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MostroVeneno

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Hi my friends,

I recently got my first candy cab, a sega astro city, and i have been working on restore it, mostly aesthetically.
The thing is when powering the cab (as the title says) im not getting blue signal on the monitor.
Can anyone give some advice on how to proceed? can be the harness, a solder point in the chassis, a lose cable etc,
Can anyone point me some directions on what, how and where to try to test first to fix this issue?

20190625_231323.jpg


Thanks my friends in advance :)
 
I agree first start with the basics of adjustments. After that A missing colour not show on Mon will usually be one of these type of things:

- issue with the game board not outputting the colour
- issue with the wiring from the game board to the Mon chassis
- cold solder joints at the video input section of the Mon chassis
- video processing IC on the Mon chassis
- Colour drive transistor on the Mon neckboard
- bad trim pot
- cold solder joint on the CRT neck socket where connects to tube
- bad cathode in tube itself


Those are most likely but not complete list. All are fairly easy to test. If you have oscilloscope will drastically reduce your troubleshooting time for the blue signal. If not then start by breaking down to smaller sections (ie is it game board, is it wiring, is it Mon). If you see it's Mon then you break it down father, is it on tube or is it chassis issue (can ground blue cathode to check tube). From there just keep narrowing down etc. Video circuits are nice to test because there is literally 3 identical circuits and 2 of yours are working. Cab easy change parts and inputs/outputs around to verify issues and components.
 
@brad808 thanks mate!!
i will have this as guide to trying troubleshooting things, i will also try to get an oscilloscope if things get harder, thanks again very informative i appreciate this info. :thumbsup:
 
I had a "no blue" on the last Nanao I picked up. Not saying you have the same issue, but check the PCB that's attached to the back of the tube. If you see any solder joints that look questionable try reflowing them. That fixed it for me.
 
I had a "no blue" on the last Nanao I picked up. Not saying you have the same issue, but check the PCB that's attached to the back of the tube. If you see any solder joints that look questionable try reflowing them. That fixed it for me.
@Aurich i will have this in my mind, it´s good to know buddy!
 
The bias is so low for all of those channels, that I'd first kick up Blue bias and see if you can at least see it in the raster.
 
- issue with the game board not outputting the colour
- issue with the wiring from the game board to the Mon chassis
- cold solder joints at the video input section of the Mon chassis
- video processing IC on the Mon chassis
- Colour drive transistor on the Mon neckboard
- bad trim pot
- cold solder joint on the CRT neck socket where connects to tube
- bad cathode in tube itself
So far, this is the progress:

- issue with the game board not outputting the colour
- issue with the wiring from the game board to the Mon chassis following the blue cable from the harness to the chassis makes connectivity
- cold solder joints at the video input section of the Mon chassis
- video processing IC on the Mon chassis have to double check but at least the pins seems fine and pass continuity test
- Colour drive transistor on the Mon neckboard
- bad trim pot tested fine with multimeter
- cold solder joint on the CRT neck socket where connects to tube
- bad cathode in tube itself tested blue pin to ground and blue appeared for a sec.

So far i have spotted this issue:


Screenshot_20190626-205903_WhatsApp.jpg




Screenshot_20190626-205856_WhatsApp.jpg

First pin leg from bottom to top seems disconnected on purpose by design but second pin seems corroded and broken.

The datasheet for chip HA11423 says its a Color TV Deflection Signal Processor


Screenshot_20190626-205849_WhatsApp.jpg


Seems resistance soldered over patched trace.
 
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That ic is nothing to do with your colour display. That is sync and drive processing.


Do you know how to check transistors? Very common problem on all Mons is the colour drive transistors on neck board. See three mini transistors probably on heatsink? One red, one green, one blue. That is a good place to check since so common of a problem. If you don't know how to check transistor you can simply switch R or G with the B one. Then see if your problem moves to r or G. If it does then you know part is faulty.
 
Hi mate thank you for the response and feedback!
I´ll try that as soon as i get back from work and i´ll report back, sorry for the little knowledge from my side.
 
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Anyone knows whats a good replacement part for Colour drive transistor on the Mon neckboard, its a 2sc4001 transistor.
 
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Hey guys, I know it's typically not great form to bump a thread this old, but I too now have a Nanao MS-8 that won't display blue.

So far I've tested with a 19-in-1 jamma board and with a mister + j-pac setup and I get the same situation. I have tried adjusting the blue-gain on the monitor controls but it makes no difference. I have also tested continuity from the jamma harness to the the monitor chassis connector and RGBS are all good there.

I've read through this thread, but to be perfectly honest this is my first arcade cabinet and I'm a bit lost going beyond this for troubleshooting.
 
@bbickell

What about blue cut-off adjustments?

Have you wiggled the blue wire on the jamma harness to see if maybe it's not making proper contact with the PCB?

Follow that wire. Is it connected to the chassis?
 
Blue from the jamma tests good continuity into the chassis. Chassis plug tests good to the first small connector into the actual chassis pcb as well.

After that I'm a bit lost.

Is blue cut-off adjustment the same thing as the blue-bias in the Nanao manual here https://imgur.com/trjxrkX ?

Everything looks pretty decent with the wiring of this astro city. KC sent me some video of it before I received it and it looked good before it got on the truck, but now that I'm looking through some photos he sent me it actually looks like this might have started after his folks flipped it from vert to horiz if that rings any bells?
 
@bbickell I'd thought there were RGB cutoff pots on the neckboard of an MS8 but I may be misremembering.

Assuming you know basic CRT safety, unplug every connector on the chassis and plug it back in. Including removing the neck card and putting it back on. Because it's possible something rattled loose in shipping.

If that doesn't fix it, sounds like it's the seller/shipper's responsibility to step in.
 
Ok, I will do that. I've not ever removed a neck card or fussed with one yet. I did discharge a monitor for the first time a few days ago to take it out and I've got the remainder of the Astro City looking pretty great, I'm just high centered on this monitor issue.

Other than being very careful, taking your time and gently rocking the neck card off the connector, is there anything I should know?
 
@bbickell not really. It's pretty easy. If you've discharged a monitor you're capable of anything else here.

Something shaking loose in shipping is entirely possible. So I wouldn't lose hope or anything. You can also clean the connectors with electronic contact cleaner. Can buy it at your local auto parts store, comes in a spray can. Spray, tooth brush, let dry an hour or so, plug them all back up.
 
Stupid question, but well, I don't guess there are stupid questions about safety: I have the monitor sitting out on the floor on a piece of cardboard. No grounding wires are hooked to anything from the monitor cage to the cabinet. Does this alter my discharge protocol any?
 
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