Lost sound on a modified PAL Sony

[Lurker]

This might be an interesting problem..... probably going to have to solve it with a Tivo HD if I am one of the lucky 5

Sound would drop out when recording. Sometimes changing the channels would bring it back.

So far have followed advice and swapped the Hard drive and the power supply (from a spare Philips unit) to no avail.

I think a PAL modification - specifically the stereo mod has come un glued (well unsoldered) and I dont know where the wires reattach.

The interesting thing is it appears to be a NICAM mod that doesnt follow any of the guides. It is a proper circuit board in a plastic box with "Andrew Payne NiCAM Decoder" on it. Anyone recognise it?

I will try to upload photos but the wires run from the 2 capacitors on the sound chip back to this unit into L & R labelled soldered connections. There appears to be a wire from (I think) -5v loose on that circuit board and I cannot tell where from. Hard to tell as there is a few terminated witres that seem to go nowhere - possibly from earlier mods.

The tuner is a TMDG2-505A and there appears to be no wire from pin 21 that I can see. There is a long wire from the circuit board with label "SIF" or "SIP" which I guess might be the sound input but I cannot see any evidence if soldering to show where it was originally - again pin 21 shows no evidence of a soldered joint.

I cant just use the Philips box as I have no source box to use.

Help....

Chris

[Lurker]

Photo attached

Wire on right is the long one that may be sound input

[Darren King]

The interesting thing is it appears to be a NICAM mod that doesnt follow any of the guides. It is a proper circuit board in a plastic box with "Andrew Payne NiCAM Decoder" on it. Anyone recognise it?

Sorry, never heard of this person or seen the mod. Can't find anything under Google either.

There appears to be a wire from (I think) -5v loose on that circuit board and I cannot tell where from. Hard to tell as there is a few terminated wires that seem to go nowhere - possibly from earlier mods.

That's the problem when people experiment but don't clean up or document any changes and then expect other people to be mind readers That aside, where does the other end of this wire attach on the TiVo motherboard? This might provide a clue for me to tell you what its purpose is.

The tuner is a TMDG2-505A and there appears to be no wire from pin 21 that I can see.

There won't be one. Pin 21 is decoded baseband mono audio output that can be fed straight into the two capacitors on the micronas chip (ie the mono sound modification guide). You can easily just do this if you want to bypass the unknown stereo decoder and just have mono sound.

There is a long wire from the circuit board with label "SIF" or "SIP" which I guess might be the sound input but I cannot see any evidence if soldering to show where it was originally - again pin 21 shows no evidence of a soldered joint.

It will be SIF (short for Sound Intermediate Frequency). The take-off point for this is shown on the Mark 1 Stereo modification guide, which can mean either Pin 22 of the tuner, L28 or Q14. It is the same take-off points regardless of either NZ NICAM or AUS A2 sound standard.

I guess a good start would be to take a photo of the decoder board and if possible a shot of the decoder chip on the board and from there I may be able to piece something together.

Failing that Skolink might be able to give a hand too. Post what you can here so we can all help out.

[Darren King]

That's a damn fine shot! Really good capturing the PCB pattern.

Well, for starters a head count of the wires shows nothing out of the ordinary. I can deduce as follows:

The shielded grey wire with the red/white inner wires is the sound output to the capacitors on the Micronas.

The shielded braid of this wire is covered in black heatshrink. Does that single red wire also attach to the same point? Hard to tell as I can see a partially obscured termination pin and cannot see if the red wire goes to the same point as the audio braid or the pin next to it.

I would say the blue/white striped wire next to this is your 5V supply. I say this as I can trace the PCB pattern in the photo and the trace goes around to the yellow indicator LED and also goes to several other places via links and such.

You are correct the wire you have called SIF would be indeed that by the looks of the parts configuration around where it terminates on the PCB.

The only other puzzling thing is that wire you have called -5V. I say this as there is no -5V line in a TiVo (in fact there is no negative lines at all - there's only 3.3V, 5V, 12V and 32V) and this is the only wire I cannot account for. Could you clarify what the big chip is? From this I can tell you what the wire is possibly for.

[Lurker]

The long wire is in the circuit board in the location marked SIF (top left of photo)

It does look like the SIF pickup point near Q14 is the right place - I can see some very faint evidence of sodering but if i press the wire to that I get no sound. Would the sound come back or at least crackle - or does the sound module fall over and stay fallen over until a reboot?

The wire I think is the -5V DC is soldered into the spare HDD connector (the wires go red, black, black, yellow - and it is in the first black)

Will try to get a better photo of the underside of the circuit board

[Lurker]

...oh hang on - more to answer

[DOlsen]

No need to fix with a new tivo, should be easy to fix. Details about what is required is on this site here

Power is +5V and +12V, not -5V

[Darren King]

Found what we might be looking for here:

http://forums.oztivo.net/showthread.php?t=1458

I know somewhere in the memory bank I had come across a decoder being built. What threw me is the name. All sorted now and repair should be a breeze!

Edit: Thanks DOlsen. Beat me to it

[Lurker]

Wow - great

Looks like the long wire is to the SIF point but I am struggling to find where the wire from the black power cable goes on the circuit board

Wonder if it redundant?

3 power wires are soldered into the connector from the PSU

Red - goes to +5v
1st black wire - but connects to nothing
2nd black - no soldered wire
yellow - goes to +12v DC

any other power input - looking at the schematic but struggling a bit. Cant see why someone would solder in a wire and then not use it.

[DOlsen]

3 power wires.
Gnd
+5V
+12V

So, you need to reconnect the gnd wire at the decoder board, and, reconnect the sif input on the main board, and, should be good.