VOGONS


First post, by Chances

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Hello, bit of a long story so ill say thanks in advance 😀
I was lucky to get my hands on a MegaPC yesterday with a slight problem im hoping to fix up.
The problem is when trying to use the megadrive, the game loads up, music starts but no picture. The PC was supposedly working 100%.

So last night I got it home and plugged it all up and as expected the megadrive seems to load the game but the screen just flashed for a moment when the cart was booting but then blank... fair enough.

I switched it over to the PC and eventually figured out the correct hard drive specs to punch into the BIOS and up and away she went. Booted up golden axe for dos, great picture and sound.

Later that night (very late) I checked the megadrive cart again and I suddenly noticed that the image is actually there but just completely dark... but it was there! Better than no picture at all I figure.

So today I went down to the electronics shop to grab all the capacitors for everything and proceeded to swap them over during the afternoon and into the night.
Firstly I worked on the motherboard, the battery had already been removed by the previous owner and there was some damage to the PCB which I spent some time trying to clean up. I also checked the tracks and they all seem to be ok - perhaps I did not check them properly?
There were two diodes which looked in bad shape, I measured them and they seem to still be somewhat ok... I tried to hit them with the soldering iron to freshen up the pads but I gave up shortly after to just concentrate on the capacitors to start with.

Once the motherboard was re-capped I plugged everything back in and crossed my fingers. Well still worked which was a plus but had the same problem with the megadrive side of it.

Back to the shed to recap the sega card and the riser as I spotted caps on there also.
Did all of them, put it back together, no smoke but still no go with the screen 🙁

I did notice now that when I have a game cartridge in and playing, if I switch over to the PC side I can - for a split second - see the color image of the megadrive game before it flicks over to the DOS screen. I can switch back and fourth over and over and its there !! ... but only for a moment.

So its 2am now and im about to put on a CRT repair video while I go to sleep so I dont zap myself tomorrow when I take it apart 😁

I think that perhaps when the monitor gets the signal from the megadrive and changes its refresh rate over that there is an issue with all that inside the CRT ?

Im mostly basic with electronics, im confident soldering but changing caps is about as fancy as I get.

Sorry for the long post. I have some pictures of the effort so far. The boards before and after my butchery 😉
The damage I cleaned up on the PCB.
Golden AXE working under DOS - so the screen works great, was hoping that I wouldn’t have to open it.

Hopefully somebody can suggest something simple I may have missed or something I can try before doing the re-cap on the CRT.

Anyway thanks again for reading and looking forward to hopefully getting this PC going!

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Reply 1 of 12, by keropi

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oh another mega-pc owner! welcome to the club 😀

the only suggestion I have is to ask if you have you checked that the monitor vga cable and the ribbon-cable that connects the megadrive card to the motherboard are OK?
maybe there is a break and it causes this issue...
I can see some bowing on the golden axe screen , maybe a recap will help this monitor... but keep in mind that it's pretty low-quality to begin with 🤣 and actually shipped from the factory with horizontal linearity issues in megadrive mode... since you are recaping it replace C521 with a 2.2uf/200v one to somewhat improve the situation:

HUijPCRh.png

also that fat trace in the battery area will surely need cleaning and at least tinning with solder to restore it
and another suggestion , those new caps you have installed do not inspire confidence - you should try and get some nice japanese ones for this machine, like nichicon, rubycon, chemicon, panasonic etc

Last edited by keropi on 2021-02-15, 19:43. Edited 1 time in total.

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Reply 2 of 12, by Zalog

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Welcome to the club from me too!

Aside from checking the cable (and it's properly connected) as keropi suggested which is usual source of problems, the only things I can suggest are:

1) ensure that the mega drive card is properly seated into the cartridge/front plate pcb connector (and the connector is clean) - dirt here can cause issues.

2) if all else fails, check the switch on the front plate plate isn't on its way out. They are fairly tough and I haven't seen one fail yet, but it's possible, and you seeing the screen momentarily on switching sides is suggestive. If you remove the plastic front cover you can manually move the switch to see/feel if there are any obvious problems.

Hope this all helps and good luck 🤞

Reply 3 of 12, by Chances

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keropi wrote on 2021-02-15, 19:09:
oh another mega-pc owner! welcome to the club :) […]
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oh another mega-pc owner! welcome to the club 😀

the only suggestion I have is to ask if you have you checked that the monitor vga cable and the ribbon-cable that connects the megadrive card to the motherboard are OK?
maybe there is a break and it causes this issue...
I can see some bowing on the golden axe screen , maybe a recap will help this monitor... but keep in mind that it's pretty low-quality to begin with 🤣 and actually shipped from the factory with horizontal linearity issues in megadrive mode... since you are recaping it replace C521 with a 2.2uf/200v one to somewhat improve the situation:

HUijPCRh.png

also that fat trace in the battery area will surely need cleaning and at least tinning with solder to restore it
and another suggestion , those new caps you have installed do not inspire confidence - you should try and get some nice japanese ones for this machine, like nichicon, rubycon, chemicon, panasonic etc

Hello keropi and thanks for the reply, I have studied all your MegaPC posts before joining 😀 Honored to have you reply haha 😁
Oh those caps... yeah I knew when I got them from the local shop on Sunday that they were probably some of the worse available and I felt REALLY bad soldering them in. Once I get it working I will order up some high quality caps and give it the components it deserves.

I opened up the CRT today and it looked a little too scary for me to be poking around, I took a detailed video of most the components and everything looks ok visually. Id feel much better getting someone with the right safety equipment to at least pull out the PCB for me so I can replace the caps in my own time.
I had a chat to a local electronics repair guy today who does alot of CRT's. He seems to think the screen itself is fine because the PC side of it is working.
I think ill leave it for now and get those traces fixed up properly first.

I did touch and poke the ribbon cable while it was running to see if I noticed any glitches in the screen but nothing. Same with the VGA cable, moved around both ends and it made no difference what so ever. When I disassemble it again shortly i'll check over that ribbon cable and just make sure its not faulty itself.

Zalog wrote on 2021-02-15, 19:37:
Welcome to the club from me too! […]
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Welcome to the club from me too!

Aside from checking the cable (and it's properly connected) as keropi suggested which is usual source of problems, the only things I can suggest are:

1) ensure that the mega drive card is properly seated into the cartridge/front plate pcb connector (and the connector is clean) - dirt here can cause issues.

2) if all else fails, check the switch on the front plate plate isn't on its way out. They are fairly tough and I haven't seen one fail yet, but it's possible, and you seeing the screen momentarily on switching sides is suggestive. If you remove the plastic front cover you can manually move the switch to see/feel if there are any obvious problems.

Hope this all helps and good luck 🤞

Hello Zalog and thanks for the reply !! 😀
It was interesting to say the least when removing the sega card from the pc, one of the more odd ones ive encountered.
That front connector looks good and ive re-seated it twice but with no change unfortunately.

I have been testing it without the front cover so im physically moving that switch from side to side. I tried to record a video in super slow motion but gave up as the moment was too hard to capture 🤣... I settled for just normal slow motion which at least captured the cart screen for a frame or 2.

Im hoping that fixing those traces will help, thats the next most obvious thing.
To me the video seems to show that the screen flicks over to the sega but perhaps something which needs power to boost the signal isnt there so its super dull??
Just thinking off the top of my head here... but anyway here is the video. I will dismantle it all again (getting good at it now haha) and check over all those traces around the battery leakage.

The PSU looks to be never opened either. I may open it up and at least give it a look over and blow away all the dust and crud I can see through the fan.

Back to the garage !
By the way I love the sound the switch makes in slow motion, it sounds like a huge power breaker 😎
https://www.youtube.com/watch?v=GRTh2KyjPoY

Reply 4 of 12, by Chances

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Oh my god ... its working ! 😀
It was that really bad looking trace on the board. Wasnt much left of it after I started to scrape back the gunk but I thought I would give it a quick go with some wire I had laying around before getting too carried away with anything else. The repair itself needs to be re-done with some better wire I think, but for now I will enjoy the system for a while ! 😀
The video quality reminds me of my Amiga 500 on the original Commodore CRT, very nice!

Ill be sure to keep the thread up to date in the future and show some more photos as time goes on of any more updates - so happy !

Now I need to get the mouse working... Just software I imagine so not too worried about that, worst case it cant be any harder than the mainboard repair ! 😀)

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Reply 5 of 12, by keropi

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great!!!!! so it was that fat trace (probably the 12v line if I had to guess), nice! enjoy!
the screen is REALLY good on megadrive mode - just that compression it does on the right side is annoying (at least to me) so if you do one thing on the monitor then just replace C521 😉

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Reply 6 of 12, by Chances

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keropi wrote on 2021-02-16, 07:53:

great!!!!! so it was that fat trace (probably the 12v line if I had to guess), nice! enjoy!
the screen is REALLY good on megadrive mode - just that compression it does on the right side is annoying (at least to me) so if you do one thing on the monitor then just replace C521 😉

Aww yeah 😀
Honestly I havent noticed the right side yet - my other sega is on RF to the tv so the quality is pathetic compared to this.
I might get the CRT down to the repair guy one day and get him to change that C521 it for me once it starts to annoy me.

What I do notice is the edges curving inwards slightly on the left and right but just enjoying the system at the moment so its easy to ignore.

I think ill get a new fan for the PSU is next or at least see if I can lube this one up a little. PSU is probably quite well aged at this stage so we will see if it holds up to my thrashing 😁

Also need to sort out some way of getting stuff onto the hard drive. Perhaps one of those geotek usb emulator drives might do the trick.
Would be nice to run some software other than whats on the drive although there are some games on here I havent played in a long time 😊

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Reply 7 of 12, by keropi

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I think there are pots inside the monitor to fix this - but I don't remember for sure...
here is the service manual and the monitor schematics with better quality, could be of help: http://www.mediafire.com/file/xux0fvv3z11tdf1 … -scans.zip/file
page 25 has alignment instructions

🎵 PCMIDI mpu site buy+info
🎧 WIP Orpheus soundcard site
💻 WTB Amstrad PC7486SLC-33 system

Reply 8 of 12, by Chances

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keropi wrote on 2021-02-16, 10:35:

I think there are pots inside the monitor to fix this - but I don't remember for sure...
here is the service manual and the monitor schematics with better quality, could be of help: http://www.mediafire.com/file/xux0fvv3z11tdf1 … -scans.zip/file
page 25 has alignment instructions

I did see the pots but I'm too scared to power the CRT up without the cover 😁

PS2 mouse still wont detect, have tried a few drivers, cutemouse and some dos versions before and after 6.22 with no luck.
Could be more damage on the MB, ill spend some time today trying to get it working in software but the BIOS doesnt detect any PS2 mice so could be the mouse itself or the board.
Will delve into the PS2 issues today....

Got the gotek working, wow took all day... Now im having space issues with the hard drive, im not used to 40mb hard drives at all, Monkey island takes up like 15% of the damn drive !!

I did find a serial mouse for $10, waiting for the seller to get back to me, would be nice to try that also just incase the PS2 issue is hardware.

Looking into CF hard drives, so much info out there its kinda overwhelming.
I think I will order up an XT-IDE from ebay (picture attached).
Although it says this in the details - "It also works in 286 and up, but the Monotech DoubleROM card will provide you better performance in those."

I tried looking for these Monotech DoubleROM cards but couldnt find them.

From my understanding these cards have an optional BIOS ROM slot which will bypass the stock BIOS to allow bigger hard drives and a bunch of other goodies... ?
Also that you can insert a ROM into a network card or some other card which has the BIOS spare slot and the option to boot from it ?
Hopefully im on the right track ! 😀
I think just to keep things simple for me I will stick to an official XT-IDE card and pay the little extra for it.

Looked into the VRAM upgrade but they seem hard to find locally and postage from overseas is worth more than the chips themselves 🙁

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Last edited by Chances on 2021-02-18, 02:38. Edited 1 time in total.

Reply 9 of 12, by Chances

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Just got an idea but I dont want to just try it before checking its not going to damage anything...

On the MB there are 2 headers for Mouse and KB - one is just a grey ribbon cable and the other has many colors.

If I was to plug the mouse cable into the KB header and vise versa for the KB into the mouse header - it might show me if its the mouse or the mainboard with the issue.
Just not 100% sure the cables match so I dont want to just slap them in and power up.

Ill check through the schematics shortly but its so blurry and hard to read it might just be a waste of time.

Just throwing my thoughts out there, hopefully someone knows for sure that this wont damage anything if I try....

Cheers! 😀

Reply 11 of 12, by Chances

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megatron-uk wrote on 2021-02-18, 09:05:

You can't (normally) plug a PS2 mouse in to a keyboard port and vice-versa, so that won't help to test which is faulty.

I meant swapping the cables inside from the ps2 headers to the motherboard, then connecting them in reverse... just to check from the ps2 connector to the MB header.
Ive given up on that idea for now, making do with an old joystick I had tucked away and its working great.
I have a NOS ps2 mouse on order and trying to hunt down a serial mouse - surely one of them will work.

Reply 12 of 12, by keropi

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you can swap the ps2 headers without issues so you can try if the keyboard will work when connected to the mouse connector
could be a wire issue

🎵 PCMIDI mpu site buy+info
🎧 WIP Orpheus soundcard site
💻 WTB Amstrad PC7486SLC-33 system