Coolsat 8000 power supply problem

[rrob311]

My Coolsat 8000 decided to quit. I checked the power supply and I only have like 2/3 of the voltage that is listed on each output of the supply. Does anyone have any ideas of what could be bad on this? It looks pretty simple but I do not understand circuitboards very much. How can I go about testing the components?

 

[olegray]

rrob, I had a simular problem with a CS8000, only I didn't have any output voltage. Looking at mine with the ocilloscope, I pinned it down to the FairChild Power Switch(FPS) 5L0565R, which is a four pin semiconductor mounted to a heatsink. That baby is pretty pricey, and the only place I could find one was in England for around $25.00. Now, if you have 2/3 of the voltage at each output, hopefully you are just looking at a bad capacitor, diode or resistor. You might measure voltage in the large diode area beside the flyback transformer and see what you get on each side of those diodes. Sorta look for capacitors and resistors that are bulging. I think the trouble with the one I have was caused by not having enough ventilation inside the unit, so I put in a small 12v, 0.01A, 40mm brushless fan between the power supply and main board pulling air in over PS and out over MB. Hope this helps. Ed

 

[rrob311]

Here are some pictures. The grey diode boxes at c1 and c2 have roughly 11.5vdc going through them.

 

[migold]

rrob311;
Typically, in a switch-mode power supply like this, you will have marginal voltages when the values of the capacitors decrease below a nominal value. From your photos, nothing appears to be abnormal for overheating or bulging, at least as far as I can see. My best guess is that the capacitors have decreased in value, which is normal as they age, and now they have decreased below the value that is required to provide you with enough voltage to properly run your circuits. Probably not all your capacitors are bad, but it will be difficult for you to detemine which are bad without proper test equipment. The capacitors are the stand up parts with the stripe down one side to indicate the negative polarity lead. I would guess that the most likely candidates would be the ones on the 5 or 3.3 volt supply lines near the connector in your photo #1. I would replace the ones with the highest ufd values first, replacement is the easiest and most reliable way to ensure that you get rid of the bad part. It would not hurt to replace all of them on that end of the board. It is HIGHLY NOT LIKELY that the large one on the far end of the board is bad, so go with the low voltage ones first.
Good Luck.

 

[rrob311]

So if I remove them from the board are they easy to test? I suppose I could just start ordering them if they are inexpensive. My meter has a spot to put something in. It says Diode/Ohms/Cap.

 

[olegray]

rrob, before you take the PS board out, looking at picture #3, the diodes just to the left of the yellow transformer. See what the voltage is at each one . Measure one side to ground, then the other side and see if these voltages are lower than normal. Ed.

 

[rrob311]

Would normal voltage be listed on the part being tested?

 

[olegray]

Looking at picture #3 of the diodes on left of the yellow transformer, here's the voltages that I read. The two larger diodes reading from left terminals to ground is approx 4 volts on each. Move on up to the three smaller diodes above that, reading from the left terminals to ground, 12 v, 7 v and 23 v in that order. Ed

 

[migold]

You may try to test, but in my experience, a marginally good/bad capacitor will not always indicate its condition accurately on a tester. They are not expensive, and it is better to go ahead and replace them to prevent future problems. Given enough time, they will all fail. Voltages on the capacitors are the max voltage rating, and they are usually run at 30%-60% of rated max voltage.

 

[rrob311]

Looking at picture #3 of the diodes on left of the yellow transformer, here's the voltages that I read. The two larger diodes reading from left terminals to ground is approx 4 volts on each. Move on up to the three smaller diodes above that, reading from the left terminals to ground, 12 v, 7 v and 23 v in that order. Ed

bottom larger diodes at just under 2v dc. Next one up is 3vdc. Next up is about 2.5vdc and the top one is 6.8vdc

 

[olegray]

It looks like your problems are on the right hand side of the yellow transformer. I would replace the larger stand up capacitors on the right hand side and pay attention to their polarity (the white stripe). If that doesn't do it, you would really need an oscilloscope to see the switching voltage of the 5L0565R FPS. Does your receiver have a fan installed in it? If not, when you get it up and running, it would sure be insurance to install one. I sure believe excessive heat was what took mine out. Ed

 

[rrob311]

Ya I have an oscilloscope, It has a smaller screen but it was an expensive model so I hope it would measure what I need. The receiver has a fan but it is pointed towards the tuners so I think it could use another one. I first had problems with it last summer when it was hot out and I cleaned the dust off the board and kept it ventilated and it quit cutting out. Now that FPS part that you mention what does it look like? I will try to hunt down leads for the scope. I don't have a manual for it and when I bought it 10 years ago I never really toyed with it.

 

[olegray]

The FPS 5L0565R is located down to the right of the yellow transformer in picture #3. It is a black, flat design semiconductor with four leads, mounted to a metal heat sink with a screw. It has 5L0565R stamped on it. I bought one from Littlediode Ltd., United Kingdom. I think they are listed on ebay also. If you use a solder sucker on removing those components it will make life easier and save the PCB from excessive heat. Ed

 

[rrob311]

Cool. So how do you check this with a scope? Is there an article anywhere that simplifies this?

 

[olegray]

Here is looking at pin D on the 5L0565R, the output of the device. Not the best in picture. There are actually harmonics between the top and bottom waveforms that do not show in the picture too well. I was using an attentuated probe. Good luck in hunting. Ed

 

[rrob311]

so it should have a waveform like that with it just powered on?

 

[olegray]

Yes, just turned on not connected to lnb. The picture was taken just sitting on dinning table. Ed

 

[rrob311]

OK I found my scope. I forgot I have a lead for it. It is an elenco s-3000a. I never had a manual for it so I am not sure what settings to use. If you could give me volt/time settings for it and ac or dc i can try to get a reading.

 

[olegray]

Input to DC. Volts/CM to 10-20. Sweep Time/CM to 2ms. ....This should get you in the ball park. You may have to adjust the varaibles a bit.. ground the scope to the receiver metal case. Ed.

 

[rrob311]

there is a lead off of the probe. Is that the ground?