The last issue that I need to solve and close my RX-DT680 ...

The issue looks appears about the 50% of the times. When I press ">" the system executes ">>" and when I press "<" executes "<<". Sometimes "<<" executes the "REVERSE MODE FUNCTION"
Both decks do the same (the DT680 has only one set of key for both decks with a deck selector key).
Also the display shows ">>" instead of ">" showing that it ins't a mechanical issue (both decks can't have the same fault) but the system procesor fails on reading the key.
Of course many times the system read the key fine ...

Looks like the BBX gone mad .. but look at the circuit. What Panasonic have done is use a resistor chain and using an analog input at the procesor reads all keys with only two wires.
Too clever ... but playing with the resistor chain .. you see that the voltage diference betwen ">" and ">>" is only 0.08V !!!! is too little ... The same difference is betwen "<" and "<<".
What do you think ?. The switches are bad .. or perhaps some filtering cap ?.
Note that other keyboards of the system (CD an turner) are built in the same way ...



Thanks

Pedro

not sure pedro but how many times does the switch fail? i am not saying that it does not happen a cap maybe a bad solder joint it happens too. and you know that a bad solder joint can make the deck work and all of a sudden it stops then you wiggle the board and it works again so saying that it could be anything i guess the way is doing one thing at a time to see what you fine

Ok, let me ispect the swithc board well.
Yeah, after some years soldering can be a problem. I'll check that first.

About the number of times, I would say 50 over 100 times one fucntion is missread.
Not all fucntions, but play and reverse play are read as FWD and RWD.

A very rare one .. I guess that this keypad method is used usually since reduces the amount of wire.

A most said that I lost the remote
But if with the remote works fine .. definitely the problem is with the keyboard readigng.

It isn't so bad. After the first missreading, I try againg and it's ok. But I'd prefer to work as new, more that is a nice system.

Thanks Ramon.

I'd prefer old school boxes definitely, like you said.
Only think, if the main processor crash no more BBX. And foget to chenge it. At most, if you are lucky you can change the whole board.
I Remeber a Sony FH656Cd. Nice minicomponent.
But the main procesor had a reset issue.
So it works fine all the time until you unplug.
Then you need to unplug and plug several time until the procesor starts running. Without procesor, no CD, no amp no decks nothing.

Definetely mechnical decks and at least some IC with legs that I can solder PLEASE !!!

Let me said that I've fixed it.

The problem were the PCB switches. They were worn-out. I guees that the debounce made at the main procesor for the switch reading isn't so good and fail when switches made a lots of noise while closing the contact.

I've changed them and works fine. I've also change some from the CD functions.

Pedro.

thats good pedro where did you get your parts?

I've bougth the switched at a little electronic shop at 10 min from home.
The IC at two local dealers, the first (burned) at Dicomse and the second at another electronic shop called "Arcomel".
The teethwheels at another shop "Electronica Universo" with is dealer of a manufacturer called "electrogoma", who makes belt, pinchs, tires and tethwheels for Video, audio and printers.
They have one representative in MEXICO, so you can get parts to fix your decks. Good quality replacementes. They have a large brochure of belts, so you always can find one to match your requirements.

Pedro.

Pedro, did you uploaded any pics? i dont see them.

That was taken when I bought it, 3 months ago, and without cleaning. Nice condition indeed.



That was taken 3 says ago. The PCB switches weren't changed yet.
I has a very hot day (for my country). Around 39 centigrad, so I decided to test the amp at max load for a half an hour to be sure that further problems won't appear. It has passed perfect.



I'll take some today. It's assembled and cleaned.

Pedro

pedro looks better without the front cover leave it like that

Perhaps when I have bought the seventh unit of this model I'll try this terminator mood , and the line in also.
I'll try this with an egg, perhaps that improves the look of the device.

What modification, besides a lower ohm speaker replacement, could you recommend to help it produce cleaner mid bass at high volume? Because that seems to be the only flaw in this unit as far as bass goes. This thing has impressive bass overall, especially in the low frequencies. It will belt out those low passages better than many mini systems. The only problem is the mid bass which I can't figure out considering how well it does with the more power hungery low tones. For example, if a 45 hz note is being produced, the speakers move violently and the sound is clean and pure for a boombox. But with a 85 or 90 hz note the speaker movement lessens and distortion sets in as the volume is increased. This confuses me because it clearly appears that the speaker still has some x travel to utilize to help produce a clean mid bass sound, yet with the 45 hz note, the remainder speaker travel is utilized completely to take advantage of moving the most air possible, which requires more power. So here's my ultimate question: Why does the less powerhungry midbass distort especially given how well it produces the more powerhungry low bass?

That's a complex one
Firstly, but I'm not sure of that, speaker travel decrease as test freq. increase.
The speaker mechanics aren't fast enough to follow a high frec waveform. At this point the woofer is like a lowpass filter.
Also, there's an Eq in the signal path.
Phase shift and some distortion is expected.
The IC AMP itself isn't so good. It has a high THD at rated power, that's Ok since only drive the bass.
Have you tried another speaker to test the low freq. amp ?
I guess you can change some filter gain in the Eq. setup, but too much gain would shield distortion.

Pedro

Yea you're right. As a general rule speaker travel does decrease as the freq increases. The reason why I discussed the speaker travel with the different frequencies is because you would think that the lower freq. which move the speaker more would be more prone to distort. But it's the other way around. The higer freq. (mid bass) which move the speaker less are the notes that distort. Why is this?

Have you tried to disconect the mid highs from the amp (altougth there is a crossover before the power amp, much low freq. program goes to the highs and much high frec program goes to the woofers). That's: perhaps the distortion is caused by the mid/highs ...

Yea. And I'm sure its the woofers where the distortion is heard. I have tried to see if there was a difference when ever I use earphones and it does the same thing, which leaves me to believe that it's the amp not the speakers producing this distortion. To see what I mean, play a bass CD and listen to the different frequencies from the higest bass to the lowest bass, and you'll see what I mean. If you listen through a head set, the distortion charateristics are the same. You mentioned something about the IC AMP not being so good and it having a high THD rating. You also mentioned that because it drives the bass units the high THD rating was therefore ok. I'm wondering if the high THD rating of the IC AMP could be the culprit in causing the high bass to distort. Because maybe the high bass that distorts is near or at the freq. at with the IC AMP's high THD rating starts to take effect. Hmmm, what do you think? Because if this one defect in the RX-DT680's bass reproduction could be addressed, this box would be so KILLER!! It already is one of the best BBX's out there.

Uhhhhhhh huh? This seems Greek to me. I save this for the electrical engineers. In any event, how does this information translate to distorted midbass? And what can be done on that side of smart to fix it? Thanks for sharing, by the way, I think I'll be able to learn a lot from both you and oldskool!!

Oh, my bad, I realize what you're saying now. You're saying that since the IC's THD generally decreases as the freq. inncreases, then the IC can'tbe the culprit, as I suggested. Sorry! So what do you suppose may be the reason this unit does not produce the midbass as cleanly as it does the low bass at higher volume?

IU'm not sure. But you can try defeating the EQ control in the 680 (that needs to be done internally). If THD goes down at the IC and speaker works fine, perhaps is sometinhg in the signal path, like the EQ board and the active crosover wich divides the program in both, low and high frec program to feed the low and high amp.
Any filter in the signal path could be suspicious.

Thanks for your suggestions. I'm all ears as far as that goes. I'm eventually going to write a letter to Panasonic to see if they would be willing to upgrade this unit to increase the power and the sound. For lack of a better term, pimp it out! So I'd like to have an idea of what internal changes could be done to help accomplish this. Thanks again. In the mean time, I will try to educate myself on your suggestion so that I can understand what all it involes. Maybe I can find a local repair shop that would be able to implement what you suggested. I just want to make sure that I can accurately communicate it first. Thanks again!!

Eq defeating and crossover defeating is only for testing tasks. When I say defeat is bypass the EQ. and see if the problem is still there or not. You most know that capacitors (electrolitic) in BBX are a serious problem, because the aging. Its value changes along the time, and a 16 year electrolitic is for sure out of specs. So before complain Panasonic, you will need to recap the unit (at least those caps that are in the signal path).

I have talked to Panasonic, to fix my 680's decks, but they say that the teethwheels were not long avaible. The main fact is Panasonic won't service or support a unit that's 16 years old.

Pedro

Okay, so it's possible that this unit when brand new didn't distort the midbass? I have three DT680's and all of them do it at high volume. If perhaps recaping them would solve this, then I'd be willing to do this. Have you ever done this to yours? If so, how does the midbass and the low bass perform when the S-XBS and the volume are cranked? If you havn't do you know anyone who has?

My RX-DT680 have suffered enough fixes ...
At the moment is sleeping on a shelf and fully working.
But I'll test that you said. I'll record a CD with a 90Hz wave and we'll see.
I don't know somebody with this system.
This model has been imported in very little quantities in Argentina because it was expensive and people prefer buying hughe and cheap Aiwa minisystems instead of good quality but expensive Panasonics.

Thanks man!! I'll look foward to your feedback. If you are able to, try to record a series of bass freq waves from say 45 to 100 hz for an audible comparison. Thanks again!!