Tandberg 2041 (series 2000) Erase Head Problem.

[scottie_UK]

Originally Posted by ricard

Well, quite frankly, these recorders are approaching 40 years of age, and they were probably not designed for that lifespan. So as a whole or at least individual recorders are bound to have issues after this time.

As I think someone might have mentioned, a dodgy record/playback switch due to oxide or dirt could cause a reduction in recording bias, or complete lack of high-frequency erase/bias signal, and intermittently at that.

It can be very frustrating to get a machine like this to work properly if there are intermittent problems. But given time - and rest - you'll get there in the end. The road is just not as direct as one hopes at each step of the way.

The lego stud idea sounds like something that would be worth trying.

Thanks for your encouragement I'll keep on for a bit. Part of me is determined to get this running right, the other part of me says, get a Revox.

[scottie_UK]

So, ok I'm sure I have the alignment of the erase heads right, but why does it not erase properly. I originally went along with the tape tension issue (because this was an issue). However, even if I press the tape up against the erase head, or move it up and down a bit it fails to erase the tape with approximately 20% of the underlying sound getting though.

So you think this could be the switches at fault, or a broken head? how expensive are replacements? Also, I have some switch cleaner would that be good to use in this case?

[ricard]

If there is some erasure, but not complete, it indicates that the erase head is ok. The most common failure mode of a head is an open winding which would leave you with no erase at all. That said, the bias introduced at the record head also provides some erasure, so even with no erase head the original recording will get muffled. But "20% leaking through" sounds like the erase head is doing its job.

So it would seem that for some reason the erase voltage is too low. It could be bad connectors or contacts, something wrong in the oscillator circuit, or something wrong in the power supply section so that the overall supply voltage is low in the machine.

It could also be that someone has turned the recording bias way up, leaving too little for the erase head. I had this happen to me on another Tandberg; the machine had been adjusted for some high-bias tape, so it wouldn't erase properly because the erase head got too little drive (and also the high-bias tape of course required a larger erase signal to start with).

If I remember correctly, the type of switches used in these machines are quite good, rarely requiring cleaning. It could be worth trying a good contact cleaner such as Kontakt-60, sparingly, a short jet into the contact assembly at one end, let gravity spread it into the innards, wipe the excess off, and operate the switch several times to get the cleaner to do its job.

I would have tried to measure the voltage at the erase head, I think the service manual gives a spec for it. Either with an oscilloscope or VTVM (or whatever the equivalent is called these days); an ordinary multimeter might not show correct readings with high-frequency AC.

Also, measure the power supply voltage in the machine. It's supposed to be 26V or something (check the service manual). It's easily done and could be the root cause of a lot of symptoms.

[scottie_UK]

I'm guessing that the previous owner being of a church background, and providing assorted tape brands that the innards were not tinkered with.

[DOFFERY]

Scottie, have you a VTM or even a digital meter to measure the erase voltage?? It should be aprox. 90 volts on each section. Have you resolved the stiff take up table?

Ricard , you are right regarding the pressure pad enabling the loop to be eradicated on pause, we agree on that. However in practice I always reduce the pressure on the pad due to it getting easily flattened hence increasing the pressure above that stated , the slight reverse torque on the supply spool assists in smooth running & still erasing correctly. The pressure pad on the erase head plate is "grooved" & springy easily worn flat , also collecting rust . Just my policy over many years .

Colin.

[ricard]

Colin, great info, that type of long-term information is seldom learned from the service manual, one needs many years of experience for that. I've noticed too that the reverse torque seems to supply quite a lot of back tension - perhaps it increases over time as the felt discs under the reel tables get flattened too? I.e. the reverse torque on the supply reel slowly increase over time?

I think in my mind I've been thinking of the model 15 vs. the 14 which are virtually identical, but the 14 lacks the reverse torque mechanism because I guess they felt that the loop formed when going into pause mode at the highest speed on that machine (3 3/4 ips) is not worth worrying about. So all the back tension on the 14 must come from the pressure pad (save for a little 'drag' from the supply reel and friction at the left hand guide post), in contrast to the 15.

Of course all the 70s machines (2000, 3000X, etc) all have the 7 1/2 ips speed and hence the reverse torque mechanism.

Sorry, got a bit far away from the original topic here.

[DOFFERY]

Hi Ricard ,yes we do seem to have drifted away a little from Scotties many problems, however all service engineers will know of the "compromise" situation, against the manual details when all parts are perfect & the service of used machines. Sometimes I have shuddered at some of the DIY situations I have found myself in , but if it works!!!!!

Scottie you stated that there were no small springs between the "tight disc" & the lower clutch half, hence the tight disc should have two prongs that fit into the lower clutch half, the spring being underneath the lower half . you should feel that springiness easily when depressing the reel table . Without one of these two alternative tight disc spring methods the supply reel will not work correctly, just look at the manual .

Colin.

[scottie_UK]

By tight disks do you mean the things with the felt rings on them? If so. Mine are white and have three legs that go into 3 holes on a white disk that the belt is fitted to.. I do remember them being springy, but I'll double check when I'm home.

[DOFFERY]

That's the one Scottie, a later version of the tight fit unit.

Belt in the post.

Colin.

[scottie_UK]

Right then, belt received and fitted. The rewind and fast forward are now excellent and it plays smoothly too. Also the issues with the erase head appear to have vanished too. Result!

However, the problem with the gravelly recoding sound quality remains.

Right I have a digital multimeter that allows me to measure DC volts, AC volts, DC Amps, AC Amps, Ohms and continuity.

The service manual for the series 2000 does not seem to provide information on where to test and what to look for, so I will need your guidance folks.

[ricard]

So it seems to be erasing fine now, no trace of the previous recording?

Is there a way you can record a snippet of what it sounds like to a computer and post the file somewhere so we can listen to it? It would help to hear exactly what it sounds like?

[scottie_UK]

Originally Posted by ricard

So it seems to be erasing fine now, no trace of the previous recording?

Is there a way you can record a snippet of what it sounds like to a computer and post the file somewhere so we can listen to it? It would help to hear exactly what it sounds like?

Well, it erases all of what it records, however there are very very small remnents of a recording made on another non stereo multi track machine years ago. These can only be heard if I turn the sound way up and remain (I expect) because the head alignments may have been different in that machine (a Grundig TK of some sort).

I will record the sound and post it up in an hour or two.

[DOFFERY]

To measure the erase voltage , across the head itself 90/110 volts., each segment, When testing for track alignment always use a blank tape, not one recorded on a different machine of unknown quality.

Colin.

[scottie_UK]

Whilst testing and fixing the break I have come accross another problem. I'm having an this time with the joystick, due most probably to the gunk (dried up grease). Pressing down to play on the joystick involves considerable effort. This makes the back ball of the joystick jump out of its holder, about 20% of the time.

I tried to loosen the mechenisms with sewing machine oil a few weeks ago, but it has had little effect. Any tips.

[scottie_UK]

Ok so I think I now have an accurate mental model of how the reel tables work and as a result have them running near perfect. Its very difficult to get the width of the friction pads, and the friction levels just right when using a leather belt. After three attempts I got something that is workable. I get the reverse friction from the supply spool during play and it rewinds speedily.

The joystick issue appears to be one of oil and gunk, and after a further oiling, seems to be a little better.

As for the sound it has not improved and the left channel still does not record unless I gently press my finger on the supply spool, press the felt pad or the tape against the record head. This says its an issue of tape tension.

The sound however is still gravelly in both channels. Here is an recording I made this evening. Its in MP3 format to keep the download small, but it should give you a feel for what it sounds like.
http://dl.dropbox.com/u/30109412/Tan...Test_later.mp3

I'm still half tempted to give up and get a 9041x off T'internet.

[ricard]

Just a quick analysis as I've just listened to the recording a couple of times on my laptop and not phones.

You said you'd recorded a sine wave from your computer. Seems like the frequency is around 130 Hz (or I goofed up my calculations)?

First of all it sounds badly clipped, and there's hardly anything on the left hand channel. On the right hand channel the character of the sound seems to change, for a few seconds it just sounds like white noise. I'm assuming you didn't do anything, just let it run? So the variation in sound is due to the machine acting up?

There will probably be more opinions, but if I were diagnosing this I'd work my way through the recording amplifier with an oscilloscope or even just a signal tracer (i.e. an amplifier and loudspeaker) to try and zero in on where the fault was. But first I'd check the internal DC supply voltage within the machine to see that it wasn't too low, as that could cause all sorts of problems. I can't remember, it's supposed to be somewhere in the +24V to +27V range I believe (check the service manual).

Also, something struck me when I was rereading previous posts. You wrote that it erases its own recordings perfectly, but not those from other machines. That indicates that the erase and record heads are aligned with each other as far as height goes, but that the playback head is not. I.e. the playback head is picking up the recording of an adjacent track. It should be possible to see from the wear pattern on the head if it's out of alignment.

[scottie_UK]

Originally Posted by ricard

Just a quick analysis as I've just listened to the recording a couple of times on my laptop and not phones.

You said you'd recorded a sine wave from your computer. Seems like the frequency is around 130 Hz (or I goofed up my calculations)?

First of all it sounds badly clipped, and there's hardly anything on the left hand channel. On the right hand channel the character of the sound seems to change, for a few seconds it just sounds like white noise. I'm assuming you didn't do anything, just let it run? So the variation in sound is due to the machine acting up?

Just to let you know in that recording it are Saw Tooth, Pulse, Sine and Whitenoise wave forms (in that order), that play one after the other. A cycle that's repeated twice.

Originally Posted by ricard

There will probably be more opinions, but if I were diagnosing this I'd work my way through the recording amplifier with an oscilloscope or even just a signal tracer (i.e. an amplifier and loudspeaker) to try and zero in on where the fault was. But first I'd check the internal DC supply voltage within the machine to see that it wasn't too low, as that could cause all sorts of problems. I can't remember, it's supposed to be somewhere in the +24V to +27V range I believe (check the service manual).

The service manual does not describe how to do this. Any tips would be greatly received.

Originally Posted by ricard

Also, something struck me when I was rereading previous posts. You wrote that it erases its own recordings perfectly, but not those from other machines. That indicates that the erase and record heads are aligned with each other as far as height goes, but that the playback head is not. I.e. the playback head is picking up the recording of an adjacent track. It should be possible to see from the wear pattern on the head if it's out of alignment.

When I first received the deck it would record and play back its recordings beautifully. I don't want to go messing with the playback heads, as these recordings first made still play back very well.

Andrew.

[ricard]

Originally Posted by scottie_UK

Just to let you know in that recording it are Saw Tooth, Pulse, Sine and Whitenoise wave forms (in that order), that play one after the other. A cycle that's repeated twice.

Ok, well that explains the change of sound then. In that case it doesn't sound clipped; the sine wave is nice and devoid of harmonics as it should be, etc.

It does sound like there are excessive dropouts on the recording though, both short ones, and also over longer periods of time, as the sound drifts in and out. Left channel is much worse. That would tend to point to the tape tension being too low, alternatively the head being maladjusted in the respect that the face of the head is not at right angles to the tape. The latter would be rather unlikely given that no one has tempered with the adjustments though.

Originally Posted by scottie_UK

The service manual does not describe how to do this. Any tips would be greatly received.

Well as I said now knowing what's supposed to be on the tape, it doesn't sound like that is the problem at all. (But basically, signal tracing involves tracking the signal through the amplifier, by simply touching the input and output of each amplifier stage with the probe and verifying that the signal is there and in most cases larger at the output of each stage. It's a standard fault finding technique so probably wouldn't be described in an individual service manual.)

[scottie_UK]

Ok so I had my TestLab multimeter set to AC volts and measured each channel of the erase head and record heads. Here are the results

Test Results

Test Conditions:

• Saw wave (C on 8') into both L and R channels via line input (DIN socket) generated by my computer.
• Both record channels set on tape deck so signal coming in reads -2db.
• When getting the above results both the left right record volume knobs are at the same stetting which is about 1.8.
• Recording on both channels.
• Playing on both channels set to tape.
• Tape speed 7 1/2.
• Multi Meter set to AC volts.

Record Head:
Tried various settings until I got a reading. Started at 200m, then 2, then 20 where I got the reading. Before this setting the multimeter would output 1.

• Top Pair at setting of 20: 0.18
• Bottom Pair at setting of 20: 0.68

Erase Head
Tried various settings untill I got a reading. Started at 200m, then 2, then 20, 200 and finally 700 where I got the reading. Before this setting the multimeter would output 1.

• Top Pair at a setting of 700: 640 (note not 0.640 there was no decimal point showing)
• Bottom Pair at a setting of 700: 641 (not not 0.641 there was no decimal point showing).

End of Tests

So what could these values evidence? The erase head voltage surprises me. When I corrected the wires I saw no sparks (well actually a v small one once, but no more than you would get of a 9v battery).

[scottie_UK]

Here also is part the recording made when doing the test. Notce the left channel is considderably quieter. It also drops in and out and it does not matter if the supply spool is near full, halfway full or near empty. It just does comes in for a while then goes out (but not completely).

http://dl.dropbox.com/u/30109412/Tan...ageTesting.wav


Also tried RS equivalent of Kontact 60 cleaner, no better.