early model 1 consoles (all of my consoles all have the same Fujitsu MB3514 video encoder). No complaints about the sound in all three systems.

I also have a non-working VA1 model 2 - no matter what game is inserted, even when putting a Mega Key between the games and the console I get either a black screen or rarely a red screen. The pins are spotless and I can't find any noticeable problem on the board. All of my working consoles have either Rubycon or Shoei caps too; this one however has Nippon Chemi-con caps except for a sole Nichicon at CE12 (can't complain here either).

I have had four Mega Drive IIs - VA0, VA1 (recently sold), VA1 (not working) and VA1.8 (bought as "not working/parts" but works perfectly)

[stj]

Re: Sega Genesis recapping and stuff

being blunt, i dont care if the caps are made by god - they are over 20years old.
replace them - and use low esr ones near the video encoder if not everywhere.

[Uranium-235]

Re: Sega Genesis recapping and stuff

if you own the game, use an emulator with sharpening plugins

[Heihachi_73]

Re: Sega Genesis recapping and stuff

Using an emulator over repairing an original console is cheating.

I resurrected two Mega Drive cartridges from the grave last night using the resistor-to-ground trick. The first "dead" cart was Columns, repaired using a 390Ω resistor pulled from my stockpile of pulled parts (mostly from failed PSUs and TV boards), and the second was Arnold Palmer Tournament Golf, using the only 330Ω I had on me at the time. More details on cartridge resurrection can be found over at Sega-16.

[UraBahn]

Re: Sega Genesis recapping and stuff

being blunt, i dont care if the caps are made by god - they are over 20years old.
replace them - and use low esr ones near the video encoder if not everywhere.

Well, don't use _too_ low ESR caps on a Genesis, otherwise you might wind up increasing the ripple in areas you really don't want to. I wouldn't recommend anything lower ESR than Chemi-con KY, Rubycon ZL or Nichicon PM in a Genesis. (Yes, I know I used a ZLH somewhere but it was what I had on hand... fortunately it doesn't seem to be doing anything bad. Yet.)

[UraBahn]

Re: Sega Genesis recapping and stuff

Sort of on-topic, is there any way to improve the yellow artifacts in a PAL VA0 Mega Drive II? My other MD2s do not have this problem; the "PRODUCED BY OR UNDER LICENSE FROM SEGA ENTERPRISES" text is the most notable part where the yellow seeps through. IIRC it has nothing to do with rainbow banding on the early model 1 consoles (all of my consoles all have the same Fujitsu MB3514 video encoder). No complaints about the sound in all three systems.

Alas I am not familiar with the Fujitsu MB3514 or PAL systems, but yellow bleed-through could be a sign of a noisy or drifting colorburst clock (which is what plagues the KA2195 in NTSC systems.) You could try replacing the caps near the video encoder (and especially every cap that filters 5v to ground.) You can replace 10uf with 22uF and 47uF with 100uF in most cases and get slightly better performance, but don't push it too high from its original value (I once replaced a 10uF with a 100uF, and was horrified to have the system wait 5-6 seconds just to display the TMSS screen!) If the colorburst clock is drifting, then it might be time to replace the main oscillator as the colorburst clock is (likely) divided from it.

I also have a non-working VA1 model 2 - no matter what game is inserted, even when putting a Mega Key between the games and the console I get either a black screen or rarely a red screen. The pins are spotless and I can't find any noticeable problem on the board. All of my working consoles have either Rubycon or Shoei caps too; this one however has Nippon Chemi-con caps except for a sole Nichicon at CE12 (can't complain here either).

An (occasional) red screen indicates that the 68000 is working but something is keeping it from properly check-summing the game. I'd touch up the soldering on the cartridge slot pins all the same, even if they look fine. I'd also try a cleaning cartridge or a little Brasso on a q-tip on the metal fingers in the cartridge slot as well (clean with isopropynol.) In addition, I've ran into hairline cracks on traces (particularly on a Master System I was reviving) which looked absolutely flawless to the eye, but wound up requiring me to jump with a length of wire.

A _very_ low possibility would be that one of the RAM chips had failed, which would be quite tragic on a model 2 as they are usually surface-mount soldered to the board. I had a VA6 Model 1 that had a dead Z80 RAM chip, which displayed the TMSS screen fine before locking at a black screen. (Most games will busy-wait the Z80 for a response just before the SEGA logo, but if the Z80 isn't working, they'll be busy-waiting forever.)

[stj]

Re: Sega Genesis recapping and stuff

none of that's a probem, just pull the ram - put it on a carrier and test it.

[UraBahn]

Re: Sega Genesis recapping and stuff

For reference, the RAM memories in a Genesis are either PSRAM or SRAM, but both are accessed/tested the same way (test as SRAM.) The only DRAM in the system is the video memory, and that's VRAM (dual-ported.)

[Logistics]

Re: Sega Genesis recapping and stuff

Interesting that this came up. When you're done getting it up and running the way you want, I'd suggest heading over to gamesx.com and looking up info on running pure RGB out of the Genesis (and other consoles), and find yourself an old-school Commodore monitor that can accept the signal or something similar. The picture is very clear when using RGB, but this could be a bad thing if, like Nintendo, you prescribe to the blurred, softened image rather than sharp pixels.

Good read, by the way. I recapped my Playstation, years ago and cleaned up all connections with some Deoxit. Always, keep it around as well as my beloved Dreamcast, which I went to recap, one time but the capacitors were all UCC's and Nichicon if I recall correctly. And not that they could have had more appropriate model lines of said brands' capacitors installed, but they weren't garbage like the ones in the Playstation.

[Heihachi_73]

Re: Sega Genesis recapping and stuff

I recently hacked up a PAL model 2 VA1.8, but gave up because I couldn't be bothered making a small circuit to get color in NTSC mode! It plays at the right speed (60Hz) but in black and white due to the wrong frequency (it's trying to output a PAL signal at the wrong frequency due to the same crystal being used, and failing miserably - it's not PAL60, not NTSC, but a completely screwed-up nonsense mode of PAL). Of course, I can still jumper it back to 50Hz again but I would rather get it right before doing anything to it so I can actually switch between the two while the game is running, as some games refuse to run in the "wrong" region (see below) - it's no loss since it was just a spare PCB, not a complete unit.

The console is definitely region-hacked to "NTSC" now, as Megaman: The Wily Wars shows a message that it is not designed for this console - but of course it magically works by booting the console in PAL mode then disconnecting the jumper wire after the Sega/Capcom logos. Yes, I risked a genuine $600 game just to play it at full speed. In black and white.

@ Logistics:
Garbage caps in a PlayStation? I've only ever seen Nichicon or Panasonic caps in there - even the power supply boards have the Nichicon or Matsushita "M" logo on them. Unless of course you mean the system board, as I have never touched the caps there, nor have I seen any bad/blown/leaked ones.

[Logistics]

Re: Sega Genesis recapping and stuff

I think it may have just been the model line of capacitors which were in there, which were simply a budget model. Don't get me wrong; it's very possible that it was an adequate line of caps to power it, but my Playstation had been sitting idle for years, and I felt it was time for a refresh, and I wanted to use something better than budget.

Yes, I recapped that PSU--I wouldn't want to mess with all the surface-mount stuff on the main-board.

[stj]

Re: Sega Genesis recapping and stuff

i work on arcade versions of the psx, and usually replace the smd electrolytics with tantalums.

[Heihachi_73]

Re: Sega Genesis recapping and stuff

Arcade versions of the PSX... Tekken Tag would be a nice addition to my living room, if it didn't cost as much as a car.

[stj]

Re: Sega Genesis recapping and stuff

hmmm

got 1,2 and maybe 3
dont think i have tag.

also got virtua-fighter 3
(pcb's - not cabs!)