Magnavox DRV power supply SMPS

[momaka]

Re: Magnavox DRV power supply SMPS

The MOSFET going bad.

Since you had the bulb in series with the PSU while testing the mod board, that means the MOSFET and resistor must have been bad before that. This also happens to coincide with why the bulb kept staying On before that.

[johnfin]

Re: Magnavox DRV power supply SMPS

Resistors came today. Installed .68ohm resistor and same results: no light and power is getting to board. Circuit breaker ok, power to board, resistor and mosfet new. No power at ouput. Whats the next test?

[momaka]

Re: Magnavox DRV power supply SMPS

Measure the DC voltage on the main cap. Should get about 160-170V.
- If not, let us know. Check fuse F2001
- If yes, check the DC *voltage* on both sides of R2101 and both sides of R2106. Also check voltage on pin 6 (Vcc) of the NCP1200 controller. (on that note, did you replace the NCP1200 after the last test when the PSU smoked?)

[johnfin]

Re: Magnavox DRV power supply SMPS

cap = 160vdc
fuse good (of course)
pins 6 and 4 of 1200 = 7vdc (yes replaced)
when measuring resistors, can I use neg of big cap for ground, then each side of resistors.

Frankenboard coming alive, right?

[momaka]

Re: Magnavox DRV power supply SMPS

cap = 160vdc
fuse good (of course)

Good.

pins 6 and 4 of 1200 = 7vdc (yes replaced)

pin 4 is primary-side ground - i.e. tied down to the negative (-) lead of the primary-side input cap (the main cap). So you should *not* see any voltage on it.

Meanwhile, pin 6 (Vcc) should be somewhere between 9.8 and 11.4V (10.6V average) while the IC is working. 7V DC is too low for the IC to start, so that indicates either the IC is detecting some fault or its not getting proper power.

With that in mind...

when measuring resistors, can I use neg of big cap for ground, then each side of resistors.

YES.
Always use the negative lead of the big cap when measuring voltages on the primary side.

The fact that there is some voltage on pin 6 (Vcc) with respect to the (primary) ground means R2101 is probably good, but still check it.

Checking voltage on both side of R2106 is also important to make sure we are supplying the IC with high enough voltage (minimum 30 volts needed on pin 8, HV).

Frankenboard coming alive, right?

Yes.
The fact that you have some voltage on the Vcc pin of the NCP1200, that nothing is blowing up/smoking anymore, and that the incandescent series bulb is not coming fully On means we are getting there. Slowly, but will happen eventually.

So like I mentioned in the beginning, at least with this mod you won't blow more components if there is something wrong with the circuit. The PSU may look "dead" with not voltage outputs, but measuring the voltage on its Vcc pin may give a good indication of what's going on.

[johnfin]

Re: Magnavox DRV power supply SMPS

4&6 of the 1200 means I went across them to get the voltage. =7vdc

R2101 is a HUGE ceramic resistor, ohms fine and measured each side to neg on main cap = 167vdc

R2106 is a smd, no real voltage measured from each side to neg on main cap
ohms fine

All resistors in series with 2106 ohm out fine.

So whats next?

[momaka]

Re: Magnavox DRV power supply SMPS

R2106 is a smd, no real voltage measured from each side to neg on main cap
ohms fine

All resistors in series with 2106 ohm out fine.

Hold on, other resistors in series with R2106??? R2106 should connect directly on one side to pin 3 of the main transformer and directly to pin 8 (HV) on the NCP1200 chip.

Did you replace the orignal SMD R2106 resistor (and remove the other series SMD resistors) from the original design with a 22 KOhm resistor as I drew on the schematic?

If not, that definitely needs fixing. Pin 8 (HV) of the NCP1200 chip needs at least 30V for the chip to work. If the resistance is too high, that would cause the NCP1200 to have low Vcc voltage and not turn On.

[johnfin]

Re: Magnavox DRV power supply SMPS

ok, you threw me a curve. I was looking at r2106 on the board. they are all disconnected. the 22k (its good)is new and connected to pin 8. What resistance and wattage should I try?

[momaka]

Re: Magnavox DRV power supply SMPS

Sorry about that. When I was drawing the schematic for the mod board, I reused one of the resistors for R2106 and forgot to remove the "R2106" designator on the board, so that's what probably got you confused.

the *new* R2106 (which doesn't even need to be placed where R2106 is), should be 22 KOhms and I think 1/2 to 1W power rating will be more than enough. Give that a try and lets see if there are any voltage outputs.

[johnfin]

Re: Magnavox DRV power supply SMPS

the 22k is what you called for and what it is. needs to be lowered i guess. any thoughts.

[momaka]

Re: Magnavox DRV power supply SMPS

Try 10k then. I doubt that's the issue, but nevertheless.

[johnfin]

Re: Magnavox DRV power supply SMPS

you were right, didnt work. Paralleled a 18k to get 9900ohms and pins 4-6 read 7.14vdc. Whats next.

[momaka]

Re: Magnavox DRV power supply SMPS

What's the voltage on both sides of R2106 (relative to primary-side ground)?
Also, what's the voltage on R2108 on the side that is connected to MOSFET Q2101? (Again, relative to primary-side ground.)
We need to understand why the IC is not switching and why Vcc is so low.

**EDIT**
Looks like the IC might be stuck in protection mode either due to over-current overload or the start-up cap is too small, causing the IC to think the PSU has a short-circuit on the output. But let me know what voltages you get for the above items so we can get a full picture of what's going on.

[johnfin]

Re: Magnavox DRV power supply SMPS

R2106 = 157/154vdc

R2108 = zero both sides

was taken to - side of main cap.

[momaka]

Re: Magnavox DRV power supply SMPS

Sorry for the delay in response, I was traveling again.

I looked at the datasheet again, and it appears the IC is indeed stuck in short-circuit protection, given the readings above. You can make R2106 back to 22 kOhms again.

After that add another 10 uF cap with the 10 uF cap already there (for a total of 20 uF). If that doesn't work, up the capacity to 30 uF (3x 10 uF capacitors in parallel) or just use a single 33 uF cap if you have one. If that doesn't work, then try 47 uF last. For each of these, measure the output voltage of the PSU. And if the PSU does *not* work, measure the voltage on both sides of R2106 and also on pin 6 (Vcc) of the IC. Hopefully, this should give us more clues for what to change next.

[johnfin]

Re: Magnavox DRV power supply SMPS

22K back
10uf added to 10uf in parallel

results
2106 = 157vdc 148vdc
2108 = zero

pins 4&6 = .06vdc

========================

added 22uf to existing 20uf caps in paralled

same but pins 4&6 went up to .1vdc

[momaka]

Re: Magnavox DRV power supply SMPS

22K back
10uf added to 10uf in parallel

results
2106 = 157vdc 148vdc
2108 = zero

pins 4&6 = .06vdc

========================

added 22uf to existing 20uf caps in paralled

same but pins 4&6 went up to .1vdc

Hmmm...
But in post #164 (with the original 22k and 10 uF cap), you said you had 7V DC on pin Vcc of the NCP1200 IC?? Can you verify that measurement again?
It doesn't make sense for the voltage of the IC to fall down that low with the parallel caps. Please check and report back.

[johnfin]

Re: Magnavox DRV power supply SMPS

So your mighty 1200 chip is not so mighty. I removed the additional caps, 22k resistor in tact, still no voltage so I replaced the 1200 and guess what, 10volts on pins 6-4. I removed the chip so that I dont blow thru a dozen of these figuring things out. Back to square one.

[momaka]

Re: Magnavox DRV power supply SMPS

So your mighty 1200 chip is not so mighty. I removed the additional caps, 22k resistor in tact, still no voltage so I replaced the 1200 and guess what, 10volts on pins 6-4. I removed the chip so that I dont blow thru a dozen of these figuring things out. Back to square one.

Well, your voltage measurements seem different every time, even with supposedly the same parts. That doesn't happen very often, which makes me suspect either your equipment or your measuring techniques... especially given the thread history in the first few pages.

10V means the chip is working along with the rest of the PSU (actually should be 10.6V, but that's still close enough and within range... are you rounding voltages, though? If yes, please don't.) Did the PSU have no output then?

With results like these, I honestly feel that were getting close to the point where I'd rather you send the PS to me or someone else here (if anyone is willing) so that we can get it running for you. Heck, I'm even willing to pay for the return shipping just to get done with this thing.

I mean no offense, as i know you came here to get your PS fixed and maybe even learn in the process... but without good repeatable results, we can't really get anywhere.

[johnfin]

Re: Magnavox DRV power supply SMPS

Well since you have not answered any PM's or emails in the last 179 posts I wont hold my breath or waste my time with you anymore, phony baloney.

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