Author Topic: Kortek KT-2182 chassis - not turning on (worked fine a few days ago) (Read 15154 times)

Midcoastsurf · « **on:** January 30, 2013, 12:15:11 am »

Hello,

I have a Kortek #KT-2182 chassis. The monitor was working fine with no issues. I turned the game on last night and the monitor did not come on. I tried different plugs on the powerstrip and even plugged it into the extension cord directly without any change. I removed the VGA plug from the computer, hoping to see a "no signal" on the monitor, but the monitor remained black. I measured the voltage at the plug going into the monitor board and it read between 119-120 vAC. I also pulled out the little fuse right behind the power plug on the monitor and it checked out OK on the DMM. I have the chassis pulled and will be testing the HOT within the next day or two. I noticed the big brown 330uf cap has a slight rounded top to it. Cause for concern? (not sure what it does).

Any ideas?

Thanks

lilshawn · « **Reply #1 on:** February 01, 2013, 01:44:09 am »

while i don't know anything about this particular monitor, some general basic things you can check are:

power up the monitor for a few seconds and then wile looking at the screen, pull the plug. Does the screen flash as the power is cut?

if it does, the monitor is working. if nothing we need to dig deeper.

power up just the monitor... can you hear any noises from the monitor however faint it might be? clicking? chirping? buzzing? explosions?

if you hear something your monitor is attempting to startup, but a problem is preventing it.

if you hear nothing, the power supply is dead. it will need to be repaired.

Midcoastsurf · « **Reply #2 on:** February 01, 2013, 02:24:12 am »

lilshawn,

Thank you for the reply! I powered up just the monitor and I can't hear anything...no buzzing, humming, chirping, nothing. There is no difference in sound when it is plugged in or unplugged.

When you refer to the "repairing" power supply, what does that usually imply? I was under the impression that the power supply is just one big unit, but there are possibly other components that get replaced at the same time? I have pointed to what I believe to be the Power Supply on this chassis (this is not my actual chassis, just the picture from the manual). I have done board work, but only on pinball machines.

Thanks

lilshawn · « **Reply #3 on:** February 01, 2013, 10:52:01 am »

basically everything from that transformer south is the main power supply. It is of the "switch mode" variety. I'll explain briefly how it works so you can test it properly.

You have 4 main parts to a switch mode power supply (SMPS)... a conversion stage, a control chip, a switching MOSFET, and the transformer.

first, the AC from the wall outlet flows into the chassis through the cord and flows through the conversion stage. this is usually a bridge or set of diodes that convert the Alternating current (AC) to a direct current (DC) we now have somewhere around 100 volts of DC.

the next thing that happens is the DC flows to the MOSFET (in the photo - attached to the heatsink below the transformer you pointed out). a MOSFET is like a switch that can turn on and off VERY fast. many 1000's of times a second. we will get back here in a minute.

what also happens is a small 8 legged control chip starts to operate. what it does is monitor the voltage of the system and opens and closes the MOSFET switch very fast. if it senses the voltage going down, it holds the switch open slightly longer, if it goes up, it leaves it closed a little longer. this is called DUTY CYCLE. our constant stream of DC voltage is now being very quickly pulsed.

the output from the MOSFET is now pushed out to the transformer you pointed out in the photo. the high frequency pulses are converted to different voltages by this transformer. (5 volts, 12 volts 70 volts, 140 volts.) for use by the monitor. this section i described is the power supply.

the MOSFET and the control chip have protection built into them to keep from being damaged due to a fault. the chassis will sometimes emit a squeek, squeel or chirp if there is a fault. this is due to the system trying to start up and shut down because of the fault. it senses an issue, shuts down, then tries again...many times a second. usually this is audiable but not always.

you are going to want to check and make sure the MOSFET is switching.

DISCLAIMER

there are some nasty voltages that could kill you if you touch them. use caution when working an open chassis. avoid the large wire suction cupped to the tube and the AC voltages coming into the chassis. generally avoid touching ANYTHING unless it's with a meter probe.

the conversion stage is likely okay since a fault here will often blow the fuse. so we will test the switcher an see what we have. this isn't going to be easy. it might be best to use some alligator clip wires (something like this: http://www.asia.ru/en/ProductInfo/998804.html to attach the meter probes since it isn't particularly safe to reach in there while it's powered (working or not)

the MOSFET has 3 legs, an input leg, an output leg and a switch leg. called the GATE the SOURCE and the DRAIN. most mosfets have the legs oriented in the order from left to right (when looking at the writing on it) Gate, Source, Drain (GDS). what you need to do is clip the red meter lead onto the middle drain leg and the black lead onto the ground of the chassis. (basically any metal part.) you want to make sure the clip touches nothing but the leg and NONE of the other legs. TRIPLE check. set the volt meter to read voltage over "200 volts DC" sometimes it's best to set the meter to it's maximum rating to be safe if the voltage is unknown.

power up the monitor and see what you have. it should read pretty steady. if nothing, the MOSFET or the switcher chip are bad. if it's all over the place with seemingly random readings it could still be bad or there is something else down the line wrong.

Midcoastsurf · « **Reply #4 on:** February 01, 2013, 05:23:41 pm »

Thanks lilshawn! So the MOSFET is the first component that the power flows into on the chassis. If this does not switch on properly, then power does not continue to flow to the power supply, which then changes the voltages and re-distributes the power.

Hopefully this isn't a stupid question, but can I power up the chassis without the monitor board being plugged into the tube? It would be a little hard to test the MOSFET if chassis was in the game.

Thanks

lilshawn · « **Reply #5 on:** February 01, 2013, 07:11:53 pm »

not exactly, an SMPS must have a minimum load attached to it in order for it to properly regulate the voltage. it's a bad analogy, but think of it as a balloon with a hole in it attached to a bicycle pump.

air is electricity, you are the controller chip, the pump is the MOSFET and the balloon is the transformer. you must pump the baloon and keep it at a, say, 1 foot diameter.

as you pump air into the balloon, the air just goes out the hole...you can pump and pump as hard and fast as you can and never inflate the balloon. this is the power supply with NO LOAD attached.

But, if there is something plugging the hole, (the load) it will still leak, (because power is getting used up) but you can still get the balloon to inflate slightly. how much of this hole is covered depends on how fast you must operate the pump to keep the balloon the same size. this is basically how the SMPS regulates itself so the proper power level is produced.

as much of a pain in the butt it is, i highly recommend removing the monitor... tube and all... from the cabinet. it will make diagnosis and testing...and subsequent repairs and testing much easier. it can be done in the cabinet, it will just take a little longer.

you may still have an issue with the bridge rectifier, (conversion stage) even though the fuse isn't blown. I'm just doing things in order of "likeliness of failure".

Midcoastsurf · « **Reply #6 on:** February 01, 2013, 09:43:08 pm »

I got a reading of 79.5 vDC...little to no fluctuation.

lilshawn · « **Reply #7 on:** February 01, 2013, 10:09:37 pm »

also, what is the power LED on the control panel doing? is it on off blinking dim?

okay what about the seconday output of the transformer....

check the following DC voltages at the cathode side of the following diodes (cathode is the banded side) positive meter lead on the diodes and the black on ground.
D107 (14v)
D110 (6.3)
D120 (80V)
D121 (220V)

Midcoastsurf · « **Reply #8 on:** February 01, 2013, 11:36:15 pm »

I wrestled the tube out of the machine....I LOVE big tubes! I hook it all back up to test the voltages, plug it, ta-dah! It's working again. Hmmmmm. I checked the voltages you mentioned:

D107 = 12.4vDC
D110 = 2.6vDC
D120 = 86.0vDC
D121 = 210.0vDC

Loose connection somewhere?

ed12 · « **Reply #9 on:** February 01, 2013, 11:57:26 pm »

what we call a :hair line crack: and or : a bad solder joint:
take yer pick

ed

Midcoastsurf · « **Reply #10 on:** February 02, 2013, 12:07:21 am »

Would these most likely be at the connectors on the chassis? I'll start reflowing the solder beginning with the power plug socket on the chassis. Thanks.

ed12 · « **Reply #11 on:** February 02, 2013, 12:44:41 am »

yep

ed

lilshawn · « **Reply #12 on:** February 02, 2013, 12:49:16 pm »

the 6 volt is a little on the low side. better reflow the neckboard solder connections too. especially around the socket that plugs onto the tube.

the 6 volts is usually used to drive a heater inside the tube. make sure the neck board is on securely.

all the other voltages looks good.

you didn't by chance move the cabinet before it stopped working did you. I'm probably looking too much into this, but it seems like the heater might be grounded out (either the wire leading to it, or inside the tube.)

I'll go over the schematic later today and see what else runs off that 6 volt line. Could be a bad 5 volt regulator used for the digital circuits runs off that too.

ed12 · « **Reply #13 on:** February 02, 2013, 01:05:51 pm »

i took note of the 2v comming from d110??
if that is the heater voltage try reading it again in ac mode instead of dc mode
your reading's
D107 = 12.4vDC
>>>D110 = 2.6vDC<<<
D120 = 86.0vDC
D121 = 210.0vDC
what the manual call's for
D107 (14v)
>>>D110 (6.3)<<<
D120 (80V)
D121 (220V)
chk for a short in the circuit
also on them chassic that big ic at the front with the paper covering it
can and will go south without any warning

ed

lilshawn · « **Reply #14 on:** February 02, 2013, 01:21:28 pm »

looks like killing the 6.3 volt powers off the monitor for some reason. there is a digital power off signal the comes from Q104 and drives Q105. could be some protection circuit or no signal suspend in IC501.

check for a faulty R118, R122, R123 check for discolored cases or burn marks on them.

R118 - 1.3 ohm
R122 - 47k ohm
R123 - 1k ohm

also if you have one available change C118 (470 uF 16 volts) it could be dragging down the volts too.

ed12 · « **Reply #15 on:** February 02, 2013, 01:43:22 pm »

ya i was just looking at my ppw
it is shut down control
i will stand down for now as this get's real tech for the test's.which i know
and have proven

lilshawn
the show is your's for now
i will just keep an eye on it

the smp's is working just fine
something is loading it

ed

Midcoastsurf · « **Reply #16 on:** February 02, 2013, 06:19:01 pm »

OK, just got done re-flowing connections on the neck board and chassis. I also noticed I originally measured D105 and NOT D107.

D107 = 13.6v

R118 = 0.3 ohm (I removed one leg from the circuit to test). this is a 1.3 ohm resistor, so shouldn't it test 1.3?

R122 and R123 did not have resistors and don't ever appear to have been used on this board.

The monitor is working after re-flowing everything and checking the resistor...phew. My only concern is the low voltage at D110. It still measures 2.6v DC. Could this be caused by R118?

Thanks

Midcoastsurf · « **Reply #17 on:** February 02, 2013, 08:18:23 pm »

I put the tube back in the game, fired up the monitor....nothing. No voltages at any of the big diodes. No sounds at all.

lilshawn, yes I do have to move the game out a little from the wall to turn it on since the switch is at the back of the game. The game does get bumped around a little, but I feel that problem has to be a loose connection somewhere. I tried lightly moving the power connector on the board, but that didn't make any change.

ed12 · « **Reply #18 on:** February 02, 2013, 09:02:49 pm »

is there a in-line fuse ?
to the ac of the monitior ??
if so chk it
un-plugged of course

ed

lilshawn · « **Reply #19 on:** February 03, 2013, 12:22:57 am »

damn, i hate when stuff works on the bench then doesn't once it's back in the machine.

D105/107 are basically in the same circuit. it's alright.

i also wouldn't worry about missing components, they change stuff all the time.

0.3 ohms doesn't sound right... are you sure it's 0.3 ohms not 0.3k ohms (300 ohms)? you have to be careful of what range the meter is set to.

What colors are the stripes on this resistor? (should be Brown/green/black for a 1.2 ohm) if it's something else, we should go by that. Use caution though, the high heat generated by this resistor can cause the colors to, well, discolor. (black/black/black)

i'm still suspect of C118 (470 uF 16 volts) anything bigger voltage (16/25/35/50 volt) would be fine to use as long as it fits in the space. keep the same uF rating though. bad caps can cause all sorts of weird problems. be sure to note which side is positive and which is negative and install the replacemet the same, otherwise big boom boom.

dig around your house and see if there is a cap you can steal from something (old computer card/telephone/tapedeck) and swap it out.

Midcoastsurf · « **Reply #20 on:** February 05, 2013, 08:28:42 pm »

Ed12:

There is a little fuse - 3.15A I pulled it and it tests good on the meter.

Lilshawn:

I am still on the lookout for a 470uf cap. I have found 10's, 22's, and 220's. Anywhere else on the board I can look in the meantime? I will also check out the resistor value at R118.

Thanks

lilshawn · « **Reply #21 on:** February 05, 2013, 09:03:44 pm »

You can check the HOT. I don't think it's your problem but.... do a continuity test between the ground on the board and the middle leg on it. it should read open or very high resistance.

if it reads a "short" (0 ohms) or low resistance, it's bad.

also check between the 2 outside left and right legs. try reversing the leads and checking again. it should read open or very high resistance.

if it reads a "short" (0 ohms) or low resistance, it's bad.

if You have an issue in your electronics that's causing the no power, we will have to dig a little deeper. something on that 6.3 volt line is dragging down the voltage. what's on the line... that 470uF cap, and a few transistors being used as switches. mainly, the heater, a tiny bit of a vertical system (vr701 after the voltage is dropped a tiny bit) and that's about it. could be a fault in one of the transistors...unlikely though but still possible.

i would lift out R118 and re check the voltage and see if it's popped back up to 6.3 volts. if not, that cap (c119) is toast and needs to be changed. if it springs up to 6.3 volts again, the problem is further down the line.

Midcoastsurf · « **Reply #22 on:** February 06, 2013, 02:36:46 pm »

I checked voltages before and after pulling R118. The voltages did not change without the resistor being in the circuit.

D107 = 0.47v
D110 = 0.0v
D120 = 0.02v
D121 = 0.04v

Here is the picture of the area with labels.

Midcoastsurf · « **Reply #23 on:** February 07, 2013, 11:39:41 am »

Found a bunch of 470uf caps...but they are 6.3v

lilshawn · « **Reply #24 on:** February 07, 2013, 10:27:44 pm »

Quote from: Midcoastsurf on February 07, 2013, 11:39:41 am

Found a bunch of 470uf caps...but they are 6.3v

yeah, that's a little close.

even though the voltage is 6.3 volts, you always want at least a 2x overhead. 6x2=12volts...closest cap up from that? 16volts.

also when "scabbing" caps from other things, pay attention to the temperature rating. older caps are rated for 85 degrees. it can sometimes get hotter than that, so it's best to use the next rating up from that - 105 degrees.

it becomes important if the cap is sitting next to a heatsink or other hot component.

Midcoastsurf · « **Reply #25 on:** March 02, 2013, 05:49:56 pm »

OK, finally installed a fresh 470uf cap at C118. Thanks Robert! The monitor powered up, but I realized I had put the yellow/green connector on backwards (text on screen read backwards). I reversed the connector and the monitor did not power on again

I tried reversing the connector again and the monitor still did not power on. The fuse is good...I am actually using a circuit breaker in place of the fuse until I can get everything sorted out. Could this be a grounding issue? I ask this because the chassis is not securely mounted to the bottom plate (as I keep moving the chassis in and out of the game). Although, the chassis worked fine when not grounded outside of the game and hooked up to the tube (tube was also outside of the game).

Next thing to try?

Thanks

arcade nut · « **Reply #26 on:** March 02, 2013, 07:12:22 pm »

your welcome bud, make sure you have line voltage going into the board,, (120VAC) I have spent many hours looking for a problem like that and the plug was dead

Midcoastsurf · « **Reply #27 on:** March 02, 2013, 09:23:20 pm »

I just measured the voltage at each side of the fuse clip on the chassis and it reads 120.8 ACV at both sides.

I also noticed your post about the 2932F, this is the same monitor I have, but my chassis also has a sticker that says 2182...which the schematics are available for online. I gotta go fix dinner, but let me know if you can't find it.

Thanks

Midcoastsurf · « **Reply #28 on:** March 04, 2013, 12:16:54 am »

I double checked the resistor at R118 with one leg removed and my DMM set to 200 Ohm and it reads 0.3 to 0.4. Definitely lower than the rating of 1.3ohms.

lilshawn · « **Reply #29 on:** March 04, 2013, 09:49:08 am »

ususally when resistors go bad they go up in resistance or go open.

Quote

I just measured the voltage at each side of the fuse clip on the chassis and it reads 120.8 ACV at both sides

as in - one meter probe on each side of the fuse? or one probe on ground and one probe testing each side.?

Midcoastsurf · « **Reply #30 on:** March 04, 2013, 10:30:55 am »

One lead on ground and the other at a fuse clip. Test both sides of the fuse clip. Should I test it differently?

Thanks

lilshawn · « **Reply #31 on:** March 04, 2013, 01:17:18 pm »

no no, I was just confused... it sounded like you had tested by placing a probe on each side of the fuse. if you had gotten any voltage that way, your fuse would have been open.

i would also be suspect of the capacitor that is tucked inside that heat sink in the photo you posted. i don't know if it's actually in there or it's a camera trick... but it's going to be mighty hot in there if it is.

Midcoastsurf · « **Reply #32 on:** March 04, 2013, 03:20:48 pm »

That cap is not tucked inside the heat sink, it's an unintentional camera trick. Good catch!

I'm off to order the resistor.

Thanks

lilshawn · « **Reply #33 on:** March 04, 2013, 05:49:03 pm »

when you change that resistor (because it gets so hot) you'll want to get rid of all that old solder and clean up the pads real good. The old solder is oxidized and won't stick properly to everything it's supposed to.

Midcoastsurf · « **Reply #34 on:** March 04, 2013, 08:54:44 pm »

Thanks for the tip! The old resistor was secured to the large heatsink with a glob of silicon. Is this necessary when I install the new resistor?

lilshawn · « **Reply #35 on:** March 04, 2013, 09:00:21 pm »

naw, it's mostly to keep it from rattling loose during shipping.

Midcoastsurf · « **Reply #36 on:** March 10, 2013, 12:30:28 am »

I installed a fresh 1.2 ohm, 3W resistor at R118. I also replaced about 10 caps on the chassis (I had the values that were on the board, so I replaced them). I did make sure to clamp on a heat sink to the leg of the cap I was soldering.

I hooked the chassis up to the tube and chassis powered up and the monitor makes that static sound (normal i believe). The only problem is there is no picture on the monitor...it should say "no signal" when the VGA connector is not hooked up to the computer. I tried the VGA plugged in and still nothing. The front of the tube where the picture should be is black.

I was able to plug in the monitor and unplug it about 5-6x over a 10 minute period and the chassis consistently powered up.

Any ideas on where to look now?

Thanks!

lilshawn · « **Reply #37 on:** March 10, 2013, 12:35:15 am »

are you getting the heater on in the neck? (orange glow)

if not, you have an issue with the 6.3 volts powering it.

Midcoastsurf · « **Reply #38 on:** March 10, 2013, 12:40:22 am »

Wow...I came back to edit my reply and you had already responded. You're quick!

The red wire that runs from the flyback to the white plastic piece on the neck board was pulled out of the white plastic housing on accident. (when I removed the tube and forgot to unhook a wire

I pushed the red wire back into the white plastic piece, but maybe the connection isn't good enough or something needs to be repaired/replaced? It has powered on before since the accident and the tube showed a picture...but I still had the intermittent chassis issue of not powering on at all. Is this red wire the one that supplies the 6.3v?

Thanks

lilshawn · « **Reply #39 on:** March 10, 2013, 01:31:27 am »

no, that's going to be the focus. though not likely to cause a blank screen, i've seen weirder though.

still check your heater. no heater will cause blank screen for sure.


Main	Restorations	Software	Audio/Jukebox/MP3	Everything Else	Buy/Sell/Trade
Project Announcements	Monitor/Video	GroovyMAME	Merit/JVL Touchscreen	Meet Up	Retail Vendors
Driving & Racing	Woodworking	Software Support Forums	Consoles	Project Arcade	Reviews
Automated Projects	Artwork	Frontend Support Forums	Pinball	Forum Discussion	Old Boards
Raspberry Pi & Dev Board	controls.dat	Linux	Miscellaneous Arcade	Wiki Discussion	Old Archives
Lightguns	Arcade1Up	Try the site in https mode		Site News


Unread posts \| New Replies \| Recent posts \| Rules \| Chatroom \| Wiki \| File Repository \| RSS \| Submit news