Aiwa Mega CD CSD-GM1 Mainboard Repair

Where to begin... Picked up those two Aiwa Mega CDs that were on eBay in an essentially non-functioning condition.
Of the two units, one was heavily damaged and I have been patching up the cracks in the PCB slowly.



Below are the two voltage regulators I've been having a look into. They are the same on both mainboards.
However the voltage outputs are significantly different when used with each others transformers.
One looks to have been repaired / replaced in the past as the stand-offs on the case do not fit it.
The other looks to be the original as it fits snug as a bug.
But any ideas as to why B1064 would be outputting two very different values?





==================================
01-01 board with replaced tranformer
B1064 - 5.6
- 5.5
- 5.0
7806A - 0
- 0
- 0
==================================
01-01 board with unrepaired transformer
B1064 - 19.2
- 8.5
- 19.7
7806A - 0
- 0
- 0
==================================
02-01 board with replaced tranformer
B1064 - 5.7
- 5.7
- 5.0
7806A - 5.9
- 0
- 8.75
==================================
02-01 board with unrepaired transformer
B1064 - 19
- 8.5
- 19
7806A - 6
- 0
-12
==================================
Another thing I noticed is that;
Power on LED connector reads 19V on unrepaired transformer and lights up OK.
Yet the power on LED connector reads ~5V on repaired / replaced transformer and does not light up.

Pictures of the two units
https://picasaweb.google.com/101985214970836533590/AiwaMegaCDCSDG1MUnit01?noredirect=1 - Revision 1
https://picasaweb.google.com/101985214970836533590/AiwaMegaCDCSDG1MUnit02?noredirect=1 - Revision 2
https://picasaweb.google.com/101985214970836533590/AiwaMegaCDCSDG1MUnit01GameUnit?noredirect=1 - Game Unit (1 of 2)
https://picasaweb.google.com/101985214970836533590/AiwaMegaCDCSDG1MUnit02GameUnit?noredirect=1 - Game Unit (1 of 2)
Any ideas on where I should be looking? My brain is fried after all that soldering and watching The Avengers.

Edit: Here's the capacitor values for anyone interested - http://retrojunkie.net/guides/sega/0007.php

 

What do you mean with "replaced" and "unrepaired" transformer in respect to the two different voltage regulators? Is this transformer on a separate board, and this voltage regulator part of that, or is it all integrated on one of the main boards?

 

you got a really big project there.

 

Ah transformer is separate tucked away in the back of the unit. It's huge and hard to miss yet I've taken no photos of them yet.
One of the Mega CDs looks to have had the transformer replaced in the past as it seems to be wedged in.
I tested the voltage regulators on both boards (01-01 and 02-01 - markings on the boards) with both transformers and they've given very different readouts.

You are telling me! You should see my workbench - nothing is going to be repaired there for a while!

What is this B1064 IC though? I can't find much information on it, at least when compared to the 7806A.

 

Ah.. are there any part numbers on these transformers? Do they both output the same alternating current? And the last (stupid) question, you are feeding them with 100vac by using a stepdown transformer?

 

Progress!







Looks like some of my fantastic wiring actually worked.
The Mega Drive section mostly works. CD laser needs replacing and Mega Drive sound is tinny, very very tinny.
AM / FM Radio doesn't appear to have any sound - Might just be really, really quiet.
I thought there was no sound through the internal speakers and earphone jack - I was wrong!
There is sound there but it is extremely quiet, as in you-need-to-be-in-front-of-the-speakers-in-a-quiet-room quiet.

One step closer, still need to work out the voltage irregularities between the two units if possible.
The one that was sold as working / partially functional freezes sometimes apparently - that could be a voltage issue right?

No part numbers on the transformers that I can see, pulled them out and had a look but nothing.
Both are 100V rated at 20W and are 12V DC too if anyone wants to send me some C cell batteries?
I certainly am using a step down transformer to take it from 240V -> 110V. Without it... smoke and char :grief:

 

Great progress! According to this:

http://pdf1.alldatasheet.com/datasheet-pdf/view/271798/SAVANTIC/2SB1064.html

That B1064 is probably part of the audio amplifier circuit, so no suprise the audio isn't working (correctly).

 

I might just check some of the voltages that enter the unit from the transformer in the 01-01 board (that's the one with the repaired / replaced transformer in it).
15 minutes later and the Mega CD 2 music (as quiet as it is) is starting to drive me insane.
At least the unit hasn't caught on fire... yet!

Edit: Well I'm getting 5.5V on one of the random points labelled as 8V on the "working" (01-01 board) Mega-CD 2.
I'll check what the "broken" (02-01 board) has to say on that same point.

 

Yes, you should check if both transformers are delivering the same current to rule out any problems on that side. I would also recommend to desolder both regulators and measure/compare the voltage on the base connection of both boards. To check if it is really part of the audio amplifier you might want to connect something like a headphone to the collector leg to check for the soft audio signal. Where are the unit's speakers connected to?

 

Speaker connector squared off in blue. To the right we have 7806A and below it we have B1064.
Earphone jack is immediately to the left of the speaker connector.



The "working" 01-01 Mega CD

CN602 - TO CD GAME
DG - 0V
+5 - 4.83V
AG - 0V
R - 0V
L - 0V

CN601 - TO CD BOARD
Vcon - 4.5V
8V - 5.4V
DG - 0V
R - 0V
AG - 0V
L - 0V

CN802 - TO DECK
1 - 5.4V
2 - 10.7V (Drops off)
3 - 10.7V (Drops off)
4 - 0V

CN501
L-in - 0V
R-in - 0V
GND - 0V
L out - 0V
R out - 0V
B+ - 5.4V

Speaker Connector
1 - 2.43V
2 - 2.54V
3 - 0V

TO POWER INDICATOR
5.43V
----------------------------------------------------------------------------------------------------------
"Broken" 02-01 Mega CD


CN602 - TO CD GAME
DG - 0V
+5 - 5.6V
AG - 0V
R - 0V
L - 0V


CN601 - TO CD BOARD
Vcon - 5.2V
8V - 8.5V
DG - 0V
R - 0V
AG - 0V
L - 0V


CN802 - TO DECK
1 - 18.8V
2 - 11V (Drops off)
3 - 11V (Drops off)
4 - 0V


CN501
L-in - 0V
R-in - 0V
GND - 0V
L out - 0V
R out - 0V
B+ - 8.5V


Speaker Connector
1 - 9.5V
2 - 9.5V
3 - 0V


TO POWER INDICATOR
18.6V

 

Uh oh, the "working" Mega-CD unit no longer seems to do anything... and the "broken" one is still working.
Since the power light on the darned thing never seems to work, I can't tell if it is getting power or not without probing the point on the mainboard with a multimeter.

Speaking of probing, how do I go about probing the transformer?
I would have assumed that the connector for power would have been a good place to start...
The wiring from the top to bottom of the following picture is blue, blue, black, red, white, white.



Yet they all read 0 when checking them - assuming ground is the black cable, right?

I also tested with the damaged CD deck and it seems to pass through power to the Mega Drive section perfectly.
Phewf! Glad that wasn't smoke and flames!



Edit: It's all about load isn't it? (I never did electronics in school :biggrin-new These were pulled from the "broken" functional Aiwa Mega-CD unit.

02-01 repaired board (snapped) with presumed original working transformer
Blue: 9.75V
White: 6.30V
Red: 20.75V
Black: 0V Ground


01-01 board (non-snapped) with presumed original working transformer
Blue: 9.05V
White: 6.17V
Red: 18.95V
Black: 0V Ground


01-01 board (non-snapped) with original transformer (bodgily repaired)
Blue: 2.6V
White: 4.5V
Red: 5.5V
Black: 0V Ground

The 7806A requires more than 6V to power up and zap around electricity right?
That's a good reason for it not to work.
I'll have to rig up some sort of internal / external power supply unless anyone can suggest a transformer that would fit?

We're at the end of the weekend now, so any suggestions for through the week are welcome!
Here's the current (must resist pun) state:

01-01 - 5V line to the CD GAME does not have any voltage at all - this needs to be repaired.
- 7806A has 0 with known good transformer installed.
- Needs to have the dodgy transformer replaced.


02-01 - needs to have the sound circuits repaired somehow - transistors / caps - something.



Thanks for your input (ughhhh more puns) too Dutchy!

 

Voltage output on the transformer stabilizes when load is applied to it, but within the specified range ofcourse. When one of the boards has a short somewhere, the voltage can drop below the intended value. I would start to measure the output of both transformers without anything connected to it, the easiest way to do this is to measure every combination of wires and write it down.

You have blue(1), blue(2), black, red, white(1), white(2) - so you start with your multimeter set to ac with:

blue(1) - blue(2) // blue(1) - black // blue(1) - red // blue(1) - white(1) // blue(1) - white(2)
blue(2) - black // blue(2) - red // blue(2) - white(1) // blue(2) - white(2)
black - red // black - white(1) // black - white(2)
etc, etc

When you write everything down in columns it should be obvious when comparing the two transformers, what the function of the wires is.

Ideally the input is 2 volts above the 6 volts output, its probably part of the stabilizing circuit after the ac to dc conversion.

Link for the pinout: http://pdf1.alldatasheet.com/datasheet-pdf/view/4452/MOTOROLA/MC7806AC.html

 

Does Aiwa Mega CD have region jumpers like normal Megadrives?

 

Great stuff !

By the way, open the digital part and inspect for leaking capacitors.


The drive has missing a big chunk of the board... Do you have that piece ?

 

Why didn't I think of this earlier? C cell batteries! Bypass the transformers all together and test the voltages running off batteries!
Maybe even one of my DC-DC stepdown circuits wired up to the terminals should do the job. Why does it have to be Monday though?
Now I can't touch any of this until next weekend... grumble grumble.

2 volts about 6 volts for the 7806A, got it. Sounds the same as that DC-DC stepdown I have. Hope I've got a 14V or more PSU lying about though.

It should have the region jumpers, I did take one of the Mega Drive units apart to check for any visual damage but wasn't able to see any.
And don't worry I have that giant triangle of PCB, it was just rattling around on the inside. So there is hope yet.

I wonder if battery mode will power the Mega Drive section though...

Edit: Nope, no power to the Mega Drive section running on 12V battery mode - tested with both units.
Maybe it does need ~20V to give it enough juice, or maybe the battery section doesn't wire in to the Mega Drive section at all.







Just checked and found the blue and white have no juice running to them at all, maybe those DC-DC converters will come in handy.
I can easily feed in 9V and 6V to to blue and white respectively from the DC-DC adjustable converters.
Anyone think I should increase the main voltage along red to 20V or just leave it at 12V while testing?

 

I think you should leave it at the same current the original batteries would give. Raising it above spec will probably damage or wear out some components, and the megadrive part probably isn't wired in anyway (just like the multimega/cdx).

 

May I say well done for giving this repair a go! I think I would have started crying after "simply....."

 

Multi-Megas are rubbish, they don't have cool features like AM radio and tape deck built in (Just kidding I love my Multi-Mega - it's so small!)
Looks like that is the way it is though.
Only question is though, if I do wire them in and we are going off the 12V for the red instead of the 20V off the transformer... how can I trust that the 6V and 9V values are correct?
I think I need to have a look at the paths they run, that 7806 should be fed something around 8V right to output at 6V? So if the 9V runs into it, then we should be good right?

Hahaha thanks! I suppose the condition it was in couldn't really get any worse so there wasn't too much to lose.
Looking forward to getting back to it this weekend. Why does the working week have to interfere so much.
That said, here's the video I took after feeding in the 12V from a random power pack I was going to use for the Saturn external PSU project that I scrapped a while back.
Thankfully I have those DC-DC stepdown converter boards left over that should be very useful for getting 6V and 9V out of and since the PSU is 4 amps, it has plenty of free power for it!

 

Alright back again with another update.

Started off by joining the two blue (blue->blue) and two white (white->white) as they were separate for reasons unknown.
They both feed into the board and supply voltage from the known working transformer, so they both needed to be connected - possibly on different rails?
The ugly wires hanging off to the left are redundant and will eventually be removed - they used to run to the transformer and AC inlet.



Next up we have the DC-DC stepdown converters attached. One is tuned to 6.3V and the other 9.75V.
Ground is wired up to the same point on the battery PCB that feeds off into the black transformer in the background via the socket.



Here's the Mega CD deck with the grey cable that runs to the Mega Drive / Mega CD section that sits underneath the Aiwa.
There are three connectors that join to this board.
1. A long connector on the right hand side (not in the shot) that powers the CD drive and front control buttons (play, skip, etc).
2. The medium sized left connector which has 8V running through one of the pins.
3. The shortest connector on the right that provides 5V to the Mega Drive section.
I found that the 5V was reading only 3.3V and providing the poor image that is coming up soon (hang tight we are nearly there).
The 8V rail was reading with no issues at all.



Here's an overview of the mess with the power connected in. The unit sits upside down and back to front for everything to connect.
You can also see we are using the mainboard that was heavily damaged with my fantastic patch up job (if I do say so myself).
The working transformer can be seen in the background still installed.



The back of the unit is our next image and shows the two DC-DC converters connected to power.



Blue, white, red and black are the colours of the day. I am pretty well acquainted with where they run to on the mainboard now.



Now to power the unit on and ... errr, that's not looking quite right...



So I measured the voltages on various points. All the points that ran from the external PSU to the mainboard were the same as the assumed working transformer (uh-oh).
I checked the CD deck voltages out of the two pins and found that one was spot on and the other was too low by almost 2V.
Checked the 6V voltage regulator and found that it was only outputting 4V. For a 6V regulator I could tell that was not quite right.
So I tried disconnecting one of the DC-DC stepdown converters to see which one provides the Mega Drive with power.
Sure enough it was the white wires running from the mainboard that are fed through to the Mega Drive.
No idea what blue does at this point, but I think it is likely CD circuitry for the Mega CD (more tests to be done on that one yet!)



Now if you'll remember for a moment I was feeding 6.3V to white, 9.75V to blue and 12V to red... you can see we have a problem.
I was feeding 6.3V to a voltage regulator that is meant to output at 6V.
Impossible mission? Yes! So I tweaked the pot up to 8V to test...



Not only was the picture a million times better, THERE WAS ALSO SOUND off the DAMAGED MAINBOARD.
While this is great news, it means that the dodgy looking transformer is rubbish (and now in the bin) and the working one is failing.
As it only outputs 6.3V to the white power cables... I think I'm in trouble.

That aside though, victory! I've got a new laser for the CD deck so I might even get a chance to play a Sega Mega CD game.
And thanks again to Dutchy for reminding me about voltage regulators requiring more than they output. You may have saved the day!

 

Both transformers broken? You've got to wonder what they did to those poor aiwa devices to get them in this state. Good to hear the sound is working, but i still see some pixelation/noise on the last screenshot so i guess there is still something not 100% ok with the power?