Instant blown fuse with K7000

Kopey

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Okay, so I bought this World Rally which was playing blind. I recapped the chassis and neck board and replaced the flyback and HOT as well. I had noticed that the flyback had a small crack in the old one so I decided to replace it. When changing the flyback I noticed the chassis fuse was blown. I assumed that it got blown because the flyback might have been bad. I also put in a new power supply. Anyways, I turned it on and it blew the fuse instantly. After reading through the forum and some online links, it appears that I need to check a bunch of the following:

1) Check for short on C38.
2) Ohm out HOT (centre and third pin. If near 0 then it's shorted)
3) Check large ceramic resister parallel to VR.
4) Check C55, C56, C57
5) Check R84, R85, R86
6) Check C36, C38
7) Check diodes 19-24
8) Check D18.

I'm new to this stuff so just to make sure I understand this correctly, I need to desolder these capacitors, resistors and diodes to test them properly correct? I should mention that I don't have an in-circuit ESR reader, just a regular multimeter. Could it just be that my voltage regulator got fried prior to when I bought the game? Should I pull and test that first before anything else? Any other suggestions would be appreciated. Thanks.

Robert
 
I'd ohm-out the voltage regulator to be sure it's OK.
Also the input diodes/bridge need testing if the input fuse opens immediately.
I'd test the former out-of-circuit and the latter in-circuit. YMMV

I also like to ohm-out B+ to see there is no short (i.e. bad cap).
 
the diodes have to be tested out of circuit. if I'm not mistaken you'll read a junction drop both ways with them in circuit.

you test the HOT on a K7000 by black probe to frame ground and red probe to middle pin. if you get a 0.00 (shorted) reading on the meter in diode test, the HOT is blown; if it reads as open in diode test or high resistance in ohms, then it's good. this is done with the power off.

I've seen some pretty garbage flybacks on these but never seen a blown fuse caused by it. there's a whole network of resistors that carry power, if certain ones have severed solder pads (and thus no connection) it can cause the fuse to blow. shorted diodes could definitely do it, but the only way to really kill those is by plugging the monitor into a non-isolated power source. the last common way to blow the fuse is through the degauss coil that mounts to the tube; if there's a cut in the insulator to the coil and the exposed part touches the metal frame, it can blow the fuse, as it's operated by the same AC that powers the monitor itself.
 
The last K7000 I repaired, has this very issue. Original flyback developed cracks, and was blowing the chassis fuse. Check either C36 or C38(can't remember without looking), but one of those two had a leg that dissentigrated, and thus not working. I did the other usual checks, all other parts tested fine on it.

End of the day, it was that cap and flyback causing the fuse to blow. Of course, did a full cap kit(note C36 & C38 do not come in capkits), and re flowed solder all over the chassis, even after testing point to point for continuity. Mine was fairly obvious, once I looked in that area, hoping yours will be just as easy :)
 
The last K7000 I repaired, has this very issue. Original flyback developed cracks, and was blowing the chassis fuse. Check either C36 or C38(can't remember without looking), but one of those two had a leg that dissentigrated, and thus not working. I did the other usual checks, all other parts tested fine on it.

End of the day, it was that cap and flyback causing the fuse to blow. Of course, did a full cap kit(note C36 & C38 do not come in capkits), and re flowed solder all over the chassis, even after testing point to point for continuity. Mine was fairly obvious, once I looked in that area, hoping yours will be just as easy :)

both of those are valuable. they're both in the horizontal deflection circuit after all. could be either. I encourage replacements of R101 and C38 with all cap jobs, along with the patented Buffett "good reflow".
 
I'd ohm-out the voltage regulator to be sure it's OK.
Also the input diodes/bridge need testing if the input fuse opens immediately.
I'd test the former out-of-circuit and the latter in-circuit. YMMV

I also like to ohm-out B+ to see there is no short (i.e. bad cap).

Thanks. I will add those to my things to do list. : )

Robert
 
the diodes have to be tested out of circuit. if I'm not mistaken you'll read a junction drop both ways with them in circuit.

you test the HOT on a K7000 by black probe to frame ground and red probe to middle pin. if you get a 0.00 (shorted) reading on the meter in diode test, the HOT is blown; if it reads as open in diode test or high resistance in ohms, then it's good. this is done with the power off.

I've seen some pretty garbage flybacks on these but never seen a blown fuse caused by it. there's a whole network of resistors that carry power, if certain ones have severed solder pads (and thus no connection) it can cause the fuse to blow. shorted diodes could definitely do it, but the only way to really kill those is by plugging the monitor into a non-isolated power source. the last common way to blow the fuse is through the degauss coil that mounts to the tube; if there's a cut in the insulator to the coil and the exposed part touches the metal frame, it can blow the fuse, as it's operated by the same AC that powers the monitor itself.

Thanks for the reply. I took some more readings and will be posting my results shortly. I will take a closer look at the resistors and report back.

Robert
 
The last K7000 I repaired, has this very issue. Original flyback developed cracks, and was blowing the chassis fuse. Check either C36 or C38(can't remember without looking), but one of those two had a leg that dissentigrated, and thus not working. I did the other usual checks, all other parts tested fine on it.

End of the day, it was that cap and flyback causing the fuse to blow. Of course, did a full cap kit(note C36 & C38 do not come in capkits), and re flowed solder all over the chassis, even after testing point to point for continuity. Mine was fairly obvious, once I looked in that area, hoping yours will be just as easy :)

I pulled C36, C37, C38 & C69 and took some readings. I will post them shortly. Thanks for the help!

Robert
 
both of those are valuable. they're both in the horizontal deflection circuit after all. could be either. I encourage replacements of R101 and C38 with all cap jobs, along with the patented Buffett "good reflow".

Thanks. I pulled the C38 and will post my readings shortly. I haven't checked out the R101 yet so I will take a look at that as well. Thanks for the help, it's very much appreciated.

Robert
 
Okay, I took readings from the HOT and voltage regulator. I also pulled C36, C37, C38 and C69. Here are my readings:

HOT = 1.58 kohms (ohm setting) - Middle pin
HOT = 1.54 (Diode setting) - Middle pin

Voltage Regulator (STR 30130) - Ohm setting
Pin 1 = 1.5
Pin 2 = 14.55
Pin 3 = OL
Pin 4 = OL
Pin 5 = OL

Voltage Regulator (STR 30130) - Diode Mode
Pin 1 = 0
Pin 2 = 1.65
Pin 3 = 1.54
Pin 4 = 1.54
Pin 5 = OL
Sorry, I wasn't sure whether I was supposed to be on the ohm setting or diode setting so I took readings in both.

C36 = 3.19
C37 = OL (Showed 0 for about 30 seconds and then OL came on the screen)
C38 = OL (Showed 0 for about 30 seconds and then OL came on the screen)
C69 = 11.52

I also checked for continuity while I had them pulled from the board and C37 & C38 both had continuity. Capacitors are not supposed to have continuity if they are functioning properly correct? So does that mean C37 & C38 are toast and could be the cause of my problems?

I think that's about it for me tonight. Time to get some sleep and await your feedback regarding my readings. Thanks again for all the help everyone!

Robert
 
I don't have a cap tester, but I think with a meter on ohms they should read open if good. if you have continuity that implies it's shorted. as noted, C38 is the width cap, it directly ties into the horizontal deflection (and thus high voltage) portion of the monitor. that'll pop some fuses then.

you won't find that on a Randy Fromm flowchart!

I know there's that test for the voltage regulator, but I think you need to sort out your poly cap issues first. if you power the monitor up and it goes into shutdown, then you can suspect the voltage regulator is toast after confirming with a B+ test.
 
I have the exact same problem (u may have seen my threads on it).....no explanation yet as to why the fuse keeps blowing on mine....never had an issue..then one day the fuse started blowing on start up..the game was never moved...stayed in one spot for the last 7 months.....then one day this started happening.

Ive done everything youve done and it still blows.
 
I don't have a cap tester, but I think with a meter on ohms they should read open if good. if you have continuity that implies it's shorted. as noted, C38 is the width cap, it directly ties into the horizontal deflection (and thus high voltage) portion of the monitor. that'll pop some fuses then.

you won't find that on a Randy Fromm flowchart!

I know there's that test for the voltage regulator, but I think you need to sort out your poly cap issues first. if you power the monitor up and it goes into shutdown, then you can suspect the voltage regulator is toast after confirming with a B+ test.

Thanks again for the reply. I am currently searching for replacements for those caps. There's a few more on the chassis like that so I might just pull those too and replace them at the same time. I pulled and tested the R101 and it was fine. I'm going to order a new VR too just to be on the safe side. Fingers crossed that the shorted C37 & C38 were the cause. However, my lack of confidence is having me order some extra fuses. Lol. I will post an update once I have the new parts installed. Thanks again.

Robert
 
I have the exact same problem (u may have seen my threads on it).....no explanation yet as to why the fuse keeps blowing on mine....never had an issue..then one day the fuse started blowing on start up..the game was never moved...stayed in one spot for the last 7 months.....then one day this started happening.

Ive done everything youve done and it still blows.

I've been reading so many posts online that I'm sure I probably read your post regarding the same issue. I will have to go check out your post though just to make sure. But man, that really sucks. I can only pray that I don't have the same result as you in the end. I got so excited when I discovered the C37 & C38 were no good. Once I get my new parts in and installed I will post an update. This is all new to me so I am learning as I go. Tons of reading and youtube videos. I bought 5 used "as is" arcade machines that were all playing blind so I thought a simple cap kit and maybe a flyback replacement would get them all going but so far no luck. Maybe 6 months from now I will have all the games up and running. Who knows, I might even know what I'm doing by then. Lol. Take care.

Robert
 
Thanks again for the reply. I am currently searching for replacements for those caps. There's a few more on the chassis like that so I might just pull those too and replace them at the same time. I pulled and tested the R101 and it was fine. I'm going to order a new VR too just to be on the safe side. Fingers crossed that the shorted C37 & C38 were the cause. However, my lack of confidence is having me order some extra fuses. Lol. I will post an update once I have the new parts installed. Thanks again.

Robert

For what it's worth, I use a 2A circuit breaker like this with alligator clips while repairing monitors. Saves lots of fuses until I track down the short.

Y0wb2Njl.jpg
 
Thanks again for the reply. I am currently searching for replacements for those caps. There's a few more on the chassis like that so I might just pull those too and replace them at the same time. I pulled and tested the R101 and it was fine. I'm going to order a new VR too just to be on the safe side. Fingers crossed that the shorted C37 & C38 were the cause. However, my lack of confidence is having me order some extra fuses. Lol. I will post an update once I have the new parts installed. Thanks again.

Robert

that's a double-edged sword when you blindly replace parts. it's why I for the most part frown upon replacing OEM flybacks (just cause they have white knobs!!) or HOTs simply because they came in the rebuild kit. I would advise only changing the parts that need changing -- it sucks you have to place multiple orders, but you could just grab everything in one shot and save it for a rainy day if you don't need it.

R101 if you've seen in a parts list or schematic is a 6.8k ohm resistor. try measuring that in circuit; if it kinda gets stuck at around 5k and just barely slowly trickles up, it's probably no good. I know it's typically advised to test them out of circuit but that's one instance where I don't care how it measures out, I want to know how it works in. :) R103 is another important one, it's the vertical ceramic resistor nearest to the filter cap.
 
that's a double-edged sword when you blindly replace parts. it's why I for the most part frown upon replacing OEM flybacks (just cause they have white knobs!!) or HOTs simply because they came in the rebuild kit. I would advise only changing the parts that need changing -- it sucks you have to place multiple orders, but you could just grab everything in one shot and save it for a rainy day if you don't need it.

R101 if you've seen in a parts list or schematic is a 6.8k ohm resistor. try measuring that in circuit; if it kinda gets stuck at around 5k and just barely slowly trickles up, it's probably no good. I know it's typically advised to test them out of circuit but that's one instance where I don't care how it measures out, I want to know how it works in. :) R103 is another important one, it's the vertical ceramic resistor nearest to the filter cap.

Yah, that's probably a good idea. The parts are not very expensive so it wouldn't be a big deal to order the extra parts but just hold onto them until they are needed. I keep the working old parts in labeled ziploc bags just in case I'm desperate and need a part that I don't have one day.

As for R101, I tested it out of circuit and it was 6.8k. I'm pulling the diodes and so far D18 and D19 are good. I will post another update later tonight after I finish pulling and testing the others. Thanks again for the reply and help.

Robert
 
For what it's worth, I use a 2A circuit breaker like this with alligator clips while repairing monitors. Saves lots of fuses until I track down the short.

Y0wb2Njl.jpg

Man, that thing would be great. So you can order those in different amps and as a slow blow too? Where do you buy them?

Robert
 
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