Sharp Image SI-134 / KTM-F 33 Vertical Collapse++

Shoot you're fast I thought of something after I posted this if the voltage going into the flyback is wrong say 1/3 of what it should be then the output at the secondary is going to be one third lower as well so I was going to recommend to check the input voltage going to the flyback before you order a flyback I'm sorry
 
You can check the voltage at the cathode of D903. It should be B+ish voltage (130ish or so?). If it's not around that, and it's 30% (39ish volts or so) then the flyback is probably good. It's chassis ground again so same place as before. Leave your red lead on it (use a clip), so you can watch it as you turn the monitor on real fast then turn it off again.



At this point, however, I feel we're kind of throwing things at it instead of having the exact method and diagnosing the exact part to fix it. I'm just posting on what I would do in my troubleshooting practices and what the most likely causes are. I feel bad if you have already bought the flyback and it doesn't resolve your issue.

So, I can do a few things going forward:
  • I am interested in continuing helping you with this, however, we may approach, if we haven't already, a maximum cost for you to repair it, without just buying another chassis to fix the monitor. However, it's real tough to not see the chassis in front of me, take measurements immediately on components, and try different parts to see what happens. (I'm a parts changer and proud of it!)
  • I can offer, and ask the repair tech community here in this thread, if they fix these chassis' and if they want to take a stab at repairing it (I believe for sure Chad @arcadecup could fix this), but not sure how many others will want to take it on. The reason is it may not be economical to fix with how much time it will take, and the same reason happening here, lack of experience with brand that is a tougher chassis to repair.
  • I bought a brand new flyback that I was trying to fix a KTM-F 25in and have hit a brick wall with it also. The flyback should be good (I haven't even powered it up, the chassis has an issue with the VR) I'd sell it to you for half price $20 + shipping. It's the same exact flyback that you have there a KFS-61088. If you have not ordered the flyback this can be an option, but if you have, I apologize.

I just tried to get the thread back on topic so I thought hey maybe this is an easy one. LOL I just wanted to warn you this may be a slow-going process going forward.



So I would do the following. Look at the schematic and check all the components connected to R901. That would start with D901, C901, L901, C902, R906, C903, and continuing on and up through L602 until you hit T601. This means testing every component (out of circuit if necessary), checking for solder bridges/blobs, continuity to the next component in circuit, and anything else that looked out of the ordinary. And I would also just replace the flyback just to see if that resolves the issue. Because there is a cost associated with that, I would check the circuit components first.

You can use this info as a guide to testing things in circuit:
  • Resistors do not short, they go out of tolerance on the high side or go open. (1kohm turns into a higher resistance, 2kohm, 3.43kohm etc). This one getting that hot, there is something on this circuit that is connected directly to ground that is shorted, most likely. You find the bad component, R901 will probably be happy once again.
  • Diodes short circuit, so it will read shorted if bad. This does not mean they will not read wonky in circuit, but you can lift one end and test it if it is shorted.
  • Inductors are just wire, so they should read almost shorted or very low resistance in circuit. They go bad when they break, and they go open or a higher impedance.
  • And the caps, you can test with an ESR meter. I would honestly just check for shorts, or bulging (even if you just replaced them), along with solder bridges and blobs.
-Pat
 
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D'oh! Well, I appreciate the help and the offer. Already had the flyback in cart, debating on buying it. When you said it was probably the flyback, I just pulled the trigger. Was already on that path, so no worries.

I guess my limiting cost factor is about $250, three tanks of gas and 3 days on the road. There is a guy selling the exact tube and chassis I have, for that much, in Atlanta while I'm in Minneapolis :) Other than that, I got the monitor for free (I did have to drive to Iowa, and the guy assured me it was "working, but had vertical collapse,"), so if I get it running, it's all good. I'm willing to put in the effort if someone is willing to help with information I'm lacking. Sending it off to be repaired is going to be difficult. I did contact a few techs, but they all said they don't have a compatible tube.

Anyhow, I'll check the incoming voltage next, and individual parts leading from R901 next. Will report back with findings!
 
Sounds good let's continue! I know you said you already checked some of those parts but this is kind of how I get down to what to look for and what the possibility could be
 
Look at the schematic and check all the components connected to R901. That would start with D901, C901, L901, C902, R906, C903, and continuing on and up through L602 until you hit T601. This means testing every component (out of circuit if necessary)
Testing each component out of circuit.

D901: good
L901: good
C902: good
R906: Same issue as R903. Schematic calls for 2W 15ohm. Actual resistor is 2W 2.2ohm. It does read good, but what do I do here? R903 is 1.5 ohm on the schematic, but had a 15 in it. Changing it to 1.5 was the last thing I did before R901 started burning up. So which to emulate? What's there, or what the schematic says to use?
C903: good

Continuing to test.
 

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Also, I cant find D410. Is it this guy? This diode is unlabled on both sides.
 

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Also, also D903 is a jumper. No diode installed there. Right next to the no cap C909. It read 120v DC for the 2 or 3 sec it was active.
 

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Here is a copy to the manual I am using. https://archive.org/details/kortek-ktm-f-vision-manual/page/n21/mode/2up

Some manufacturers (like this one) use pretty much the same schematic/boardset for a smaller monitor, and change a few components for a larger monitor. This one is a 10in, 14in, 20in, 14in EGA, 15/17in, 25in, 26in EGA, 29in EGA, and finally 29in and 33in. So on page 22, it is showing the parts change for the 33in version of the monitor. As I said before, R903 on the 33in version is 15ohm 2 watt. However they did make a change to R906, it is 2.2ohm 2watt. So, 2.2ohm for r906 is correct. Use what has been described that has been changed for your version.

D903 is directly hooked up to pin 8 of the flyback and should be somewhere around 120v apparently, and 133ish (on my 25in I >>think<< it's supposed to be 133. So 120 may be fine.)

At this point since you already bought the flyback, and you're getting 3.69 volts off of cathode of d901, it's pointing to the flyback still. The flyback is a transformer and has secondary windings, which should be providing 12v off of the D901 measurement. It's not, and it's getting also an appropriate voltage on the input side, so that secondary winding, I believe, there is an issue with it.

I would say replace the flyback and see what happens.
 
Ah dagnabbit. Wish I had found that manual before I started this. I wonder if changing the R903 caused the damage to the flyback. Aw well, live and learn. Will check back in when the flyback is installed. Fingers crossed.
 
I would say replace the flyback and see what happens.

Dun dun duuuuuuuuun... didn't work. Hah!

New flyback installed, had to move some components to the under side of the chassis (as was mentioned in instructions), double checked my soldering and wire placement.

Popped it back on the tube, fired it up, 3 seconds then smoke. Same resistor as before.
 
Welcome to the Kortek pain, if you haven't felt it already.

At this point, can you take a clear HI RES picture of the bottom of the chassis and a clear hi-res picture of the front as well, so we/I can take a look and see if we see anything unusual.
 
Okay, I'm going to ask you to do a couple things, this is EXACTLY what I would do to check the joints.

Can you use the highest concentrate of rubbing alcohol or denatured alcohol you have (at least 90% but preferably 99% alcohol) with a tooth brush and remove all the flux over the lower half of the board, by the flyback. If you need to use a brass wire brush to get the stickiness off, that's ok. Try to make the bottom of it look brand new. After you do that, can you take another maybe clearer, hi-res pick of this "half" of the circuit board. Try to get T601 in the pic, and all of R906 (to the right side) and all the way down.

I am going to look at solder connections, etc and see what's going on. There are some questionable parts but I can't see them directly.

This is taken from arcadepartsandrepair tech section. (TY Peter!!)

Sharp-Image-KTMF-Monitor-Chassis-Bottom-scaled.jpg


Your lower half should look like this when you're done. And we can also use this to figure out what should connect to what. After you do that, I'll take a look thoroughly (anyone else can too!!) and see if we can find anything.

Honestly, this is what all the repair techs have to do sometimes to figure this out. Which sucks! But, it is what it is. :) And these chassis, in my experience, have you doing all of this more often.

-Pat
 
What resistance to ground do you measure on jumper J9 (or J8)?
An unstable number, right now. I assume there is still alcohol flashing off in places. What is the expected value?

Edit: huh, it never settles, even when dry. 3-5Kohms... ish. Either it starts low and rises to about 6.7K, or stars very high and drops to 7k.
 
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Problem areas:

problem areas resized.jpg

#1: Looks like a cold solder joint on the "right" side of C606. Refresh and reflow solder there, remove old and place new.
#2: These chassis have un"protected" traces in between capacitors as you see here. It looks like the bottom joint of C610 may be touching the trace running between the cap. Make sure there is no continuity from either leg of the cap to that middle piece.
#3: R901 has gotten hot and burned a little of the trace going from pin 7 on the flyback. Check resistance between the two points there just to make sure it's a complete short (should be less than an ohm, very close to zero. If it is not, clean off the soot, remove a little of the trace, and blob solder from that leg of R901 to the trace just to ensure it's getting a good connection. (may not be your problem, but could be in the future.)
#4: It looks like the right leg of C702 is touching the left joint of the jumper MKL was talking about, J8. Bend back and make sure there is no continuity there.
#5: Not sure what this component is, however the top 2 legs on the left look like bad solder joints. Refresh and reflow solder there, remove old and place new.
#6: (Just below D605) Oh that's T601. I don't think the 3rd leg from the left should be soldered to the leg to the right of it, but it is possible. Did you do that, or did it come like that?
Lower right hand side (forgot to number), it looks like that is R904, is it supposed to be on the bottom? And it looks like cold solder joints there as well. I'd put it on top if you could, or at least refresh the solder joints.

MKL is an excellent troubleshooter, try to answer his questions also with as much vigor as you've been answering mine. :)
 
check if any of the caps haave a short to ground on the positive side of the cap

Ya, I think that's what MKL is thinking also possibly. Something is shorting to ground on the circuit where R901 is. We just need to find it.

Oh and don't use steel wool. It leaves little pieces of itself everywhere which would be real bad. You cleaned it up good enough so we can see it now.
 
sounds like he is having the same issue i am with a kortek ktx-26, i still havent figured out whats causing the short to ground, i am either going to send it to someone or just start desoldering one leg of every component until its gone
 
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