Echostar AD3000IP Viaccess - Audio problem

[davjen]

I have decided after more than a year to do something about sorting out the audio problem. I removed the old IC and discovered that the pads under pins 59,60 & 61 on the CXA2078Q had become detached from the board. I sent a picture of the problem to Michael Danfield and he thinks that these pins may be not used - I also cannot see any connection under the pads. Llew has been very helpful in the past with the parts list for this model as I also need to replace R3 on PSU and possibly change capacitors, C10 & C11 which are looking blown, however, the type fitted are 470uF, 200V. Are you able to advise on whether the pins form part of the circuit and any other advice you may have.

 

[Llew]

Pins 59 > 61 are audio input 5 L/R, unused in the Echostar.

Best to replace the electrolytics with the same value. Must have have been changed during the production run.

 

[davjen]

I was hoping that all would be well after fitting the new chip, however that was not the case. On turning on, channel no. was displayed on the receiver but nothing on the TV. Pressing "menu" - nothing happened. Output from PSU seemed OK, voltages slightly down. Any suggestions - refer to Michael Danfield?

Thanks to Llew for all his help,

Dave

 

[Llew]

Pressing Menu doesn't show anything on the receiver display anyway. You've lost video/audio output from the chip. Only thing you can do is check your chip pin connections for shorts/ no contact with the pin pads.

 

[davjen]

Thanks for your help Llew, the receiver is now working again but the original problem is still there, ie no audio on left channel. I have still to check that all else is OK. Is there some other means of following the trail of the audio?

 

[Llew]

Good that you have apparently successfully replaced the chip. Not a job I would want to try

It might be easier now to trace the fault, having taken the chip out of consideration (he said hopefully).

I'll look further into it when I get a little time.

 

[davjen]

Llew, hi

Just to give you an update - I have now done all other checks on the system and found that all is well so far other than the audio problem. I have also in the meanwhile replaced the C10 & C11, important that they are max 22mm dia and no longer than 40mm. Looking at the R3, I think I would probably have gone for a 3W, 15K, metal oxide film instead of 2W, which would fit and being beefier would dissipate heat better.
Hopefully you may be able to help on the audio.

Thanks for coming back.

Dave

 

[Llew]

Ok, will have a check today on the best way to trace the audio path if you have no access to test equipment.

 

[Llew]

OK the easiest way to check the audio would be to use a PC speaker and its amplifier, you could borrow one from your PC for the duration.

You'll need to fashion some kind of probe to connect to the speaker's audio lead. My lead terminates in the usual 3.5mm stereo plug. A thick wire soldered to the tip terminal of a 3.5mm chassis socket will do for the probe, and a wire with an alligator clip for connecting to the receiver's chassis can be soldered to the ground terminal of the socket.
Tape it up so the socket doesn't come into contact with the components of the receiver while you're testing.

You need to trace back through the LH audio path from the TV scart (pin 3), through the CXA switch chip, to the encoder.

Switch your receiver on to a channel, with the PC speaker on, and probe pin 3 of the TV Scart. If no sound, go on R647 (to the right of the Scart block).

If no sound, go to pin 49 of the CXA chip. This is the LH audio out to the TV scart. If no sound, go to the LH audio input pin of the chip (pin 1) and let us know if you have any audio there.

 

[davjen]

Thanks for coming back to me.

It may take me a few days to sort out the connections etc. The difficulty maybe to rig it up in order to be able access the connections inside but I am sure I can sort something out.

Let you know how I get on.

 

[davjen]

If I use my PC amp & speaker, which is no problem, as you said, it would have a 3.5mm stereo plug to fit the PC's onboard audio, I am not clear why you would need the amp in this situation. Wouldn't there be sufficient output for a speaker to respond when there is a signal present in the powered-up satellite receiver?

 

[Llew]

Sorry for the confusion. I meant using your speaker's internal amp to amplify the Echostar's line level audio. You could do it through the PC's audio card; I just thought it would be more convenient to detach one of your speakers from the PC and use that without involving your PC.

 

[Llew]

Something like this that I made would do. An old sewing needle would be fine for the probe. You can blunt the tip a little so you don't prick yourself!

 

[davjen]

I have just completed the tests as per your advice - quite interesting and confusing results came up. As expected, no sound at all at pin 3 of the scart socket. At R647, I got noise on the side closest to the CXA chip, the same applied to Pin 49. From pin 1, I got proper audio.
This confuses me as it sounds like the chip is at fault again as there is audio in at pin 1 from the encoder and no corresponding audio out to pin 49.
It will be interesting to hear your comments on this one.
By the way, I made my probe using the 1.25mm, centre copper core from CT125 cable which I sharpened the one end to a point, used heatshrink for the whole length except for about 3mm of tip, using small twin core cable with small insulated crocodile clip on other leg and the 3.5mm socket on the other end, heatshrinking all exposed metal.

 

[Llew]

Well it seems we can possibly rule out the actual switch chip as you have the same results after replacement. Also anything back from the encoder chip. Maybe the components assosiated with the chip or the switching process , although I assumed the L/R audio is 'ganged' as with a physical switch.

I'll delve a bit more into the circuitry (as much as I understand it!) and post back.

 

[Llew]

Rule out R647 - not part of the path we're interested in. My error. Pin 49 of the chip goes to the series network CE625 and R625, which terminates onto pin 3 of the TV Scart. These are the only components on pin 49. They reside about half an inch down from the left-hand edge of the Scart screening box. They're unlikely to be the culprit, as there's no path to earth that might cause a short on pin 49.
To be certain, would you let me know the voltage you have on pin 49 - it should be ~4.5V.

 

[davjen]

I only now got a chance to have a look at the connections from Pin 49. Can you confirm that the series network is R625 & CE625. It looks like the ones you say on mine are R626 & CE625, the other ones, R625 & CE626 are in line with the audio phono sockets. I will check the voltage at Pin 49 tomorrow and let you know.

 

[Llew]

Probably R626, yes. Certainly CE625. The spare board I looked at has smudged printing around that area. So does another one I have. Whatever, you can see the copper print coming out from CE625 to its resistor.

 

[davjen]

Sorry to give you the run around on this one, Llew. Checked the voltage on Pin 49 - 4.49V. I also did further checking- R626 to pin 3 on scart showed connected. R626 has identifier as "621" which I assume would be something around the 600ohm, I checked mine and it was 619ohm.
I still need to do your first check with the probe again with R626 instead of R647, that I will do tomorrow. I also checked my Pin 49 to pad connection just to be sure - OK there.

 

[Llew]

I did suspect there might somehow be a problem with the I²C data bus lines to the CX chip, which controls the volume and mute of the left and right audio, but looking at the circuit for the chip, there's no means by which they can seperately adjust each output. This is obvious really, as you wouldn't normally do such a thing anyway. So I think we can forget that area.

Work still to be done I'm thinking.