problem with Melos Echo Chamber

[spy]

Just found a non working Melos with 3 cartridges. They look like Dictaphone but I'm not sure as there's nothing written on them.

For some reason I don't have the wet signal. But the play head seems to work as I can heard the connection on the tape everytime it passes the head.
Also, I have the signal with the bias frequency on the record head. But how can I know if the record head work?

Does anyone have the same experience with an Echo Chamber? What do you suggest me to do?

[52 Bill]

A tape head is really just like a pickup/choke, a coil of wire with a metal core. First test with your ohmmeter for coil continuity.

Have you demagnetized the heads and tape path?

[spy]

ok, just tested the heads with an ohmmeter and there is continuity. So heads are ok...

Now the hard thing.... I don't have a demagnetizer!
Is there any simple way to demagnetize them? How do you guys do it?
And are we sure that the problem is there?

I did a search about it and it seems that I need a demagnetizer! How much does it cost one?

EDIT: You can find a lot of them on ebay! They are not too expensive.... there are a lot around $10!
Before I buy one, is there any recommended demagnetizer?

[spy]

Found this one!
Tape Deck Recorder Head Demagnetizer,Reel to,Cassette - eBay (item 400076917722 end time Dec-02-09 11:16:59 PST)

Any good? Does it worth it? Remember that I have to pay another $12 for shipping... as I'm from Greece.

[52 Bill]

I would think that you could find one of these in Greece.

Any basic demagnetizer will work. The one you found on eBay should be fine. I use one that I have had for 40 years. Still works, but I don't use it very often anymore.

[cjlectronics]

Do a search on eBay for a Univox EC-80. Does your Melos tape echo unit look the same?

I think that Melos is a re-branded Univox tape echo unit?

[spy]

Unfortunately, I didn't find any demagnetizer locally! Ebay is my last chance...

CJ, yes it's the same with Univox! I'm checking the unit with Univox's schem...

[cjlectronics]

When I see a problem like this, I always check the bypass switches and bypass jacks. I've been burned by not checking these items first and have totally dismantled an effects unit never finding anything wrong then discovered the bypass jack had an open contact. Many times the wet or effect signal will get routed through the bypass jack before being wired to the effect out jack.

Check the mechanical high wear items first before dismantling anything.

CJ

[spy]

Happy New Year friends! Hope 2010 will be much more better for all of us!

Today I found some spare time to work on my Echo Chamber. A few weeks ago my new demagnetizer came to my door. So now I can demagnetize heads!
Nice tool and I'm happy with this purchase cause I'm planning to go analog to my recordings so I'll need it again in the future.

The sad thing is that I demagnetized Melos' heads with no luck! Then I remembered that I haven't checked with an Ohmeter if the Record/eraser head is good. I have measured only the playback head. And I measure infinity both at the record and eraser head! Both are in the same enclosure....

I'll try to find locally for a new head but I don't feel that I'll find one. If I won't is there any internet store that sells heads? Also, how do I order a head like this? There isn't any code on it!

[spy]

ok, no luck again!

The heads are just fine. I measured them again and they're fine. I didn't measure them correctly the last time. So, the problem isn't the heads.

I demagnetized them again and nothing.

Any help?
The unit reads, I can hear the joint of the tape from the speaker but it doesn't record.
I measured all the transistors, voltages, resistors and everything looks perfect.

Any expert that would like to help?

[oc disorder]

Sounds like no record bias.
Need a schematic for that one and a o'scope wouldn't go astray either.
Check the coil,capacitors and the transistors nearest the rec head.

[spy]

The weird is that the record head has two heads in one. Like a stereo head. I suppose that one plays the role of recording and the other of erasing. Is this correct?

I can't find the exact schematics of this unit. I found Univox EC-80 and EC-100 that are similar but not the same.

Melos is like EC-100 but there are three heads. One for playback and two more in one.
I checked with an o'scope the last head and there is a high frequency stable in one of them and at the other there is a high freq that changes when I turn up the volume. I suppose that this the record head with the bias on the signal...

EDIT: Thanks for the schem! It's like the first one I posted. But it's not the same with Melos... I have three heads and there is not an input transformer in mine. It's a little bit different. Check the other schem I posted that has 3 heads. But Melos doesn't have opamps!

[spy]

Just wondering, but how must be the signal on the recording head? Any schem?

[oc disorder]

Before getting too complicated maybe you should check the cartridges.
I assume one of the 3 should work but it is possible the oxide is worn off
and or the felt-sponge-fabric in the cartridge is not applying enough pressure
on the tape to press on the record head.

The "double" record head is interesting.
It would not be stereo as it would be a full track (mono) covering the width
of the tape.An old mono cassette deck head may work as a playback head
but it would be half track and not cover the width of the tape.
The record head I think would be impossible to get - must have been custom made.
The head could be worn and need some additional azimuth adjustment.
Perhaps it is bent back at an angle from a previous owner forcing in a cartridge.

It seems there are 2 coils that share the same metal piece in the head.
( I don't know the correct name).
Perhaps that way the bias and the signal are magnetically coupled (joined)
providing a simpler circuit.
The Melos seems to have the majority of the EC-80 circuit but with the improved record/bias of the EC-100.
I'll attach a joined schematic incase some genius may have a bright idea in his coffee break !

There must be a permanent magnet for an erase head .
I noticed that these also have another brand name "Stage".
If you have an oscilloscope and an oscillator you should be able to see the signal applied to the head.
You did say
"I checked with an o'scope the last head and there is a high frequency stable in one of them and at the other there is a high freq that changes when I turn up the volume. I suppose that this the record head with the bias on the signal..."
Thats why I now think its a mechanical problem alignment etc.

[spy]

I checked the cartridges and in one of them I added pieces of felt for additional pressure. But nothing...

Yes, there is a permanent magnet for the erase head.

What I can't understand is the "double" head. Of course it's the record head...
But I checked the signals in both coils and in both of them there is a high frequency. Same freq and same Vp-p. In one of them is stable but at the other it changes in amplitude with the applied signal!?

So, in one of them is the input signal with the bias but what does the other head with the high freq do?