cd liest, zeigt laufzeit, aber kein ton am ausgang

[cpucomp]

ciao revox-spezialisten
mein b 225 funktioniert alles wie gewünscht, er liest cd, spielt sie auch ab.
am Ausgang kommt aber leider kein Signal, tote Hose.
Sicherungen sind überprüft und ok.
wo soll ich mit der Suche beginnen?

Gruss und Danke für Hinweise

Ueli

[MilanMilosevic]

Re: cd liest, zeigt laufzeit, aber kein ton am ausgang

Hello,

check the followng:

1. Does the output relay click when you turn the player on?
2. Is there audio signal reaching the inputs of the relay?
3. Does the signal reach the inputs of output op amps?
4. Is there signal at the outputs of DAC?

Basically, you have to backtrace the signal all the way to the DAC. If the test is negative, then report here, there is probably some error which keeps the circuitry closed.

[cpucomp]

AW: cd liest, zeigt laufzeit, aber kein ton am ausgang

Hi Milan , Thanks for the reply. I allready have some news:
1 have the same Player again, it was not working at all! today I renewed the
Power unit (2 circuit breakers went constantly off ) after exchanging all Elkos the System went back to Service , C 47oouF 25V has had a short cut).
So I knew that this DAC PCB is ok. ( 1.769.280-12). with this board in place the cd-Player is doing ok.
so as first Action I replaced all C x on the defective board. Same faults!
I can hear the clicks of the volume Buttons, the Relais has the click as well..

Can you give me some detailed describtion what to do when searching the fault from the tail....?

I will be away for some 3 days (there is an aircraft with technical Problems tonight, they allready called me that I will fly with this aircraft to Brasil early in the sunday morning.)

I will be back tuesday...

hope to hear from you
greetings to belgrade

[MilanMilosevic]

Re: cd liest, zeigt laufzeit, aber kein ton am ausgang

Hello,

if I understand well, your CD player works fine with a DAC board from another B225. If this is the case, then obviously you have a defective DAC board.

1. Check if you get sound on headphone outputs.
2. Try pressing the CAL button and see if you get the 1kHz at audio or phones output (I doubt).
3. Play a test CD (burn one with 1 minute of 1kHz sine wave) and put in on repeat so that you have constant signal feed. Set the multimeter to 2 or 3V AC range, connect minus probe to chassis and use red probe to see if you have any signal on the following test points at DAC board (page 85/86 of the service manual): 14, 13, 12 and 11. You should see some steady voltage along the signal path.
4. Check output voltage at IC2 (LM337), TP8, it should read approximately -5V. This is the only voltage regulator on this board, others are coming externally.
3. Check the temperature of both DAC chips - you will find that they normally run hot, but not that you can't keep your finger on top surface. When you are already there, check if other ICs run hot.
4. Check all voltages at power supply.

And don't worry, this is easier than flying a faulty aircraft from Brasil.

Best regards from Belgrade.

[cpucomp]

AW: cd liest, zeigt laufzeit, aber kein ton am ausgang

Absolutly great!!! I will do it tomorrow... the aircraft is on take-off roll now, they could fix it . so tomorrow an other day for me of Stand-by duty ! I can not leave my house for 12 hours, in case of difficulties in one hour ready to go somewhere in this wonderfull world..... and plenty of time to care for my revox Babys..
I will Report to you any findings...

have a good weekend

[cpucomp]

AW: cd liest, zeigt laufzeit, aber kein ton am ausgang

good morning to milan

I am on the way to check according to your checklist:
1 no Sound at earphone outlet
2 calib i can hear very very weak on earphone and cinch (if b780 is full in volume)
3 not yet done
4 -5v are ok on power up, but are changing while manipulating Play, stop, cal tone, down to 4,4 to 4.7V =
5
6 voltage should be ok, because an other DAC-board is working fine in this machine

7. while touching the cases TDA 1540 to test the Temp both side I can hear a very weak "boooooom" on both channels

[MilanMilosevic]

Re: cd liest, zeigt laufzeit, aber kein ton am ausgang

Good morning,

the CAL tone is digitally syntesized and if you can hear it (even weakly), this means that the D/A conversion section is working. I would continue tracing the signal along the analogue path (number 3 of my post) because this is where the problem lies, almost certainly.

[cpucomp]

AW: cd liest, zeigt laufzeit, aber kein ton am ausgang

hi milan
second day was the day... out to Hongkong. Back now and time to electronic care... I checked all four Points no reaction, no ac mesurable. but found Diode near to Relais defectiv. the Relais is working now, the negative Regulator is back within the markings . everything should be working now.
But : the calibration tone is gone now. no weak Signal anymore, I am a litte bit frustrated!

In Hongkong I bought a Signal Generator (sines, square, zickzack) ttl, regular out , mV and Volts.
I have as well a oscillo and a power unit 0-30V /3A Twin/parallel out and a good multimeter. Transtester is on ist way...

Have a good day

[MilanMilosevic]

Re: cd liest, zeigt laufzeit, aber kein ton am ausgang

Two questions:

1. Was the relay working before replacing the freewheel diode D2? Please check if the relay is effectively conducting the signal with continuity tester on multimeter. When the player is turned OFF, you should have interruption between TP13 and TP14 and when the player is ON you should see continuity.

2. Did you test for AC along the signal path with CD player playing the test CD or with CAL tone on? It is the same, but just to check if you did actually play some signal through.

Sorry for asking the obvious questions, but this is similar going through aircraft checklists.