Old school Fortune Magic Green 14" S/N 96097669 CRT

[Th3_uN1Qu3]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

Congrats on getting the PSU running. It seems like you have more trouble ahead however...

I would first check if the flyback transformer is operating. You said the HOT checked fine. Then see if you get any voltage outputs from the flyback. There will be a number of low voltage rails generated by the flyback, you can check those. Look for traces under the FBT leading to diodes, and measure voltage after those diodes.

PS. CTX was a good CRT monitor brand. Rebadged means renamed. CTX made it for a customer, hence the different branding.

[senz_90]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

If zener checks OK in circuit, it is good. No need to remove it. Yes the startup resistor can fail too, but less often. A voltage of 0.7v on Vcc makes me think of the 3842 chip itself rather than the startup resistor.

This is a common power supply circuit for a lot of things, not just CRT monitors. You should learn this circuit by heart as you're going to see it a lot.

first at all thank you for your reply..
Because I am hobbyist where usually on ATX PSU, so didn't know much about this IC. This is a good thing for me to learn different PSU. Today i buy the replacement. Changes start up resistor though checks good, 2 resistor near current sense resistor because analog VOM too bad about precisement, the IC with KA3842BN.

I am connect a series light bulb to make sure, turn it on and the bulb dim . Yeah, this is good sign, so i am remove the bulb and try turn it on. power button led is lit !! no picture..

at least but not last, I know those PSU section is running well now. I am trying to measure voltage on B+ flyback and get ~100VDC. I am afraid to measure others pin according to my max VOM range just 1KVDC, maybe it could damage something when wrong measurement.

so how do you think the rest? the problem is in RGB board or not? I guess it has cold solder joint or anything that makes no picture symptom.

the original mosfet got really hot to scorch a heatsink print on the board.
btw this is probably a rebadged chuntex(ctx).
at least you have the hitachi tube.lots of the rebadged versions got the blue label samsung which were garbage.

Yeah the mosfet fryed very bad and cracked on code number also the print board.
what is rebadged chuntex(ctx) ?
GOOD EYES!! did you see hitachi label on the tube?
how do you think about these two tubes? what is the better tube?

[kc8adu]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

the original mosfet got really hot to scorch a heatsink print on the board.
btw this is probably a rebadged chuntex(ctx).
at least you have the hitachi tube.lots of the rebadged versions got the blue label samsung which were garbage.

[Th3_uN1Qu3]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

If zener checks OK in circuit, it is good. No need to remove it. Yes the startup resistor can fail too, but less often. A voltage of 0.7v on Vcc makes me think of the 3842 chip itself rather than the startup resistor.

This is a common power supply circuit for a lot of things, not just CRT monitors. You should learn this circuit by heart as you're going to see it a lot.

[senz_90]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

fortunately someone wanna give me respond after confused around 2 days, thank you very much, i am appreciated your reply much because i have no experience at all on CRT.

yeah, i am just download datasheet and read about this IC, it says that need about 16V to start at some website. and it was also mention about my start up resistor 100k maybe failed to higher ohms. so i have to tracing source and gate trace and changes all resistor corresponded. this is a new information !! thank you !!

i'll keep update and after have a time i'll try to draw the schematic. is there any chance that Zener diode near IC failed? it checks not bad in circuit but it doesn't make me sure. I will buy a new IC and resistor today, also zener diode if it checked defective off circuit.

[Th3_uN1Qu3]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

If the mosfet was shot then usually the source and gate resistors go with it. Replace those. Replace UC3842 also, it is likely dead. UC3842 needs a minimum of 16v to start, check the datasheet. Google will help you. That MOSFET will work okay, focus on fixing the rest of the circuit before ordering a better part there.

[senz_90]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

okay, since i read about fet replacement, it seems like i have to get a lower Rds, also lower input capacitance for replacement, but voltage and ampere is better to higher.

i compare this 2 fet datasheet and it has 0,8 ohm difference and higher (not good), more resistance more power has to dissipate..

I think this is not too bad since i am attach a new thermal grease on the heatsink, so i am soldering it in and replace all bad components. turn it on and power button led doesn't lit nor picture tube. try to figure out what happens....

measure voltage across two diodes rectifier before rectifiering, got ~220VAC. so it looks my filtering and new fuse is okay. next step were trying measure across filter caps get ~290-310VDC so it looks like fine, tracing next from this caps, get a DC voltage on Drain Fet, Gate and Source no voltage, but after B+ caps it has series 100k 2W resistor and just ~0,7VDC i got and the trace is connected to pin 7 Vcc UC3842 PWM IC. I don't know exactly what Vcc voltage should i get for make output from this PWM IC.

also try to measure secondary diodes, no voltage !! so it stuck on primary, didn't know exactly is PWM IC failed or not, so I am trying to draw this schema, i'll post this diagram later. question in my head is mosfet didn't matched or the PWM IC has failed? what do you think?

[senz_90]

Re: Old school Fortune Magic Green 14" S/N 96097669 CRT

well, it looks like this old CRT monitor was obsolete so nobody interest, i have know the different between MTP6N60 and FQP6N60A on their datasheet, one has zener diode across drain and source, the other just a common diode across drain and source. would it makes different to replace this one?
I am just afraid of BANG accident if didn't matched. I don't know exactly what typical rate to compare when replace a MOSFET, newbie , i have read on googling but didn't sure enough it is right or not.

if hard to understand my bad english, please confirm me and I'll make some effort to clear it.
there is nobody freakin' CRT Monitor anymore??

[senz_90]

Good day everyone.
I have this CRT monitor laying down in my warehouse so I am just try to fix it, after makes some effort to dig into CRT monitor troubleshooting knowledge, I am open it up , discharge tube and looking around mainboard and RGB board.
The symptom of monitor : no picture, no sound, not even led on power button lit.

After open it, found these :
1. Open Fuse
2. Fryed FET = MTP6N…. (can't see rest number ,cracked on right side) on primary PSU
3. Burned and changes color almost black, polyester caps = 842J 400VMpp right beside HOT
4. Shorted 1N4148 diode on primary PSU
5. High ESR value lytic 100uF 160V
6. Nothing else were look abnormal include good physic of flyback transformer.

What I have done because it just look like a PSU symptom but not to overlook :
1. Changes diode and fuse with same rating and number also buy new replacement.
2. Changes badcaps with Rubycon 220uF 160V.
3. Checks all component near fryed FET trace include 4 mains diode rectifier, others is okay.
4. Checks primary winding PSU transformer and near HOT (didn't know exactly function of this circuit) with flyback tester no problem.
5. Checks HOT and flyback B+ and Collector (primary winding) with flyback tester no problem.

I have buy FET with number code FQP6N60A because guess it was MTP6N60, couldn't find 824J 400V caps on my town.

So after this, I want to ask question from this amazing forum members.
a. Could I changes with this FQP6N60A FET?
b. Instead 824J caps, I have two 474J caps, is this okay if I am make it paralel to change this caps?
c. I have read about X-ray Radiation dangerous and haven't HV probe to measure the anode cup.
How to avoid and adjust this X-ray Radiation with decent tester?
d. Is there a problem changes badcaps with 220uF value (haven't experience on Monitor PSU)?
e. Is there any chance on this case the PTC has failed? It couldn't measured with VOM.

sorry for blurry picts from Android 2MP camera. any advice and suggest very appreciated please
I think so useless to laying down this girl in warehouse