Re: Sony Trinitron E450 bad contrast 15-20 minutes after turning on
Your BVM-1454 could have a bad cap in the heater circuit. It could have other bad caps. Very dim display is a symptom of this. There could be other issues that cause a very dim display. A bad filter cap on the heater voltage supply leads to a low voltage applied to the heater, which results in cooler cathodes and less electron emission. I have a CPD-200GS that had this problem and a few other Sonys I don't recall the models of.
When I repaired that CPD-200GS, I probed the CRT neck...
Ken256
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Last Activity: 02-12-2021, 08:01 PM
Joined: 10-13-2009
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Re: Sony Trinitron E450 bad contrast 15-20 minutes after turning on
One fault I've seen on Trinitrons from this era was bad power supply filter capacitor for the CRT heater. Usual symptom will be a dim or dark display. Not sure if that describes your symptoms. Heater should be 6.3 volts.
Probing live CRTs can be tricky (don't slip!) The service manual has a diagram (1.3) showing the main board in the "service position." The CRT neck pins should be accessible. You can probe the heater and cathodes with a DMM or oscilloscope. The grid/focus/screen...Last edited by Ken256; 01-26-2021, 07:23 PM.Leave a comment:
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Re: CRT image Tweeking? Viewsonic PS790.
I thought an aged CRT would show a dim and blurry image. But this CRT is bright and sharp overall. It is just low-brightness images are blueish.
I did look at the service manual and saw a data port. I imagine the adjustment software is long gone....Leave a comment:
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CRT image Tweeking? Viewsonic PS790.
Hello. I have some nice CRT displays. Its been some time since I have used them. The Viewsonic is actually working very well. But, I noticed a minor issue with the image.
Images with an overall, low brightness appear very blue. Instead of dark gray, it is dark blue. With a full black raster, the screen is a very dark blue.
I also have a Sony CRT monitor which does the same thing, except dark imagery has a distinct red tint.
For full-brightness imagery the screens appear to have excellent color balance.
I was thinking this could be... -
Re: Viewsonic VP171b, orange screen, flickers
OK. Thanks for sharing your CCFL pictures. Looks more like a bad CCFL bulb. Maybe not worth replacing bulbs. I'll pull them out and look. Thanks....Leave a comment:
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Viewsonic VP171b, orange screen, flickers
Hello. I have an old Viewsonic VP171b. When first turned on the picture had a very orange color. Within 30 seconds the orange color improved, but some orange tint remained. There was also a slight, repetitive flickering of the image. After 15 minutes all of these symptoms disappeared and the image was perfect.
I have seen old laptops with permanently orange screens. I assumed this was caused by worn out CCFL bulbs. But I have never done CCFL replacement.
It seems the VP171b has some warm-up or temperature dependent problem. The thought occurred to me that the power... -
Re: Samsung LE37A556 Screen Fades to white / Bleaches out
Check fuse F1, next to the input connector. See if it is blown.
I would try probing the test points labeled, VGHC, VGL, VCOM, VCOMF, V12IN1, REF2,3...Last edited by Ken256; 07-07-2013, 11:05 PM.Leave a comment:
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Re: Samsung LE37A556 Screen Fades to white / Bleaches out
Could be something shorted while you were plugging/unplugging the LCD connectors. If you can get it back to its original condition, where the screen would fade to white over minutes, you might be able to diagnose it with a voltmeter. The T-Con board generates or transmits bias and supply voltages. I would suspect some change in the bias voltages over time is causing the fade to white. Put a voltmeter on each voltage rail and see if it changes over time as the symptom worsens.Leave a comment:
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Re: Samsung 2433BW: 2 seconds til black
I've never experienced a bad HV transformer on an inverter board. Rtech may be right.
Another thing to look at is the small value ceramic capacitors that are near the HV outputs. C301 and C302. These caps can go bad. They may appear discolored. They could be shorted, or they start to leak when high voltage is applied. They look good in the photo, but it might be worth replacing them. Its probably cheaper and easier to replace a couple caps than the transformer.
It looks like C301/C302 are connected in parallel with...Leave a comment:
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Re: circuit explanation
This looks like a circuit from a national semiconductor datasheet
It might be fun to build and see how it works.
The LM101 opamp is configured as an inverting integrator. The LM111 is a comparator and produces the square wave from triangle wave.
Basic equation for opamp integrator is Vo = -1/R1C1*int(Vin*dt). Vin is constant for half the cycle, so integration is simple: Vo = t*(-Vin/R1C1), producing a ramping voltage. But this circuit is a little different because a tuning voltage is applied to non-inverting input...Leave a comment:
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Samsung LT23A350 - No signal on Composite Input
Hello. I have a Samsung LT23A350, model LT23A350A250NDY/ZA. The RF and HDMI inputs are working fine. However I can not get a signal on the composite Line-Input. I've tried 4 different known-good sources; video cameras, DVD, VCR. But the TV just won't display a picture from the composite input. I also tried the 3 component Y,PB,PR inputs. Still no picture. The TV simply says "No Signal".
I looked on Samsung's web site for a firmware upgrade, but couldn't find anything. This TV uses a pigtail adapter with 5 RCA plugs. I also probed the continuity on this adapter and it seems... -
NEC LCD1760NX, can it be fixed?
Hello. I have an old 17" LCD monitor here, NEC LCD1760NX, model: L172EN. I was trying to fix it, mostly for fun and experience, but it turned out to be more difficult than I expected.
The monitor will turn on with a fully white screen and then slowly fade to black over a 3-5 minute period. The white screen has some faint vertical lines. Nothing resembling a video signal is seen.
I did not check the electrolytic capacitors directly. Instead, I probed the power supplies with an oscilloscope. The main +5 volt and +15 volt supplies look good, very little ripple.... -
Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)
reneg: It looks like you have been very thorough in your work. The front panel buttons and circuitry is probably good. Hard to say if the RTD2120 is working properly, but in my opinion this type of digital logic chip is unlikely to fail.
I'm guessing there is some major fault somewhere. To narrow this down I would try disconnecting the major circuit assemblies. For example, what happens if you disconnect the LCD panel from the video/logic board. Does it power on and light the backlight? What if you disconnect...Leave a comment:
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Re: Sun 24.1" LCD monitor (Samsung LTM240M2 L02 panel)
I just saw this thread and recognized the Samsung panel LTM240M2. If I remember, this is the same panel in my Dell 2405fpw. I did do a repair on it last summer. Some of it looks similar, but the circuit boards in my Dell are made by BenQ, and were more complex. My dell was having power-on issues, but the backlight would work briefly.
I found that the failure was caused by a surface mount capacitor inside the Samsung panel. These small ceramic capacitors are used to filter the power supply and tend to develop...Leave a comment:
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Re: DIY PSU load tester
Interesting reading, I enjoy seeing other people's projects. I just started prototyping an active load tester. Right now I am using 2N3055 bipolar transistors mounted to old cpu heat sinks. The cpu heat sinks give really good performance when provided with ventilation. I measured a temperature rise of 15 degrees with 90 watts dissipation, so about 0.17 C/W. They just get warm to the touch. I should still have some margin at 90 watts.
I think with my next setup I will try some AOT430 mosfets. They are supposedly rated for 268 watts in a TO-220...Leave a comment:
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Re: HP P2015dn Laser Printer SMPS repair (with Pics)
The K4006 is abbreviated for 2SK4006, a Japanese transistor designation. Fuji Electric N-Channel mosfet: [url]http://www.datasheetdir.com/2SK4006-01L+download[/url]
The other one is more difficult. I figured out the manufacturer from the logo. Its Sanken. See [url]http://www.advanced-tech.com/ic_logos/ic_logos.htm[/url]. Sanken seems to use the TM prefix for triacs. What is the circuit board location for this part? Like Q=transistor D=diode, etc.
Take a picture of the bottom side of the circuit board....Leave a comment:
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Re: need help
From the labels, it looks like the burned component was ZD984, which would be a zener diode. The component looks polarized, because it has a band on one side. The 7.5 could be the zener voltage, and the B could be the tolerance code. Look at the bad solder joint directly to the left of the burned component. If you don't have a service manual, it might be worth tracing out the surrounding circuitry to try and understand it and discover what the root failure was.Leave a comment:
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Improving power supply efficiency?
I have a 1U computer power supply here I was checking out. It is ABLECOM SP423-1S 420 watt supply. The circuit board is labeled FSP500-80BU Rev:1. I was wondering if it is possible to improve the efficiency of power supplies? I measured an input power of 404 W for an output power of 317 W into a resistor load. That works out to 78 %, not terribly bad, but maybe it could be improved? That's still wasting 87 W of power.
I noticed that the primary and PFC transistors seem to be the hottest components after load testing. That's not scientific measurement of power lost, but maybe these... -
Re: Viewsonic VX910
Good job on fixing your monitor. I have a Viewsonic VX710 that has the same power supply and it also had bad electrolytic caps. I've seen some debate on the forums about whether the big primary-side filter cap should be replaced. They do fail. The 100uF, 400V filter cap on my VX710 did fail. When I desoldered it from the board, I found that one of the legs was broken or burned off inside the capacitor case. That seemed extreme.
I also found the power supply controller chip had failed, probably because the main filter cap failed. The controller...Leave a comment:
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Re: Tantalum Capacitors?
Thanks for the replies. I am leaning towards a tantalum replacement. It looks like I would need 10 times the capacitance to get the same ESR, if I replaced them with Al electrolytics. So I would need something like 47uF or 68uF, but would still be cheaper. The Al caps would be bigger though, and wouldn't quite fit the holes/pads. I was thinking of a full recap because it was such a pain to remove the power supply board.
Its interesting what kc8adu wrote about voltage derating, spikes and inrush current. The one that shorted was rated at 50V...Leave a comment:
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