Issue With Yeno SC3000 Board

[mutantcamel101]

I may have video display problems on my Yeno SC3000 I might have a dry solder issue with the video pins and the board. Shame they removed the rf modulator on the French model as I wouldn't have attempted to open it up.

I have attempted to take it apart, but I believe I might have to desolder the power switch but I'm unsure how to remove the small video board. The board also looks like it's glued to the main board maybe

There are 3 little plastic knobs which I thought were screws named VR 1 2 and 3 I tried turning them and it looks like the plastic is brittle and started to break when I turned them. I'm not sure if I'm broken something important. One of them has a number 471 4312. I'm seriously worried now, are these voltage regulators? No idea if they can be fixed or replaced.

Anyone else have a Yeno hard key version who could give me some advice please.....

 

[mutantcamel101]

I'm not sure if these knobs adjust the color and contrast. I am struggling to find documentation on the Yeno to confirm what VR1 2 and 3 do on the video board.

 

[mutantcamel101]

**Edit** I managed to remove the video board by squeezing the plastic clips. So the plastic under the 3 knobs has all broken away.

I think these could be just plastic washers. Not sure of the size as the old ones have literally disintegrated.

 

[mdog69]

The damaged devices are preset potentiometers aka preset variable resistors (hence the VR3, VR2 and VR1 labelling on the PCB).

Someone who has actually seen one of these things will be along shortly to help you, but in the meantime:

You may want to look at page 5 (6th page in the PDF) of https://wiki.console5.com/tw/images/8/87/Sega_SC-3000_Service_Manual.pdf

The minimalist one paragraph explanation of how the 9929 output is turned into RGB is on page 18 in the PDF (marked - 17 -)
The relevant circuit diagram is on page 6 in the PDF (marked - 5 - )

It looks as if VR1 seems to control a DC level on the R and B outputs (thus providing adjustment of the G signal, by adjusting R and B together)
It looks as if VR2 and VR3 are used to set the level of the individual R and B outputs.

VR2 and VR3 are 470ohm (hence the "471" marking = "47" plus one "0" = 470)
VR1 is 10k (will be marked "103" = 10 plus three zeros = 10000 = 10k)

If I were to replace the damaged devices, I'd set them to midway, display an image in black and white then adjust VR1 so that the image was not too green or too magenta (magneta=red+blue) and as close to white as possible.
Then adjust VR2 and VR3 to add/remove red and/or blue as required - find a picture showing how RGB mix using additive colour mixing, to guide your brain, then let your eyes give you the feedback for the adjustment. (This all assumes you aren't colour blind...)

I found the service manual by googling for "Yeno SC3000 service manual" then clicking on "images" - my intention was to find a circuit diagram and the PDF popped up.

 

[mutantcamel101]

Thank you for all that. Looking at variable resistors they all look different to the existing broken ones. Maybe I will need to desolder one to be able to get a better look at. I'm hoping that I can buy replacements. If anyone knows the actual ones I need please let me know. If not I can take a better photo.

 

[mdog69]

Thank you for all that. Looking at variable resistors they all look different to the existing broken ones. Maybe I will need to desolder one to be able to get a better look at. I'm hoping that I can buy replacements. If anyone knows the actual ones I need please let me know. If not I can take a better photo.

The only factors when replacing them is (1) do the pins match the holes on the PCB. (2) Are they small enough given the amount of space on the PCB.
I would also choose devices which are enclosed rather than "skeleton" ones - the type where the track and slider are exposed.

 

[mutantcamel101]

Thanks would these be possibly suitable? Not sure what the difference between 470K and 470R is though.

TRIMMER, 470K, Trimmers, Potentiometers & Variable Resistors | T7YB474MB40 | eBay UK

Product Range: T7 Series. Tolerance -: 20%. Temperature Coeff. -: 100ppm/�C. +: 100ppm/�C. Resistor Mounting: Through Hole. Resistance: 470kohm. 55�C to +125�C.

www.ebay.co.uk

Regarding the 10K resistor is there a particular type I would need?

 

[mdog69]

470k is 470,000 ohms
470R is 470 ohms - the one you want to replace VR2 and VR3

 

[mutantcamel101]

Thanks I found some on RS components that I can collect locally.

3329H-1-471LF | 470Ω, Through Hole Trimmer Potentiometer 0.5W Top Adjust Bourns, 3329 | RS

uk.rs-online.com

3339P-1-103LF | 10kΩ, Through Hole Trimmer Potentiometer 0.5W Top Adjust Bourns, 3339 | RS

uk.rs-online.com

 

[mutantcamel101]

Not sure if these will be ok or not. They have a lot of technical info I don't really understand.

 

[seat safety switch]

Those seem like they should work fine for this purpose. Definitely a different board than my Japanese SC-3000 has.

 

[mutantcamel101]

I'm trying to take my Yeno apart I think they might be some tabs or even the power switch holding the main board into place.

Can anyone help?

 

[seat safety switch]

The power switch on my non-Yeno SC-3000 was soldered in place and needed to be desoldered to pull the board out.