fta Sat TV decoder: Need some ID

[bushtech]

Busy working on my fta Sat TV decoder. But I have come across some things that I can't identify.



In the small red rectangle is two legged smd alfa 010. What is that?

Then the big red rectangle has got something that looks like a 4 poster carport roof. It has got 4 leads coming up from the pcb and pushing on the underside of the carport. Would like to know what that is.

Then there are a whole lot of smd components with strange names like:

CA
CF
CU
CP
CV
CM
LRF
LU
LP
UP
RP
RU
RF
RV
L

Do they denote different smd components or are they just showing different power lines. If they are different components what are they?

Thanks for the help (and furthering my education)

 

[73's de Edd]

Small red box is ferrite based 10 uh choke . . .working on yer car port . . . to see whether there is a motoring cycle or a Mercedes Bents under it .
Already accounted for the tuner and modulator and the porcupine cooled MAIN U/P of the system .

Up near the 4 RCA connectors is being the units wall wart power .supply input.
You might take a Blue mini Sharpie and circle the botom pads of all of the 14 electolytics of the unit and power up and see which ones have a voltage presence across them.
I see one 3 term regulator near the main U/P and the nearby Q301 might be related to doing a regulation function also.
Plug in and see how many of those E-caps have voltage across them.
What brand is this unit ?


73s de Edd

 

[bushtech]

lol. Thanks St. Edd

How do you figure out it's a choke?

 

[73's de Edd]

See its companion . . . . . over at the left side of the modulator.

 

[davenn]

See its companion . . . . . over at the left side of the modulator.

that doesn't answer his Q !!

I have actually seen SMD fuses in that style

Then there are a whole lot of smd components with strange names like:

CA
CF
CU
CP
CV
CM
LRF
LU
LP
UP
RP
RU
RF
RV
L

are those letters on the board or on top of the component ?
if on top of the component .... transistor or IC, then it is a type number
finding the correct SMD code can be difficult as there are often many components that use the same code


Dave

 

[bushtech]

Thanks davenn. Those are suffixes on the board

 

[davenn]

Thanks davenn. Those are suffixes on the board

I had to squint really hard to see some of them

they seem to use C, CA and CP for capacitors ... why ? I don't know
CE for electrolytic capacitors

I see R and RP for resistors

L and LP for inductors

Q = transistors
Y = Crystal
U = IC's


That thing you labelled in the small red box is LRF ... it may well be an inductor as Edd suggested
without a clearer view, I am not going to jump to that conclusion knowing the fuses I have seen in the same style


are some of the ones I could pick out

 

[bushtech]

Thanks a mil dave. Unfortunately I am as bad at photography as I am at electronics

I suppose when you know your onions you can read a circuit board like a book. Unfortunately it's all braille to me. Don't know if I'll ever reach that level of proficiency.

Another thing that interested me on this board is the finned heatsink. That is glued onto the ic that it is cooling. Very glad I don't have to scratch around there

 

[bushtech]

Apologies edd. Only saw the second part of your post now.
What brand is this unit ? http://www.spacetv.co.za/pages/our-products/dsd200-hd-4346.php

 

[bushtech]

3 of the caps show no voltage across them, I am picking up replacements tomorrow for all the caps. Hope that sorts it

 

[davenn]

Another thing that interested me on this board is the finned heatsink. That is glued onto the ic that it is cooling

yeah, that is often seen in these types of devices (sat receivers, DVD players etc)
you will sometimes see smaller IC's and heatsinks than that too, only 2 or 3 fins

3 of the caps show no voltage across them, I am picking up replacements tomorrow for all the caps. Hope that sorts it

that doesn't infer a faulty cap, rather more likely a PSU problem where there is no power getting to those caps

make sure there is power coming into the unit at that power socket ... top right to the right of the RCA sockets ... you may have a faulty plugpack

electrolytic capacitors usually fail by drying out ... this causes a reduction in their capacitance value
say, a 1000uF may only be a couple of 100 uF that sort of thing

they don't cause a loss of voltage across them

 

[davenn]

a few edits in that last post ... hope you caught them all

 

[bushtech]

Hmmmm. Now you're starting to worry me.

It's a 12v 1.5A out power supply but I only read around 3v on the power supply plug in connector. Did plug in another power supply but got the 3v again. In my ignorance reasoned that something on the board is dragging the voltage down.

 

[davenn]

It's a 12v 1.5A out power supply but I only read around 3v on the power supply plug in connector. Did plug in another power supply but got the 3v again

OK so I'm assuming both PSU's are testing correct voltage when unplugged from sat unit ?

that would infer as you suggested ......

In my ignorance reasoned that something on the board is dragging the voltage down.

but unlikely the electros ... more likely a transistor, diode or IC


As I said in a recent thread to some one else, these things are not designed to be repaired, you will be unlikely/lucky to find a schematic for it

 

[bushtech]

Thanks for the heads up on the edit, read it now. I have also ordered diodes D751 and D752 for replacement, couldn't find D754 (see it at LH corner of carport)

Yeah, was planning on just replacing it, phoned Space and was told that they are not importing them anymore. The interesting is that you could always get 2 decoders from 2 different suppliers. However the Space one allowed you to tune to other transponders on SES5 satellite whereas the only decoder now available in SA is not tuneable. Apparently the secondhand tuners from Space have just shot up in value.

So this will now be fixed if possible

 

[bushtech]

Yes both supplies read correctly when unplugged from unit

 

[73's de Edd]

Does that wall wart specify if its putting out DC or raw A.C. ?

THE GREAT INDUCTOR FIASCO AND BROUGH-HA-HA . . .

I just NEVER have happened to have seen an Alpha electronics choke . . .marked . . . 10 microhenries . . . guising itself as a fuse.

Bush . . . Whup out 'yer ohmmeter and switch to its ohms function and not diode test mode , then short your leads to see your reading produced, and then, with no power applied to unit, test either inductor and see just how very close to 0 ohms that they're testing.

I would ask for a close-up photo of the other side of the board but I'm expecting it to basically to be a total groundplane with only massive SPECIFIC circuit " islands " being exposed.
With the wall wart unplugged, can you use your ohmmeter across the power input connector and just see how low of a resistance you are reading, try it with both meter lead polarities .
In that " power supply corner " I am seeing two hefty little inductors that could be related to buck converters for acquiring 5 volt and 3.3 volt logic supplies from the two 8 pin SMD i.c.s, but I see no associative power semi conductors.
What semi devices are you seeing under the " car port " . . . . if any ?
Until I got your model number I thought that might be a connective plug area for receiving a side inserted, credit card sized, plastic SMART card with its offset onboard ROM that uses 13 GOLD flashed contacts for connections within the units plug?
Also, since the input 12VDC voltage is being pulled down to 3V you might ohm out from power bus in at that power connector to ground and see what low resistance exists there.
To pull down 12V to 3v at 2 amps would be suggestive of a 5 ohm or so short being present Then you trail down interconnects that branch off that buss and temporarily shed them to see what is bad and pulling that voltage down. Bad diodes ? shorted electrolytics ? power semiconductors ?

73's de Edd

.

 

[the great potato]

nice to see another guy with a FTA system, just wanted to add in you can get a decent FTA box on ebay for like 26 bucks. there not great but it works for sure. What sat you pointed at ? Im at galaxy 19. But wondering if theres better out there...

 

[bushtech]

O great potato

I am in South Africa using SES5 sat, don't think it will be of much use to you

 

[bushtech]

Wall wart putting out 12DC at 1.5A
Multimeter in lowest Ω mode (200Ω) i get a reading of 0.2Ω when touching probes together.

Measuring the two inductors:
PH01: 8.1Ω
PH02: 5.8Ω
And Edd, a brilliant deduction on the car port. It is a credit card slot. Decoder doesn't use a credit card and it's hidden behind a door so I had long ago forgotten about it.

Under the carport are some components including a 30 pin chip.

News on the decoder: Replaced some suspect caps and suddenly saw 12V on the power supply. Thought I had got lucky, plugged it in and it started working, worked for about half an hour and bombed out again with 2 flashing red lights

So will start checking as per your last paragraph