anyone know how to fix a power supply board ?

[joecass]

Sorry if this is outside the scope of videohelp.com forums, most other electronic repair sites want you to pay for advice....
I have this unit called a DTVPAL DVR, mfd by Dish Network (Echostar), it's an OTA (Over the Air) digital TV receiver/recorder.
Actually I have two working units I bought this year which work very well, however back in the springtime I bought a
non-working unit off EBay, wherein the seller said the hard drive was defective and needed to be replaced. Installing a new
drive didn't fix it, and afterward, reading the comprehensive Forum dedicated to this model on AVSForum.com, I realized
this is a common problem with these units, that the early production models were prone to failure, and no repair service was available. I confirmed this by emailing Dish Network, which diganosed the problem as "failure of the power supply board".

OK... so there are two boards inside the unit, one of course is the power supply, the other main board is for all of the
unit's functionality. I am not an electronic tech by any means, but I do know how to use a voltmeter. On this p.s. board,
there is a 8 pin connector which attaches to the main board, with stamped voltages, +12v, +5v +7volt and ground.
When plugged in I checked the pins and it seems none of the voltages are correct..... all are way over spec.

My extremely limited knowledge of electronics leads me to believe this is the reason the unit is non-functional. There is
video output, a boot-up screen, but nothing afterward. The boot up screen shows "Loading Please Wait" and stays
there indefinitely. This problem has been documented and verified by the AVS Forum community, however no one there
seems to believe it can be fixed.....

So my question remains.... how does one determine which components on the p.s. board need replacement ? I've searched high and low on the Internet for replacement power supply boards, it seems they are non-existent. I have called several
TV & electronic repair stores in my area, none are familiar with this unit nor know anything about fixing them.....

[sum_guy]

I am far from an electronics expert, with all the voltages being over spec, typically, you're dealing with a bad resistor on the board, atypically you are on a wild goose chase, or worse, in a printed circuit board, you could be dealing with a tin whisker which renders the whole thing as junk, but only after spending hours testing and diagnosing.

[redwudz]

I would also check the same voltages on the working unit to confirm the PS is the problem. It's surprising the unit appears to boot if the voltages are that far out of spec. All voltages being incorrect is odd, as that would imply more than one voltage regulator is bad. That unit seems to be using dedicated VRs and I don't see any separate IC controllers, unless that device in the upper R is a IC.

If that is a photo of the problem PS, nothing shows as a obvious problem, IE, burned or swelled parts. But a closer inspection may help.

When you measure the voltages, make sure the connectors are plugged in or you may get incorrect readings. You may have to use a modified probe to fit down into the top of the PS connectors. (A unbent paper clip might work)

Other than that, not sure I can help you much.

[misterbill]

How much is "way over spec"? What are the voltages you are reading?

[joecass]

There is one pretty big resistor that shows resistance when no power is applied to the board...... all the
other resistors show zero resistance except this one

The connector just snaps onto the mainboard, nothing is wired or soldered

The connector gives these readings when plugged into an outlet:

12v = 28v
5v = 11v
7v = 15v

When power is applied, the front panel Led's go on briefly..... on a normal working unit, after the Led's go
out, the PAL goes into Standby mode, and the remote must be used to power it back on

There is definitely power going to the hard drive on this broken one, it spins up normally, and a cooling
fan will come on after a certain period of time

BTW, on these circuit boards are printed "designed in the UK 2008" and "assembled in China"

Since both my working units were purchased retail & are under warranty, I don't want to open them
to check the correct voltages...... the first pic I posted was taken from AVS Forum, however my
broken one looks exactly the same, none of the capacitors are blown, no damage that I can see

[edDV]

I'm a sad owner of a dead Mac Mini. All power rectifiers and conditioning are on the motherboard so failure means the whole computer is toast. Mac service shops throw up their hands.

You are at the service of Dish to supply you modular service or a chop shop that recycles DVR parts.

[kimco52]

T

The connector just snaps onto the mainboard, nothing is wired or soldered

The connector gives these readings when plugged into an outlet:

12v = 28v
5v = 11v
7v = 15v

Where are you measuring these voltages? I know you said the connector, but with reference to what? This is a switching power supply. They need to be under a load to measure correctly. With the values you say you measured, I would say your whole unit should be fried if you measured to the correct common point, usually ground.Those values are over 2X what they should be and most electronics cannot sustain voltages that far out of tolerance. I would imagine a well designed circuit should shut down before letting itself get damaged. Chips designed to run at 5V may work at 6V but would blow at 11V.

To say that resistors show no resistance is meaningless. When you read the values on the resistor (You do know color codes, correct?) are they high or low values? What scale are you using with your ohmmeter? Having a volt/ohm meter and measuring without understanding electronics or how resistance in circuits depends on the whole circuit, not just the resistor, when measuring across a resistor may lead to incorrect assumptions.

[redwudz]

If I read the color code correctly for the resistor, it looks like a 23K Ohm, 5 % tolerance. (Red, Orange, Orange, Gold) It may be a bleed resistor for the PS, but just guessing. What I have done is to clip the resistor lead about halfway between it's body and the circuit board, test it, then use a small blob of solder on the cut ends to rejoin it. Lots easier than desoldering it from the circuit board.

That small green device nearby could be a MOV, used like a fuse in case of power surges. They usually blow up if they fail, so easy to tell if they are bad.

Unless you are measuring those voltages with the PS connector plugged into the device circuit board while it's active, they may not be correct.

The apparent IC may be the regulator and the heat sinked devices the switching or power transistors for it. If they are stand alone VRs, they will have a number on the side you can probably look up with an internet search.

[MJA]

guys here helped me fix my Samsung TV tuner with bad caps

http://www.badcaps.net/forum/search.php?searchid=972664

[joecass]

T

The connector just snaps onto the mainboard, nothing is wired or soldered

The connector gives these readings when plugged into an outlet:

12v = 28v
5v = 11v
7v = 15v

Where are you measuring these voltages? I know you said the connector, but with reference to what? This is a switching power supply. They need to be under a load to measure correctly. With the values you say you measured, I would say your whole unit should be fried if you measured to the correct common point, usually ground.Those values are over 2X what they should be and most electronics cannot sustain voltages that far out of tolerance. I would imagine a well designed circuit should shut down before letting itself get damaged. Chips designed to run at 5V may work at 6V but would blow at 11V.

To say that resistors show no resistance is meaningless. When you read the values on the resistor (You do know color codes, correct?) are they high or low values? What scale are you using with your ohmmeter? Having a volt/ohm meter and measuring without understanding electronics or how resistance in circuits depends on the whole circuit, not just the resistor, when measuring across a resistor may lead to incorrect assumptions.

Here's a pic of this connector where I'm measuring voltages..... with the unit fully plugged in and attached to the mainboard.
I never said I understood electronics, back in the prehistoric days of analog tube TV's, I remember fixing a few of them by
replacing resistors..... the voltmeter was first set to 15v DC, flew off the scale, then I set it 60v DC. I'm sure whatever I'm
posting is "meaningless" to someone who's familiar with electronics, if no one is able to scope and fix this unit, what other recourse do I have ? Dish Network stopped selling it and never offered any repair options. However, Sears sold it
for quite a while and offered a replacement warranty. The second working unit I bought was labeled "refurbished", so
obviously someone somewhere is able to diagnose and repair the power supply boards. Also, if there is no
schematic available, what else on this board would you measure ?

[kimco52]

Does that power supply board push down on the mainboard? Are there pins on the mainboard that plugs into the bottom of that connector? Or is there normally a jumper cable from that connector to another similar one on the mainboard? If it pushes down onto pins on the mainboard, then it should be connected when you are measuring the voltages referenced to one of the terminals marked GND. If you are measuring the voltages with the mainboard connected to the power supply, then I would expect to see voltages within range of what it is supposed to be. If they are too high, then the voltage regulator may be the culprit. It(they) probably have manufacturers part numbers rather than the JEDEC numbers.
Except for the 7V, you could probably replace the power supply in there with an old PC supply for the +12 and +5 volts. A small one should be able to handle the current this thing needs. You could get the 7V from the 12V supply with a regulator chip. You could probably use a 7812 and raise the center pin from ground and put a variable resistor to gnd to adjust it to 7V out. That would be a simple and easy thing to do (relatively). There are power supply circuits available for getting the desired voltages. Switching power supplies are buggers. Easiest is to just shotgun the darn things. (Replacement). You could, easily, make a power supply to supply those voltages with a power transformer, and 3 VR IC's, handful of resistors and caps. It would be quiet, also. If you had bench power supplies, you could connect them to the mainboard and see what it does. I have one on my workbench in the garage that has fixed +/-12V, 5V, and variable + and - 0-20V outputs. If the power supply board pushes onto the mainboard, pull it off and use a 16 pin header to push on the pins on the mainboard and use jumpers to connect the power supply to it. There are multiple pins on the header for each voltage and more for ground. They are all the same but using multiple pins to handle the current necessary for operation.

[joecass]

Kimco52: I sincerely thank you for taking the time to respond and for your suggestions, however jury-rigging another
power supply is beyond my capabilites.

Yes this connector just snaps into pins on the mainboard......there are no jumpers. I measured the voltages using the
bottom ground pins, with the unit on, plugged in and operational
There is another computer-type power connector which supplies voltage to the SATA hard drive, that must be
working correctly because the hdd spins up normally

I can barely see numbers on the voltage regulator(s), this will definitely present a problem as to finding exact replacements.
Agreed it would be much easier just to replace the whole damned board, if I knew where to get one.....

The thought has occurred to me that maybe I can find a common electronics shop that would be willing to trace and
replace the apparently defective components, although even then, there's be no guarantee of success

Also, thanks to everyone else who contributed their suggestions !

[aedipuss]

Kimco52: I sincerely thank you for taking the time to respond and for your suggestions, however jury-rigging another
power supply is beyond my capabilites.

if you can't do that then most certainly you can't repair the original either. just toss it and look for a working replacement, you're wasting people's time.

[sum_guy]

Just found this... Channel Master CM-7000PAL is the identical product to the Echostar/Dishnetwork device. So... if you can find out who can service the channel master, or get a power supply from one. You are fixed up.

http://news.cnet.com/8301-17938_105-20011472-1.html

[kimco52]

Kimco52: I sincerely thank you for taking the time to respond and for your suggestions, however jury-rigging another
power supply is beyond my capabilites.


The thought has occurred to me that maybe I can find a common electronics shop that would be willing to trace and
replace the apparently defective components, although even then, there's be no guarantee of success

Also, thanks to everyone else who contributed their suggestions !

Well, Good luck. We tried. Sometimes you just gotta know when it is time cash in and cut your losses. It would be nice to verify if it was the P.S. or not. But, if it can't be done,..........

[sum_guy]

Joe, you certainly didn't waste my time, I like a challenge. This one was a new one, which intrigued me even more, best of luck to you.

[bendixG15]

The calendar is against fixing things, today its a throw away world, no more fixit shops..........

[sum_guy]

My local fix it shop is run by a real pain in the azz, this guy is so infernal it's ridiculous, but he never quits, rarely gives up, and there is almost nothing he won't tackle. The shop is in my spare room in my house and I hate when I go in there because it reminds me of everything in the first sentence.

[zuckuss483]

I am a power supply engineer. It seems to me that the output voltages regulators are blown and you are just get unregulated dc out of your PSU. I am surprised your electronics are still working if your reading these high voltages, you may have also damaged input sections of the device its powering which may need to be replaced and checked out(requires schematic). The problem is diffidently in the secondary side (output section, top of unit anything above double black line written on the board) of PSU. My first suggestion is to just replace the psu as parts that may need to be replaced may be hard to get. Ok first thing I would replace any thing with the reference designator (U# or IC# or D#) towards the output connector. Also look for anything burnt or black. The resistor with very low impedance is the current sensor on the primary side and it should be very small that a standard meter could not measure it. Make sure all other resistors do not read short (0 ohms) I would also recommend not measuring resistance while the unit is on.

[charlesr]

I am new at this forum and am feeling my way around to post what I have learned the hard way. I'm an old retired accoutant and know nothing about electronics. So, here goes.
I have two ChannelMaster CM-7000PAL Over The Air units that went bad just before the warranty expired. ChannelMaster swapped out at least 5 before I got a one that worked. One time they sent me a unit which was all beat up and the batteries in the remote was all green with corrosion. Then I knew there must have been a real big problem with these. I carried a unit to several TV repair shops and none would accommodate me. So, I started looking on the internet for a DYI tutorial. Long story, I finally figured out how to fix mine. Located somewhere here in an earlier post is an excellent photo of the inside boards. Well, the brown board on the left is the power board. On the right would be the disc drive which has been removed. (Before you begin to disassemble your unit, take a piece paper and pencil and sketch out what you see in your unit. Believe me, I forget and that scrap of paper helped me to re-assemble the unit.) From other tidbits of info I received on YouTube, etc. I figured out since the unit would not boot up, it must be a power problem. So, I removed the brown power board, drew out on my piece of paper where the capacitors (they look like small cans and referred to as Caps) by number were located. Each are identified by C1, C2, etc. Sketch where these are located on your piece of paper. All you need to know is two identifying pieces of info on each capacitor. For example, 14v & 2200uF. This means the capacitor requires 14 volts and 2200 micro farads. I think my board had eleven capacitors that I replaced. The capacitors are very cheap. I ordered mine on eBay not knowing that I had a local electronics store that had everything I needed. Don't go to Radio Shack as they require you to order them at their online store. I saw a YouTube video on how to remove and replace the Caps. I used a skinny soldering iron that looks like a long screwdriver with a pencil point. After re-assembly, both units worked great.

[MJA]

I learned one thing about CAPS.never buy the cheapo ones .one Panasonic . generic ones will not last.

The guys at http://www.badcaps.net helped me a lot to fix my Samsung DTB-H260F tuner box

[Megahurts]

A switch mode power supply requires feedback from the secondary to the primary to regulate properly. This is done by monitoring one of the secondary output voltages and fed to an opto-coupler (the 4 legged device half shown under the red cable) back to the primary. This will be regulated with or without a load.

Since all your voltages are about doubled, it looks like there is no feedback and the primary is running at max. The monitoring circuit usually uses transistors, zenier diodes and resistors all surface mounted on the bottom of the board. Without a schematic, it would be hard to trouble shoot.

With a variac (variable ac supply) you may be able to lower the ac voltage where the output voltages are normal and see if the unit works. If so, then look for a used power supply.