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Single dot on screen after chassis/tube transplant

Posted: December 23rd, 2020, 4:11 pm
by matt5cott
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As title, after a transplant of chassis & tube into a new cab I'm met with this single very bright dot in the screen centre (does appear to change colour when game has loaded)

Chassis/tube both working fine pre transplant.

Suggested fist things to check please other than wiring?

TIA 8-)

Re: Single dot on screen after chassis/tube transplant

Posted: December 23rd, 2020, 4:37 pm
by RandomRetro
Looks like you forgot to plug in the deflection yoke for horizontal and vertical, or something is up with the yoke.

And don’t leave it on long like that. It will burn that dot in fast.

Re: Single dot on screen after chassis/tube transplant

Posted: December 23rd, 2020, 4:54 pm
by matt5cott
RandomRetro wrote:
December 23rd, 2020, 4:37 pm
Looks like you forgot to plug in the deflection yoke for horizontal and vertical, or something is up with the yoke.

And don’t leave it on long like that. It will burn that dot in fast.
Many thanks 8-)

It's been on like this less than 20 seconds total as I did worry about it burning in due to the ridiculous brightness! So hopefully no damage done 8-)

Re: Single dot on screen after chassis/tube transplant

Posted: December 23rd, 2020, 8:29 pm
by radiantsvgun
Make sure the yoke wires are connected in the right positions and secured.

I had this same issue with my canary and the yoke wires were not making a good connection.

Re: Single dot on screen after chassis/tube transplant

Posted: January 4th, 2021, 9:26 pm
by matt5cott
Yeah this hadn't been wired correctly in a couple of places, I've worked from old picures (I normally colour mark the cables to connectors)

It looks wired up right now, but there's just a loud buzzing from behind the tube when I turn it on :oops: no picture at all.

Re: Single dot on screen after chassis/tube transplant

Posted: January 5th, 2021, 12:52 am
by RandomRetro
yoke is pressed up on tube, or wedge mounts, and neck board is plugged in and powering up? Any neck glow?

Re: Single dot on screen after chassis/tube transplant

Posted: January 5th, 2021, 8:33 am
by nem
Take some pics of the chassis showing what you have plugged in.

Don't turn it on. You shouldn't be hearing a loud buzz at any time.

Re: Single dot on screen after chassis/tube transplant

Posted: January 5th, 2021, 10:24 pm
by mikejmoffitt
Without deflection you might expect a hole to be burned within seconds.

Use an ohmeter and check that you get some resistance on both windings of the deflection yoke (with it powered off, disconnected from the chassis). This way you can check that your yoke is not somehow an open circuit.

Re: Single dot on screen after chassis/tube transplant

Posted: January 6th, 2021, 5:03 pm
by matt5cott
Thanks everyone for your feedback 8-)
RandomRetro wrote:
January 5th, 2021, 12:52 am
Any neck glow?
Currently no.
mikejmoffitt wrote:
January 5th, 2021, 10:24 pm
Without deflection you might expect a hole to be burned within seconds.

Use an ohmeter and check that you get some resistance on both windings of the deflection yoke (with it powered off, disconnected from the chassis). This way you can check that your yoke is not somehow an open circuit.
Noted, thanks :)
nem wrote:
January 5th, 2021, 8:33 am
Take some pics of the chassis showing what you have plugged in.
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Re: Single dot on screen after chassis/tube transplant

Posted: January 7th, 2021, 1:27 pm
by geotrig
Very hard to tell from the pics if anything is not connected , most looks to be from what i can see , cant see what is connected to the neckboard, only can see the ground ? also that wiring :eek: :wtf: seems like an awfull a lot of wiring in there overall though.

Re: Single dot on screen after chassis/tube transplant

Posted: January 7th, 2021, 1:50 pm
by PrincessPrinPrin
Yoke connector visible in the last pic (red/blue/yellow/green wires). Whether it is plugged all the way in or not remains to be seen. The header could have broken solder joints due to wiggling. Try the other header.

Re: Single dot on screen after chassis/tube transplant

Posted: January 7th, 2021, 2:47 pm
by nem
Unplugged yoke doesn't explain why's he's getting a loud buzz instead of a picture.

Is this is an earth ground wire?

canary_wire.jpg
canary_wire.jpg (81.65 KiB) Viewed 554 times

Re: Single dot on screen after chassis/tube transplant

Posted: January 7th, 2021, 3:22 pm
by matt5cott
Thanks again all for the responses 8-) 8-) 8-)
geotrig wrote:
January 7th, 2021, 1:27 pm
Very hard to tell from the pics if anything is not connected , most looks to be from what i can see , cant see what is connected to the neckboard, only can see the ground ? also that wiring :eek: :wtf: seems like an awfull a lot of wiring in there overall though.
Yes it's not pretty or colour co-ordinated wiring! The MS8 had less wiring, bloody TOEI has loads.

PrincessPrinPrin wrote:
January 7th, 2021, 1:50 pm
Yoke connector visible in the last pic (red/blue/yellow/green wires). Whether it is plugged all the way in or not remains to be seen. The header could have broken solder joints due to wiggling. Try the other header.
OK. Will stick that on my to try list.
nem wrote:
January 7th, 2021, 2:47 pm
Unplugged yoke doesn't explain why's he's getting a loud buzz instead of a picture.

Is this is an earth ground wire?

canary_wire.jpg
Yes, original cable was very short and used to ground directly to chassis, but nothing to ground it to since the swap so I extended it to a grounding point.

Re: Single dot on screen after chassis/tube transplant

Posted: January 12th, 2021, 12:39 am
by matt5cott
:palm: :wave:
OH HELLO WHAT DO WE HAVE HERE

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Must have been knocked during transplant, and for once it's not my soldering that gave way, someone else did the caps on this one years ago :lol:

I've not had chance to do anything with it yet as I spotted this last thing, it was one of those cases where if it was pushed into the board it looked fine.

Hopefully the time line is it didn't work as it was wired up wrong, but with the track just about making contact hence the single dot, but when it was wired up right this track was knocked out.

Re: Single dot on screen after chassis/tube transplant

Posted: January 12th, 2021, 9:58 am
by nem
Nice catch. Fingers crossed then.

Re: Single dot on screen after chassis/tube transplant

Posted: January 12th, 2021, 10:31 am
by ravepants
Fingers crossed on that mate.

Desolder the cap, epoxy the track back onto the board and wait for it to harden, then either repair the track with a jump wire or jump it to the next available component with some higher gauge wire and solder the cap back in. someone correct me if i'm wrong! but thats how i'd do it.

Re: Single dot on screen after chassis/tube transplant

Posted: January 12th, 2021, 1:31 pm
by PrincessPrinPrin
That's one of the two decoupling caps on the 200v supply voltage for the RGB amp transistors. Not related to the missing deflection.

Re: Single dot on screen after chassis/tube transplant

Posted: January 14th, 2021, 5:07 pm
by matt5cott
PrincessPrinPrin wrote:
January 12th, 2021, 1:31 pm
That's one of the two decoupling caps on the 200v supply voltage for the RGB amp transistors. Not related to the missing deflection.
OK thanks, deflection isn't the issue atm, doesn't even power on just buzzes!


Got some epoxy on the way so I can repair this properly :)

Oh and the chassis gets power via a 2 pin plug which I've cut off as per below, presumably I can just wire the remaining cable into the AC lines in the cab 8-)
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