CDTV : Sound Problem (One channel saturated)

[gibs]

Hello guyz,

I just bought a CDTV, I like it a lot.
It own the CD Kick (Kickstart 1.3, 3.1 and the Original CDTV), and the elbox CDTV/2 (2mo of fast Memory).

Therefore I got a problem with it. I channel is saturated.
I had a look on the MB and didn't noticed Capacitor failure or something damaged (Caps on CDTV are SMD).

So I would like to know if someone can guide me to identifiate the problem, because I really want to fix it.

Thanks.

[Loedown]

If you have an oscilloscope, you need to go around U5 and U6 to find where the signal is going awry.

Most likely one of the chips has failed, in worst case, replace both and it should be all good, they're not expensive. In rarer cases one of the discrete components has failed, but still more likely the TL084.

[gibs]

Thanks for the help, I have already ordered 2 LF347N on monday.

Here are my mesurements when the CDTV is not producing sound : http://dl.dropbox.com/u/1566495/Amiga/cdtv.jpeg
I forgot to say that +12v -12v is ok.

(on the Amiga 4000 repair service I can't see 6v...)
http://amiga.serveftp.net/images/Aud...atic-large.jpg

[Loedown]

I was quoting from my schematics which have the TL084 as the output IC.

Those 6V levels look suspicious.

[gibs]

I guess you own a CDTV...Which revision ?
Mine is a 2.2.1

I'm not an electronic genious, but if those 6v are suspicious, the problem should be in the four 22uF capacitors (C11,C12,C20,C21) or resistors (R18,R28) (sheet 4 of 12 of the CDTV Schematic (http://www.ianstedman.co.uk/download...schematics.zip) as I have 2,5v as output of my four operational amplifiers from the 1st IC.

Am I right ?

Could you eventually do some mesurements to know what is the correct voltage ?

[Loedown]

I just have the schematic, I don't own a unit.

[Shadowfire]

Based on your measurements, either U5 or Paula (U4) is at fault. And it's probably Paula. If you have another socketed Paula in another machine, swap them out before putting a soldering iron to your motherboard.

Etiology: Note that both inputs of U5 (pin 9,10) are identical, only the output is off by .1 V. This indicates that the opamp may be OK, and that the input from Paula is probably low. Keep in mind that the opamp could be on its way out, but when an opamp fails it typically swings out to either voltage rail, which isn't happening here.

The 6V readings on U6 are for opamps used as voltage followers in the CD audio section, and appear to be working correctly.

[gibs]

@Shadowfire : Thank you very much for your help. You're right, the Audio output on CD is ok.

I have an A600, A1200, CD32 unfortnately none of them have Paula socketed...more than this, it's not the same format
I think I can find the same on a A500+ from what I've seen of google Image, which other Amiga computer can I find Paula socketed ?

Again thank you !!

Edit : I have ordered a brand new Paula chip on eBay. I'll keep you informed about the swap...

[Loedown]

An oscilloscope is a better prospect, you wouldn't be guessing.

[Shadowfire]

Yes. Unfortunately an oscilloscope is far more expensive than buying another paula & U5.

CD Audio gets mixed in right before the mute circuitry, which is after the Paula -> U5 -> U6 "Amiga" audio circuitry.

[Loedown]

Originally Posted by Shadowfire

Yes. Unfortunately an oscilloscope is far more expensive than buying another paula & U5.

CD Audio gets mixed in right before the mute circuitry, which is after the Paula -> U5 -> U6 "Amiga" audio circuitry.

Without owning one, I took an educated guess, guess I need to be re-educated

[rkauer]

Originally Posted by gibs

<SNIP>
I think I can find the same on a A500+ from what I've seen of google Image, which other Amiga computer can I find Paula socketed?

<2x SNIP>

A500, A1000, A2000 and A3000.

[gibs]

Hi back there.

I have changed Paula, and same problem

[Shadowfire]

You never mentioned which channel is saturated. I'm assuming the right channel? At this point repair work is needed. Without an oscilloscope, I would recommend changing the parts (in this order):

C20/C21 (right channel) or C11/C12 (left channel)
U5
U6

[gibs]

Hi Shadowfire,

Both are saturated.

1st I thought it was 1 channel because of the Amiga "Stereo". the channel were was the bass/drum were saturated.

I have changed U5 (LF347N) , that I put in a socket. The sound is still saturated.

Here is a sample : http://bit.ly/b3wqZL

I confirm, that the sound isn't saturated when I play CDA tracks. For example, when I start XENON 2, the sound is pretty good (on the intro) and it is more that 4 x lower than when then sound come from Paula (as I have other console on my amp, the cda volume is correct). So maybe it's not needed to change U6 ?

[Shadowfire]

I don't know what an .m4a audio file is - any reason it couldn't be ripped to something that plays universally, like an .mp3 or .wav?

The only things in common with both channels are the low pass filter and the mute circuitry. The mute circuitry would also affect the CD output, though.

Pins 6 & 11 of U5 & U6 are +12V/-12V respectively, are they not? At this point I would (for lack of any other diagnostic tools) replace C20 and C11, the 22uf electrolytic capacitors.

[gibs]

Yes, on my third message I said +12 & -12 were ok on U5 & U6.
Ok going to change those caps. I'll keep you informed.

Ps : M4a is the audio of MP4. I think you can play it with Mplayer (if you own MorphOS)
Therefore here is the mp3 http://bit.ly/bF5dDZ
and a big pic (useless) : http://bit.ly/d7zKR9

[Loedown]

You only replaced one op amp????????

[gibs]

Originally Posted by Loedown

You only replaced one op amp????????

As shadowfire said, U6 is used for the Cda.
So I only changed U5. (not easy to unsolder)

[gibs]

I have removed C11 and C20.Then I have measured them. they value are 22,8 uF & 23 uF. so I guess they are not faulty. Therefore I haven't replaced them yet...