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Author Topic: k7000 19" screwy color behavior  (Read 4543 times)

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snappleman

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k7000 19" screwy color behavior
« on: August 03, 2021, 04:36:48 am »
I got a broken/for parts k7000 chassis to mess around with and got it mostly rebuilt and working except this one issue:



When I got the board I noticed there had been no work done at it at all, it was all untouched. The flyback was cracked and a couple of the pots were broken off. I replaced the pots and fired it up, the red was all over the screen, focus and screen controls on flyback did nothing, brightness and contrast did nothing, red drive/cutoff took the red down some, but picture was still tinted red with retrace lines. I then tested Q201 (red transistor) and it was shorted, so I replaced the flyback, did a cap kit, replaced Q201 and reflowed the entire board.

Now everything works great except the red shows up like that pic, on one side of the screen and with retrace lines in it (no red anywhere else). When I short the Q201 heat sink to the chassis the screen goes full red so that should be fine? Every component on the red line is testing correctly, except R7. R8 and R9 are coming in at 8k rather than 33k as listed in the schematic but they're all the same and properly color coded so I assume they're fine. Tomorrow I'll swap out Q1, even though it tests fine in circuit I want to be thorough, and the drive/cutoff pots are also testing fine (but adjusting them does not affect that red blotch at all), but if swapping out Q1 doesn't fix it, does that mean IC1 could be shot?

I mean something clearly happened to this board for the pots to be broken, and for Q201 to be fried, and I'm not experienced enough to be able to tell if it's a neckboard or mainboard problem, but if everything going to IC1 looks ok, and everything on the way out from IC1 to the CRT socket looks ok, then should I order a replacement IC1 and swap it out? Or can the drive/cutoff pots be faulty even if they test well in circuit?
« Last Edit: August 03, 2021, 04:43:18 am by snappleman »

snappleman

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Re: k7000 19" screwy color behavior
« Reply #1 on: August 04, 2021, 01:20:44 am »
So today I went in and just shotgunned the entire red signal path, every single component replaced, the transistors, capacitors, resistors, diode and pots since I had everything on hand.

The red blotch is gone, picture looks great, but still no red at all. The screen still goes red when I short the transistor, but otherwise there is no red in the picture. With the pots doing nothing I'm thinking the signal just doesn't get past the IC. The traces/continuity past the IC all check out so at this point I think it's definitely a faulty chip. Gonna order a replacement and see if that does it.

bobbyb13

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Re: k7000 19" screwy color behavior
« Reply #2 on: August 04, 2021, 02:44:28 am »
I don't know enough about this to have any clue what is going on but I am damn curious to know what it is!
Relax, all right? My old man is a television repairman, he's got this ultimate set of tools! I can fix it.

lilshawn

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Re: k7000 19" screwy color behavior
« Reply #3 on: August 04, 2021, 12:38:54 pm »
more often than not, a missing color when the neckboard is not at fault is either the tube has a bad gun (but you've tested this already.) or the amplifier IC gone bad. in the k7000 this is the UPC1397C . good luck on your search, it can be very hard to come by.

i'd double check your board/game/computercable is operating properly by feeding, say the green signal, into the red on either side of the IC. if you can confirm video signal is getting in by swapping red to another color channel, the IC is bad.

snappleman

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Re: k7000 19" screwy color behavior
« Reply #4 on: August 04, 2021, 07:54:52 pm »
Yeah I made sure to swap around the signals and all that to verify. Getting a upc1397c was really easy though, arcadepartsandrepair has them for $10, as does arcadecup via ebay. Also the tube is a brand new old stock TV I just got that's listed as a compatible replacement for a K7000 (which is why I got the board to try that out), so that should be fine for a while.

nfabozi

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Re: k7000 19" screwy color behavior
« Reply #5 on: August 09, 2021, 06:27:37 pm »
Not sure if the issue is similar but I wanted to mention it. I have a game with blotchy color that looks like this:



I found out that if I move these magnetic beam adjusters, I am point it one with my yellow flat head screw driver (don't know the terminology), the image started to clear up


Here is after


I still have some adjusting to do but wanted to mention my finding if at all related to your issue. I could not see all of your picture very well. The lines in your image are probably from the screen adjustment on the flyback being turned up too high.

snappleman

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Re: k7000 19" screwy color behavior
« Reply #6 on: August 12, 2021, 02:38:15 pm »
The lines in your image are probably from the screen adjustment on the flyback being turned up too high.

The lines only appeared on the red signal on that one part of the screen, that was due to open resistors before the red chroma transistor. I replaced the damaged video IC and everything is perfect and working well now:



Hard to take photos of CRTs but the image on this one is spot on, no color issues, even the convergence is mostly on point all around the screen.

I'm not sure exactly how this happened to the board in the first place (among the other issues it had since it was broken), but this seems like it started from the IC, taking out the resistors and the transistor? Whatever the case it's working well now.

The only remaining question I have is if can I safely move that large cement resistor that's by the filter cap and affix it to the heatsink just like the other resistor? I want to fit this board into a TV and I don't like that resistor being up that close to the tube, if I use some heavy gauge heat resistant wire maybe? If that's not a good idea maybe slapping some kapton tape on the tube around where the resistor is?

lilshawn

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Re: k7000 19" screwy color behavior
« Reply #7 on: August 13, 2021, 03:13:14 pm »
glad you are sorted out.  :cheers:

any number of things can cause it. static can build up and discharge through the IC killing a color. a failed driver tranny can short in such a way as the 80 some odd volt color drive voltage gets back-fed into the IC blowing the channel. it happens. make sure all the grounds are hooked up and it's fine really.

and that resistor is fine. it doesn't get hot enough to do anything to the tube anyways. i suppose it might be keeping the cap next to it slightly hotter than it would be so otherwise... the amount of failures on the k7000 i've seen in the last 14 some odd years... related to something like that, is currently zero.

old caps, dead STK's and fried transistors are about the only things I've ever had really consistently happen.

snappleman

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Re: k7000 19" screwy color behavior
« Reply #8 on: August 13, 2021, 04:22:46 pm »
 :cheers: It feels good to finally actually fix something after a lifetime of destroying everything I touch B)

MKFan4Life

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Re: k7000 19" screwy color behavior
« Reply #9 on: August 18, 2021, 04:19:34 am »
Just happened across your post. Noticed you had weird values for R7, R8, and R9 (according to the parts list or schematic). I have been double-checking everything on my 25" K7000 while waiting on a replacement for C44 I found shorted.

Well, my R7, R8, & R9 are reading like yours. I thought they were bad parts, although I figured resistance would go up, not down. Seems that the parts list on the two K7000 PDF's I have looked at are either wrong, or I am missing something.

The paragraph above the parts lists say the parts are the same across all K7000's unless otherwise noted. Then afterwards I do see smaller sections listing certain specific parts likes caps & resistors for the P447 (19" as I understand it) and the 25" models, which I think are usually P538, although my 1990 chassis has no designation like this, but it has a long number on the underside including 5357P-007, and a sticker designating it's a 7197 on top of the HOT heatsink.

I had replaced a VR, STR 30130 last year on this chassis when my MK1 cab. It ran fine except it needed new caps, as the last kit I did was from Bob Roberts about 10 years ago. Well, I was playing it and adjusting the flyback one night, and the entire cab shut off. Blew the main 3 Amp fuse in the cabinet. I disconnected the monitor and the cab ran fine blind after replacing the fuse. Reconnected the monitor and realized the 2 Amp chassis fuse had bit the dust also. Replaced it, and it immediately blew again, but I cut the cab off fast enough to save the main cabinet fuse.

After taking the chassis out to examine it, I ended up replacing the HOT which was shorted, doing a cap kit from Arcade Parts & Repair, and then I found the STR 30130 I had installed last year was shorted, too. Luckily I had bought several VRs last year, so no problem. I was about ready to install a fresh VR (removed it from circuit, just like HOT, & they both still tested shorted) when I decided to start checking for shorts/bad parts and found that cap C44 shorted.

While awaiting that cap, I found those resistors way out of spec apparently. I think, as you do, they can't all 3 be low on resistance to almost the exact Ohm value. Did you ever find out why there was that difference in the three resistor values in the parts list/schematic you had?

(Sorry so long-winded.)
 :-\




snappleman

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Re: k7000 19" screwy color behavior
« Reply #10 on: August 19, 2021, 12:34:32 am »
I have no clue why they're not to spec but yeah they're all good and all factory so I ended up leaving them in. I've been researching a bit about K7000s and it seems pretty common to have factory mods or little differences here and there. If they had been somewhere "important" like the power supply or around the HOT I'd have changed them to match the schematic but they seem to be pretty isolated from any forms of danger.

On that C44 though, if you're not sure the flyback is good it might be smart to change that out as well.

MKFan4Life

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Re: k7000 19" screwy color behavior
« Reply #11 on: August 19, 2021, 01:59:51 am »
Ordered 2 polys with identical ratings for the C44 cap. The flyback was installed new a couple of years back when I stored the game here at home and was trying to figure out why the chassis went down (which ended up being the voltage regulator I replaced a year ago when I got the game out of storage to play some more).

I installed the new flyback since it was original to the chassis, and the old one had visible cracks. I hope it was not a dud flyback and caused all the stuff going on now. I heard there were some duds Bob Roberts sold in the past, and this came from him before he took that last break. I haven't heard anything about him in forever. Hope his health has improved.

 :D

MKFan4Life

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Re: k7000 19" screwy color behavior
« Reply #12 on: August 19, 2021, 10:27:17 pm »
I have no clue why they're not to spec but yeah they're all good and all factory so I ended up leaving them in.

Was curious and desoldered R7, R8, & R9 on my K7197. They all tested almost exactly 33K out of circuit. In circuit, they plop all the way down to about 7.9K. I also checked the color bands, and indeed, they are all 3 marked as 33K resistors. I don't look at bands much at almost 50 years old. I have a lot of trouble telling violet from gray or blue and sometimes think orange looks red. A good magnifying glass helps though.

I also tested R25, R26, & R27 which all tested differently in circuit than they were supposed to be valued at. Just like before, they all tested almost spot on when out of circuit when compared to the data from the WG specs. The color bands all denoted exactly the values the WG data lists.

Moral of the story: believe it when someone says parts test differently in circuit. Funny thing I noticed also, yesterday, I recorded the values of R25, R26, & R27 in circuit. Today, after pulling all 3 to verify their values, I put them back in, and all 3 gave totally different values than yesterday in circuit. At first, I was like, guess they haven't cooled down yet and the value is fluctuating. Then I waited about 15 minutes, and they never wavered from the new values.

The only thing I can think of is yesterday I had left the linearity coil out to test it, and left R98 & R99 each with a leg lifted to check their true value when I initially tested R25, R26, & R27. Those components altered the readings of the other 3 resistors in circuit I figure. I should know that. I studied several electronic courses working on a degree within the past couple of years, but calculating circuits was near the beginning of my courses, lol. Very rusty.

snappleman

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Re: k7000 19" screwy color behavior
« Reply #13 on: August 19, 2021, 11:41:09 pm »
Thanks for doing the legwork, I feel better knowing that. But now I'm thinking I should be a bit more methodical about shotgunning parts that are out of spec, and given that I'm just an amateur at this I'll learn any lesson that comes my way.

snappleman

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Re: k7000 19" screwy color behavior
« Reply #14 on: August 20, 2021, 10:28:27 pm »
Now that this chassis is mostly working (need to get the degaussing circuit fixed) I swapped on the matching k7000 yoke and it got the geometry even straighter and the convergence is still super nice. The next step is a bit tricky because having the chassis, isolation transformer, scart2arc and the switching PSU for that all in the TV case gets things very uncomfortably hot, and there's barely any room. So now after 20-some years in this hobby it's finally time I built my own Crapmame TV enclusure!

This is actually a big deal for me because my wife (girlfriend at the time) told me it was inevitable I'd build a Crapmame of some kind. It's taken 20 years but now it's time to make that a reality! 8) 8)

I figure I'll use some plywood to build a super bootleg box that houses everything and has a couple nice speakers in it, along with a couple 120mm PC fans on either side acting as intake and exhaust to keep things cool. I've built my own racks for studio outboard gear and they each weigh a solid 400+lbs each all loaded up and are still sturdy and standing after all these years, so I figure a CRT isn't gonna be too hard...

MKFan4Life

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Re: k7000 19" screwy color behavior
« Reply #15 on: August 21, 2021, 01:42:13 am »
I'm gonna go crazy. This is not the first time I've typed in a long reply and the board auto-logged me out, tossing the message content I had typed. Does anyone here know the length of time it takes to be logged out? I forgot to copy and paste my message into notepad, as I usually do in just this case. Sometimes hitting back on the browser restores the text, but not always. ARGH!

In a nutshell, build a MAME cabinet! I did it, loved it, and have tons of fun with mine!!!

 :-\

PL1

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Re: k7000 19" screwy color behavior
« Reply #16 on: August 21, 2021, 03:21:24 am »
Does anyone here know the length of time it takes to be logged out?
The default setting is 60 minutes.

On the login screen, you can either change "Minutes to stay logged in:" to a larger number than 60 or click on the "Always stay logged in:" checkbox.


Scott

snappleman

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Re: k7000 19" screwy color behavior
« Reply #17 on: August 21, 2021, 03:42:29 pm »

In a nutshell, build a MAME cabinet! I did it, loved it, and have tons of fun with mine!!!

 :-\

I'm in NYC so space for multiple cabs is at a high premium, I already have a vertical cab for shooters (that's currently on life support due to a shorted yoke damaging the chassis), so the best I can do is a TV to run mame and all my consoles, and this TV I'm using is not RGB moddable, but it's aparently perfect donor tube for a K7000 so I figured I'd give it a shot.

MKFan4Life

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Re: k7000 19" screwy color behavior
« Reply #18 on: August 23, 2021, 02:53:34 am »

The default setting is 60 minutes.

On the login screen, you can either change "Minutes to stay logged in:" to a larger number than 60 or click on the "Always stay logged in:" checkbox.


Scott

Thanks so much! This has happened to me on other forums, too, not only because I need to shorten my replies, but because I am doing multiple things at once often, and sometimes step away near the end of a reply and come back to finish the post. Usually, if I have a long reply, I just copy and paste it into notepad, not only in case the board somehow tosses the reply, but you might lose power at home, or your laptop dies.
Appreciate it man!
 :applaud:

MKFan4Life

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Re: k7000 19" screwy color behavior
« Reply #19 on: August 23, 2021, 03:45:21 am »

I'm in NYC so space for multiple cabs is at a high premium, I already have a vertical cab for shooters (that's currently on life support due to a shorted yoke damaging the chassis), so the best I can do is a TV to run mame and all my consoles, and this TV I'm using is not RGB moddable, but it's aparently perfect donor tube for a K7000 so I figured I'd give it a shot.

I see your problem living in NY. You have to make adjustments to be in this hobby at all with limited space.

Make sure you don't toss that tv tube, since it could be used for several monitor chassis models. If you don't have to buy an entire monitor, or ship more than a chassis, you have a problem licked already. I'd personally stick with an arcade monitor for nostalgia/authenticity reasons, but you have to do what works for you in your situation.

I got lucky with those capacitors I ordered to replace the shorted C44 from my K7000, as they arrived super-fast on Saturday. You know I said I had capped the monitor with a kit from Arcade Parts & Repair, replaced the shorted HOT & shorted voltage regulator. Then I installed the new C44 after having a day or so to go over the entire chassis, reflowing, cleaning flux, and testing everything I could think of, including diodes, resistors, coils, etc. I felt really good about the work I had done. The HOT and VR and the new cap all tested fine back in the board.

Well, while I had been waiting on the cap (& a new tube of heatsink compound), I examined a different K7000 chassis I had stored away about 8-10 years ago, because it really could use a cap kit, and I preferred the original from my MK1 which has adjustments on a remote board. Everything on it looked ok (except aging caps), so I installed it into the MK1 cab to verify it still worked in case I needed it. It worked just fine. That confirmed everything in the cabinet was working well, and I played it for an hour, adjusting it to the tube.

Then tonight, I put the original chassis I just recapped & did the repair work on back in and fired it up in the dark so I could see flashes of disaster. The main 2A SB chassis fuse immediately bit the dust once again. The cabinet fuse did not blow as it had the first time this chassis went out recently and the game was playing blind again.

I was able to test the HOT, VR, & C44 with the chassis installed, and the HOT & VR tested shorted, but C44 was fine. Now I need to pull it and double-check all my work... no that's triple-check, as I double-checked everything before. But I have missed something. I'm thinking it's that flyback. It has seen only a year of occasional play from time to time since it was in operation, but it was a few years back that I bought it from Bob Roberts. Also, I was adjusting either the Screen or Focus pot when the chassis took out both it's fuse and the cab's main fuse that night.

I'm going to start a thread about the chassis and see if I can get some advice. Thinking heavily about swapping the known good flyback from that other K7000 just to see if that is the culprit before ordering another.
 :o