I need advice: swapping CRT in an arcade cabinet. - Page 1
Forum section: electronics / repair

author: DC Jack
author_rank: Contributor
timestamp: June 08, 2025, 01:00:06 am
content: I am working on restoring an old school Golden Axe arcade machine and am having a hell of a time with CRTs and the chassis that drive them. I’m hoping some of you fine folks still remember something about them and might be able to clear some things up for me.When I got my hands on the arcade cabinet the original 19”/48cm CRT (Phillips) was cracked and the chassis (Wells Gardner k7000 series) that drove it had also failed. I managed to fix the chassis by replacing the flyback, replacing the linear power supply voltage regulator, and replacing the Horizontal Output Transistor. I also replaced every capacitor for good measure since the chassis is from the mid 80s and the bottom side had a lot of indication of running hot overheating. The bottom also needed a whole lot of lifted and torn trace repair and joint crack fixing. I hooked it up to a CRT that I salvaged from a commercial TV but I did not know at the time that not all CRTs are created equal at that time.The chassis seems designed to drive a yoke with Horizontal inductance of 1.5mH, and a Vertical 10.2mH (according to what I’ve been able to glean from other forums), give or take as with all electronics. Unfortunately I don’t have any inductance readings off the original yoke as I did not know that was important when I sent the original cracked tube to the dump, but the readings are available on other arcade forums. That said, the replacement tube has a Horizontal reading of 3.46mH and a Vertical reading of 50.7mH. Unfortunately these readings compared are well outside of the 10% wiggle room seen in most mass manufactured electronics. While the picture vertically is working well enough, the picture horizontally has serious problems. The picture is shifted about an inch (3-ish cm) to the right and squished on the right edge so that squares look like rectangles for the last inch of the picture. If the position of the picture is adjusted then the right side of the picture shifts left and right, and the farther it is moved away from the right edge the picture corrects itself and squishing is corrected. On the other hand the left side of the picture does not get any closer to the left edge of the tube and it simply collapses into the picture itself making a much brighter vertical line where “pixels” (for the lack of a better word) all merge together.I am confident there is nothing else wrong with the chassis and this is simply a compatibility issue with the yoke. My question for you all is, is there a way to adjust or modify the yoke to make it play nice with the chassis. Can I add some combination of resistor/cap in parallel to the windings so that it would drop the impedance? Is something like this even in the realm of reality?This question probably makes it clear that I know very little about analog electronics so I am looking for help.

author: m k
author_rank: Super Contributor
timestamp: June 09, 2025, 08:06:12 am
content: Usually swapping a CRT means more than a tube.Normally deflection is symmetrical, so center is zero deflection field.Since one side goes over there is enough voltage for that direction.Since other side can't reach the actual other side its deflection field of that moment is too weak.When you change H-Pos you should change DC level and timing of zero crossing of slow slope of deflection sawtooth wave.Since one side is not going further its side of deflection voltage can't go any higher and that side of the wave should have a flat top.Is the center of the picture close to center of the screen?

author: DC Jack
author_rank: Contributor
timestamp: June 10, 2025, 02:37:29 am
content: Yes, the picture is close to the enter of the screen. It's only off by 2 to 3 centimeters shifted right.Quote from: m k on June 09, 2025, 08:06:12 amThis I do not understand. I think I'm going to need to go to the library and hope they have some CRT technical books.

author: m k
author_rank: Super Contributor
timestamp: June 10, 2025, 09:11:17 am
content: Are old and new tubes meant for equal anode voltage, how much is it?High enough and the tube can emit x-rays.Ishttps://files.arcadeinfo.de/Monitore/Wells-Gardner%20K7000.pdfa correct manual?If so then have you tried HOR POS jumper in L position?Are colors correct?Cyan, magenta and yellow.Search 'RGB vs CMYK' and check manual page 7/23.If you disconnect the yoke you can check where the center of the screen is.How much it differs from estimated center of the picture when yoke is connected?Manual page 13/23 has HORIZONTAL OSCILLATOR AND OUTPUT.

author: DC Jack
author_rank: Contributor
timestamp: June 10, 2025, 04:52:35 pm
content: This is extremely helpful. I will look into all of this and report back.Thank you again.

author: CaptDon
author_rank: Super Contributor
timestamp: June 10, 2025, 06:06:09 pm
content: Trying to operate the CRT with the yoke disconnected is a dumb idea. The Yoke is indeed a critical part of the horizontal sweep and high voltage generation flyback circuit. With no deflection you MUST turn the brightness down or risk burning the phosphor where the pinpoint undeflected beam hits the screen. In a raster scan television the horizontal circuit operates as a tuned circuit usually with a damper diode which may be built into the horizontal output transistor. Throwing the old yoke away with the bad CRT was of course very short sighted!!! Modifying the incorrect yoke is a true crap shoot. And we still don't know if the yoke is the real reason for the offset.

author: m k
author_rank: Super Contributor
timestamp: June 10, 2025, 06:45:52 pm
content: Yes, my bad, do not operate the thing with yoke disconnected.It's only for a moment that you get the info.It's also better to do all testing with low brightness.When H-Pos is tuned to the left, is brightness of left edge of picture increasing?There is a blanking period.It's the time when beam is returning from one edge to the other and shouldn't be visible.If blanking is active the side can't collect brightness by more visible beam time over one vertical position.Yoke has a screw that tightens it to the neck.Have you tried loosening it, then moving the yoke a bit back and turning it horizontally?When you move the yoke, don't leave it hanging loose, put something in between and tighten it again, but not too tight.

author: eurgenca
author_rank: Regular Contributor
timestamp: June 11, 2025, 05:21:03 am
content: If I remember correctly arcade cabinet usually use 110 degree deflection angle while TV sets use 90 degree deflection angle, so you need to do some mods. I remember that hantarex chassis have some transformer adapter for different yoke.

author: jonpaul
author_rank: Super Contributor
timestamp: June 11, 2025, 05:50:33 am
content: beware implosion risque.Larger the CRT the more dangerous.j

author: eurgenca
author_rank: Regular Contributor
timestamp: June 11, 2025, 05:53:35 am
content: Like this.

author: DC Jack
author_rank: Contributor
timestamp: June 14, 2025, 12:03:49 am
content: That's an interesting device.

author: Paceguy
author_rank: Regular Contributor
timestamp: June 15, 2025, 11:10:47 am
content: In my early days of electronics, I worked on many TV's. One thing that I learned was that crt substitution was not that easy as just swapping crt's. In many cases, the exact replacement was needed. That's one of the reasons that there were companies that re-built crt's. Unless one is willing and has the expertise to re-design the horizonal, veritical and high voltage section, I doubt that using a different size, and deflection angle crt is possible.

author: m k
author_rank: Super Contributor
timestamp: June 15, 2025, 05:58:46 pm
content: Do you have a recollection of generally asymmetrical deflection coil sides?

author: DC Jack
author_rank: Contributor
timestamp: June 17, 2025, 01:47:35 am
content: I have a bit of an update. I don't know how, with all of my fixing and rebuilding of the board, but I completely missed the horizontal position jumper. I selected the left option and now the picture is centered, but not wide enough.Picture width on the k7000 is adjusted my changing out a capacitor. The original width cap value is 0.39uF. I played around with cap values all the way down to 0.10uF but the edges were severely compressed on both sides at that point and there was still a gap of about a centimeter between the picture and the edges.The best value seems to be 0.29uF. After that there is a point of diminishing returns. The strangest thing I've noticed while testing different values is that the right edge did not move when the capacitors were changed, only the left edge expanded and the picture needed to be centered. The problem became that at below 0.22uF the right edge started to bunch up into a single vertical line.MK, that manual is the correct one.In the mean time I've learned about parallel wound yokes, but I don't understand why that's a thing. More current capacity?

author: m k
author_rank: Super Contributor
timestamp: June 17, 2025, 11:20:52 am
content: Generally you have four adjustments, position, width, linearity and pincushion, all are possibly affecting others.Your machine has only first two.Your width is a coil, L1 size adjust, inside it is a hex hole ferrite core, manual page 4/23 has more.Don't break the core.Mentioned hexagonal adjustment tool is a plastic mold with hex tip.It must be magnetically inactive and mechanically soft, search TV alignment tool.You can test the size by putting a small metal screwdriver close to the coil's core, but don't be tempted, don't try adjusting it.With bad luck the core is stuck and your hard screwdriver tip breaks it, it's also possible that its position is secured with a tip of glue.