Onkyo Tapedeck TA2350 nimmt nicht auf

Marcus,

Your erase/bias-oscillator is not working.
It can have different causes.
The cable from the oscillator to the erase-head may be broken-off the head, that's rather common.
The oscillator itself may be defective. Usually it's build around just one or at least very few transistors and the oscillator-coil.
The power-supply for the oscillator may be varied to adjust the bias-output to suit different tapes.
This switching of the power-supply may be defective so the oscillator doesn't get any power at all.
The transistor/zener-diodes/electrolytic capacitors in the oscillator may be defective.
Also the oscillator-coil itself may be broken.

Really impossible to say without doing some measuring inside the tape-deck.
Unfortunately I don't have the service-manual for this deck, so this is it

mfg,

/tri-comp

Bei einem solchen "Standschaden" würde ich zuerst auf einen reinigungsbedürftigen Aufnahme/Wiedergabe-Umschalter tippen. Das ist ein echter Standardkandidat, wenn ein Tap elektronisch spinnt.

Ein oder mehrere Relais an dieser Stelle würden solche Probleme vermeiden. Diese (elenden) Schiebeschalter sind
doch "nur" eine Anzahl Wechsler.
Ist denn eine Schubstange/Feder , ich sah auch schon Hubmagnete für SS-Antrieb (was ja funktionell ein Relais wäre), billiger als ein paar Relais ?
Aber immer diese halboffenen Schiebeschalter
anstatt gekapselter Relais. Oder HalbleiterAnalogschalter.
Was denken sich eigentlich die Entwicklungsingenieure was Langzeitstabilität anbelangt ?
bukongahelas

Hallo bukongahelas,

Was denken sich eigentlich die Entwicklungsingenieure was Langzeitstabilität anbelangt ?

Es wurde schon oft diskutiert. Es handelt sich um Unterhaltungselektronik. Die Vorgabe an den Entwickler lautet dabei nicht "gut, teuer, langlebig", sondern:
"schnell auf dem Markt, billig, Haltbarkeit ca. 10Jahre *)".

Ein Entwickler ist kein Manager und Entscheider, sondern ein kleines Würstchen in einer Firma. Andere entscheiden, was er zu entwickeln hat. Er kann dem Management seine Bedenken sagen: "So wird das Gerät aber nur 10 Jahre halten!".
Aber das wird kaum sagen, dass das zu kurz ist.

Konventionelle Relais sind übrigens keinesfalls langlebiger.
Gerade für solch kleine Signalspannungen muß man entweder Reed-Relais verwenden, oder vergoldete Kontakte -> nicht ganz billig.

Am besten sind da einfach elektronische Umschalter.
Die wurden ja auch dann eingesetzt. Aber wohl eher, weil sie dann billiger wurden :-)

Gruß
Bernhard

*)Das galt damals. Heute sind 2 Jahre das Ziel....

audiophilanthrop schrieb:

Bei einem solchen "Standschaden" würde ich zuerst auf einen reinigungsbedürftigen Aufnahme/Wiedergabe-Umschalter tippen. Das ist ein echter Standardkandidat, wenn ein Tap elektronisch spinnt.

Hallo Stephan,

danke für den Tipp - nur habe ich als Laie keine Ahnung davon, wo sich dieser Umschalter befinden soll/wie so einer aussieht.

Ich habe das von tri-comp beschriebene Kabel zum Löschkopf geprüft: Ok. Wenn ich die Bias- oder Rec-Level- Potis drehe, dann kommt mehr auf dem Band an, aber das Löschen an sich funktioniert gar nicht.


Marcus

Hallo Marcus,

der erwähnte Schalter ist ein langes Gebilde (meist ca. 7 - 10cm lang, vielleicht 5 - 10mm Höhe und Breite).
Er wird betätigt, sobald du die Aufnahmetaste durchdrückst!
(dazu die Löschsicherung natürlich entriegeln).
Dann siehst du, wo sich im Gerät was bewegt!

Gruß
Bernhard

Hallo Bernhard,

ja, mein Kassettenrekorder aus Kinderzeiten hatte sowas. Aber dieses Tapedeck nicht. Wenn die Aufnahmetaster gedrückt werden, dann fährt ein Motor die Tonköpfe hoch an das Band, das Band läuft an, Zählwerk läuft. Mehr passiert da mechanisch nicht.

Gruß
Marcus

Hallo Marcus,

ok. Das ist doch eine Aussage! Dann werden wir wohl in die von Tri-Comp vorgeschlagene Richtung suchen müssen!
Leider habe ich keinen Schaltplan vorliegen :-(

Gruß
Bernhard

Here's a chip that does electronic switching:
http://www.classiccmp.org/rtellason/chipdata/ba3420.pdf
No moving parts of a relay or slide-switch.

Here's an old Akai with a slide-switch:
http://www.radiodatabase.nl/toestellen/akai/CS-705D/CS-705D.pdf
On page 10, fig.10 there's a drawing of it. This represents rather good how most of them looked. This is an old model, newer taperec.'s have narrower and possibly longer switches. Some even have 2; one for right channel, one for left. This is a combined switch in the Akai.
The switch is the vertical rectangular shape between the two VR1 trim-potentiometers extending to the top-edge of the board.
It's function can be seen on the very last page of the manual. It is to the right of the 5-pol DIN connector at the left of the schematic.

If you can't find something inside your recorder that looks like what you see in the Akai, you have an electronic-switch type is my guess.

Now to your problem:
Being able to vary what gets on the tape with the Bias-pot's suggest your BIAS/ERASE-oscillator is running!
BUT, it's doing just half of what it's suppose to. The BIAS get's where it is suppose to go (REC-HEAD) but the ERASE-signal (To the ERASE-HEAD) isn't getting anywhere.
The ERASE-Head could be open (NOT likely), the Cable could be broken (It moves every time the HEAD-Bridge moves) or the signal is lost in the mechanical or electronic switching. With a scope (and some experience) the fault can be found in seconds

mfg,

/tri-comp

...and then maybe it's done VERY differently!!!

I looked at an Onkyo schematic I have for the TA-2630.
In that model everything is done electronically.
EVEN the BIAS circuit is special, including the BIAS-Adjust.
There IS a BIAS/ERASE-oscillator block of course. It's supply voltage is varied according to the TAPE Type used. METAL-Tape requires much higher BIAS/ERASE than Ferro-tapes.
The ERASE-Signal is fed straight to the ERASE-head via a cable, but the BIAS is special.
BIAS taken off the Oscillator-block in injected into a uPC-1297CA chip and NOT directly mixed with the audio on it's way to the REC-Head. BIAS-Adjust pot's are also connected to the uPC-1297CA, so it's not easy to predict how they work if the Oscillator-block is not running at all.

Time for you to look under the cover and write what IC's are inside.

EDIT:
I only have the schematics for the TA-2630, not the complete service-manual. I found a data-sheet on uPC-1297CA it it really IS something special. It has a form of dynamically variable BIAS-control to set the BIAS according to the Audio-contents (Volume). This system was invented by Bang & Olufsen of Denmark and called HX-Professional (HX = Headroom-Extension). NOT something to be found in the TA-2350.
Just goes to show how difficult it is to take into account all variables when trying to do a remote diagnose
NOW, about those IC-markings.......!

Hello tri-comp,

I have to correct my earlier statement that turning the bias-potis changes the result. That is not the case. Only turning the rec-level potis change the result.

When looking at the board and comparing the layout with other Onkyo models, then I realize or at least assume that the elements on the board are grouped by funtion and each group has its own number range. Every element around the bias is numbered in the 400 range. There are two chips in that range:
BA6251 and M5218. I believe that I have identified the coil of the oszillator. There is a transistor D947 close by.
Here's a photo of the area: http://picasaweb.google.de/114972170221098720999


Other chips on that main (audio ?) board are:
M5218L
IR3702
4558DX
4558S
78M12
78M12A
7805A
and two Dolby chips: HA12090NT

and on the other, smaller board we have:
LC7800
M54544AL (twice)
and one Onkyo chip: LM6402H425


I don't have a scope and can only measure voltage and resistances.


Marcus

Hi,

Well, based upon your info (...and a lot of looking through manuals and a few bright ideas ) I came up with this:

Your Oscillator-Coil is in fact an Oscillator-Block.
It contains all electronics necessary for the oscillator including one or more transistors, resistors and capacitors.

The Block is a type NOB-029 (Onkyo partno.:24606198)
I have Googled the NOB typeno and found NOTHING
I think ALPS used to make some, not sure...

ASWO, Germany has SOME parts for TA-2350. They don't have the Oscillator-Block, but they used to. Most importantly; they had the Onkyo Partno. given above.
From that on it was just looking through my Onkyo-manuals until I found another recorder where they used the same Block.
This turned out to be the TA-2056 ...AND possibly others, I just stopped at the first one found.
Now I can see how the Bias/Erase Oscillator Block is wired, so here goes:

PIN-1 is connected to Ground. That should be easy to identify in the TA-2350

PIN-2 is the direct output to the ERASE-Head.

PIN-3 Positive Supply-Voltage. This is variable (BIAS-Adjust), see below ***

PIN-9 is BIAS-Output and not very interesting in this case.

PIN-10 is Negative Supply-Voltage -12V


***
PIN-3
Between Pin-3 & Pin-10 should be measured a voltage roughly according to this table (for a TA-2056 recorder):

FE-Tape = 7.17V
CR-Tape = 12.5V
ME-Tape = 19.8V

Note, that there is an external Electrolytic capacitor across PIN-3 & PIN-9. It may be shorted and have caused supply-transistors to die.

-----------------

Now, if you have supply-voltage reaching the oscillator it should work. If not, you're in trouble. I have been inside these blocks before and have successfully repaired several. Different things may happen.
The transistor (Transistors) is defective; replace it and check this:
A parallel capacitor on the output-winding (PIN-2 to PIN-1) may be shorted.
Internal resistors may be burned (Emitter-resistors, low Ohm)
Higher-value resistors in transistor base circuit may have increased in value.
Oscillator-coil is broken. You need to rewind it yourself; nowhere to get a new one in my opinion.

Of course you may get lucky and discover a whole new problem yourself

PM me if you need info from the TA-2056 manual.

mfg,

/tri-comp

EDIT:
Removed a couple of spelling errors.
Feel free to find more yourself