I've bougth a Panasonic RX-dT680
I made a serious mistake there after repairing the double deck (I made a big effort to find the wells that were broken). Happily the deck's work fine now, but when I was ready to test it, (I most recognice that I was very tired) I plug the unit into a 220V outlet AC instead of use the a 220-110V converter. As a result the unit was seriously damaged.

The BBX still works, but no sound.

Happily al functions, even the CD and deck logic works fine.
Taking apart the main board, the IC AN7134NR was clearly blown. This IC is a power amplifier that also includes 2 voltage regulators.
That's the reason because no sound, even on the highs (even when they use another separate chip). One regulator (9V) feed some equalizer and preamp circutry.
I 've bougth the AN7134NR today at Dicomse.
I solder it cerafully and inspected the board.

But when I plug it, no sound again. The heatsink runs too hot. I take the mainboard apart again.
I noticed that pins 5 and 6 are shortenned at the IC (6 is R out and 5 ground). That's a bit confussing.

I's the IC damaged ?

The output circutry is quite simple, only a series cap and a zobel network. Nothing that could resulted damaged because of my serious mistake.
Reading 5 and 6 position at board don't reads 0 ohms (that's ok). But reading betwen pin 5 and 6 from the IC read 0 ohms !!!!!

What do you think people ... was the IC bad before placing it or some section of the circuitry wich is damaged is burning the IC each time I replace it.

Thanks in advance

Pedro

For the curious people thast's the link to the datasheet ...

http://www.datasheetcatalog.net/es/datasheets_pdf/A/N/7/1/AN7134NR.shtml

R out to ground, sounds like it got shorted, iC is blown.

You should always turn the power up slowly after repairing any power amp.

Use a resistor maybe 100 ohm to to power the unit and test if it comes on properly.

well it sounds like there is more to that i am noticing that there is a ba3920 la4108 and b1185 you may have to check those also just to make sure they are working correctly

pedro i checked the la4108 its a audio ic also and the ba3920 i could not find anything about this ic it may well be tied to the amp as well

Thanks Ramon

I forget many things ...

The La4108 works fine, both chanels. I performed the easy test to touch imputs using my fingers and hums is noticed at tweeter output
Both channels work.

The La 4108 is for highs and the AN7134NR is for low. Also this chip inlcude 2 voltage regulartors. One 5V and one 9V. Because it has stanby control, looks a nice solution even as a supply control .. is like all in one solution for BBX with logic.

The BA is something like a supply control. It doens't clear for me what this IC does in the cricuit.

The strange thing is, after an overvoltage, any part of the circuit could be damaged. Ok.

But output cicuitry is quite simple, and the short don't appear when I removed the chip. In both channels.

The only one I guess is something could be worng with anther section (for example regultaros, may be burning the amp section).

The next time I bougth the AN7134NR I'll check the shorts first ... because this is IC is obsolete .. and I don't know were the dealer had found it.

That Transwave say is the best way to work. I have done it several times. But RX-DT680 had all borads arrange in an strange way so it's imposible to measure until you have all put in it's place. Esay to take apart .. but difficult to test inside.

But I'll try to do this ... But I'm really feed-up and worried about this.

Thanks for your tips people

Pedro

pedro applying 220 v to a 110v radio is going to do some very serios damage..the thing was to make sure the power supply is still putting out the correct voltage,and make sure those diodes are all working,,as it seems the amp section took a hit as the power supply feed to that point, there are a bunch of caps and behind the main chip there are 2 diodes make sure that one of them or both are not open causing the ic chip to burn out small stuff like that ruins your day and most of the time is overlooked....

Use a small power adaptor with a 3,4, 6,9,12 volt switch.
Bring up the voltage, see if its working ok.

I see maybe the part was defective when you bought it. ??!!?

Today I talked with electronica Matsu****a (the oficial service of Panasonic in Argentina)
I spoke with a technician who knows the RX-DT680 quite well. He told me that he had seen several mitsumi fake parts. Also told me that both the BA3920 and the 7134NR are obsolete parts. Because of that they won't accept my unit

That transwave said makes sense. And about the IC, it could be true that the chip was bad.
I'm figuring what thing could damage the output, no shorts to ground were found on the PCB, no speaker conected of course ... It's a hard one.
There is an issue, that chip has 2 regulators inside appart form the twin power amps, that provide 9V and 5V to be used in different BBX section ... I'm going to check no shorts on this ouputs .. But I can't stand one section damaging another. Regultors inside hace a 300mA limit ...

To be sure the next time I'm gooing to carry my multimeter and check output pins at the shop.

31 Mar 08 Panasonic RX-DT680 Boombox 110237416994

i have one of these but i dont like it too much. Ummm
100_3196 Panasonic RX-DT680 front flash

100_3197 Panasonic RX-DT680 front

100_3198 Panasonic RX-DT680 back

Yes, that is a Panasonic RX-DT 680. Gold star for DM4U

If you don't like it then sell it DM4U, I'm pretty sure Success may want it.

That's a goood idea !!!!

But it's a little sad to crap the unit morover when it was caused by a very silly mistake.
Figure that ... it was runig ok when I bougth .. but no the twin decks ... (alway the same). Now the twin decks work ... but no sound
Then ... the unit is more damaged than when it was purchased. Also the previous owner has care it very well. Even CD works fine with very scratched CD's !!!
I would preffer to get running this one , but if I can't ... I'll go for one like dm4you if he really wants to sell it.
It's a nice system !! and of course is a Panasonic !!

Seeing the service manual for the DT680, main power supply is about 15V ... and the AN7134NR is rated until 24V, actually is feeded with 14.2V . Even with a blown regulator the system amplifier most work .....
I found another dealer who has AN7134NR ...
Second chance ...

FIXED THE MAIN ISSUE !!!!
The four amps, radio and tape runs OK !!!

What happened ?

The IC was bad !!!!!!!!. Putting a new one bougth in another dealer work fine without touching the main board !!!!!
Ok, I spent lots of time checking it, and of course some point in another board that use the 7134NR regulators ...
I run it heavily to test the IC for 4 hours. No problem.


Now, some problems with CD player (
sometimes NODISC, or weak sound, but sometimes reads and sound perfect)

A minor issue with deck keyboard ... sometimes reads REW and FWD instead of PPLAY in each direction. That happened prior to the accident, so it isn't related to this =)-
Because this keyboard was made using only one analog imput (and a resistor network to generate a variable voltage diferent for each button) I guees some cap or noise could prevent this keyboard of operating fine.

pedro good to here you got it working and hopefully you will resolve the rest thats left

Thanks ramon for your help.

But I'll spent some hours to see the rest of the problems.

Also I was thinking of giving it a true line in. The idea of putting a computer CD and keep the CD running to take advantage of the CD out as input isn't fine.
Also, the CD preamp forces some signal on the CD out that I need to override with my imput, resulting in a weak sound ...

I was planing to take the imput capacitor form the equ board apart and hock the input there. My idea is avoid permanent changes on the BBX, OF COURSE, both board and case. Still thinking ...

Pedro

well pedro i would leave it alone you dont want to mess something else and then go crazy

That makes sense

Ok ... let finish that RX-DT680 and put it on a shelve.

Wait for another RX-DT680 to come,
avoid pluging it without the 220-110V adapter and then .. only work in the line-in instead of work wondering burned IC's !!!!!!

The tape deck issue could be those sensors which are located right above the deck. A quick brush with a nail filer will do the trick.