M12 problem

[cavemaen]

Hi Raffaelo!

Do you have a Service Manual?

The DIN - Connects are symetrical!

The broken Fuse are a Problem.

Look at the Voltage-Stabilisator!

Regards,

Rudy

[cavemaen]

Hi Raffaelo.

Now, the Connects are symetrical. Pin 2 is hot, Pin 3 is low.

Without Manual you don't have a Chance to repair.

I have Manuals from M15A, M21, EMT and Nagra. My M12A is running.

I'm looking for a Manual, but it is very difficult...

Best Regards,

Rudy

[erich]

hi,

on the play amp I find only one IC. this is an LM380N ( op amp ).

regards

erich

[erich]

Hi Sip,

what is the problem ?

If the taperecorder don´t play, you can´t have sound ....

regards

Erich

[david77]

Hello Sip.

I had a similar problem with one of my M12 tape machines. The fuse on the oscillator/voltage regulator card was blown and I had no output. In my case the problem were some shorted capacitors.

Does the heatsink on the oscillator card get very hot? If so, I would recommend you replace all the electrolytic capacitors on that card and maybe even the tantalums. The capacitors used in these machines (ERO, red-brown housing) are known to cause
problems.

Regarding the diode on the logic board:
Do you have the newer version with CMOS IC logic controll or the older version wich uses only relais?
The new version has the SUB-D 15pin. connector for the remote control, the old one has a WIST10 round 10 pin
connector at the back with a dummy-plug in it.

Does the tape transport work at all?

If you need further assistance, I have a service manual for the M12A.

David

[david77]

Hello Raffaelo.

OK. My service manual also covers the M12, without "A", so it's the right one for your machine.

This IC you mention is on wich card? Is it on the left side on one of the REC/PLAY Amplifiers or is it on
the right side, the oscillator? Is it on the same card as the heatsink?
In the manual the voltage regulator IC is LM723 and the operational amps on the playback cards are LM380.
Maybe it has been replaced before? I can not find a datasheet for it.
The regulated output of the power supply should be 30V DC. You should be able to measure this on the OP-AMP's
pins 7 and 14 (audio cards!).
The unregulated voltage (measured between 0,315A Fuse and ground) is about 38-40V, if I remember correctly.
The heatsink should not get very hot! If it does there's something wrong.

I'll have a look at the circuit diagrams tonight. Then I can tell you more.

David

[david77]

Hello again.

I had a quick look at the manual now. The regulator IC is a LM123 (equiv: 723). The OP-AMP's are LM716 in
round metal cases (TO-99).
The output voltage of the regulator circuit should be 30V +/- 0,5V. You can measure it between contact
10 (GND) and 12. The unregulated input voltage should be measurable between contact 2 and 10 and should be somwhere
between 35-40V (from memory).

Contact 1 is near the top edge of the cards.

I suggest you do the following:

1. Remove all cards from machine, except oscillator/power supply.

1.1 Check if 30V regulated voltage is available.

1.1.1 If not, check the capacitors again, especially C1 (Tantalum 4,7uf). This one was shorted in my machine.
It's the one on the back of the card directly next to the little slot.

1.1.2 If power is OK, plug in one card after another and re-check the supply voltage (+30V).

1.1.3 If supply breaks down while doing this - BINGO! You've got the card resposible. Check its caps again.

1.2.1 If power is correct, try changing the U5B... IC. The original LM/uA716 IC seems hard to come by these days.
You might try another type, maybe the LM380, which is used in the later models. It is, however, not pin compatible.

If you want the circuit diagrams, let me know. I can scan them and send them to you.

I still strongly suspect the electrolytics!

David

[david77]

Hello Raffaello.

I will send you the diagrams of the Playback amps, power supply and the wiring diagram tonight.

I think the machine should work without the Pilot amps present. As far as I understand the manual,
there is no reason why it shouldn't.

Have you checked for the +30VDC from the power supply?

David

[cavemaen]

Hi Raffael,

do you want a good M12A in stereo?

Best Regards,

Rudolf

[cavemaen]

Now, 19/38cm (7,5 / 15ips) with AEG Adapt. XLR, 19"-Kit without VU, sorry.

I think: 250,-€

Regards,

Rudy

[ghe67]

Now, 19/38cm (7,5 / 15ips) with AEG Adapt. XLR, 19"-Kit without VU, sorry.

I think: 250,-€

Regards,

Rudy

HI Rudy, the machine is still for sale?
If it is I would buy it.
Thanks
Giorgio