Tandberg 2041 (series 2000) Erase Head Problem.

[DOFFERY]

Sorry Scottie but you are getting far too involved in my opinion, you really need some hands on help. The readings you give bear no relation to the actual readings you should have, albeit the record figures show a large variation, whereas the erase figures are at least balanced.

I confess that having to go back over the many previous posts to see where you are in the process, is getting a bit involved.

Can you go back & start again with the normal procedure assuming your mechanical set up is OK? A known well pre recorded tape (not one you recorded on this machine originally)to check the playback first, check the voltage as Ricard suggested, then we can go into the record sequence, the sound of music would be of greater benefit than the tone.

Hope you accept the comments as given , in an effort to assist.

Colin.

[scottie_UK]

Ok. I'll have a go tonight.

I get involved because I am keen to learn and keen to get it right.

[ricard]

Originally Posted by scottie_UK

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

From what I can tell the TestLab range looks like a fairly standard multimeter. Being so, they are primarily intended for measuring 50 or 60 Hz AC on the AC range. The measurements might be useful up to a couple of hundred Hz, but I wouldn't trust the readings in the frequency range of the bias frequency of a tape recorder - 85 kHz or more for Tandberg.

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.

Normally one would start at the highest range and work one's way down if the value were small. Doing it the other way could damage the instrument, although I would think that a modern digital multimeter would have ample protection.

The "1." reading indicates overrange, i.e. that the measured value is to large to display on the selected range.

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

The actual value doesn't make sense, but as Colin noted, it is not the same between the channels.

• 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).

This really shows that the values are far off. A value of 640 would mean 640 volts which is far too much - it should be around 100 V as Colin mentioned, but it's probably caused by the bias frequencey leaking through the input attenuator on the instrument. Again, as Colin noticed, the values at least are balanced.

Given this, the values on the record head seem odd, 0.18 and 0.68. On the other hand, I wouldn't count on the instrument reading correct values anyway, so the attenuation factor set by the range knob probably isn't accurate at the bias frequency.

[ricard]

Originally Posted by scottie_UK

Here also is part the recording made when doing the test. Notce the left channel is considerably 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).

This one sounds better than the previous test; the left hand channel is not as low as on that one.

The voltage you read off the record head would indicate that there is a disproportionately large difference between the bias levels for the two sections of the head. Listening to the recording, the left hand channel sounds muffled, but it's difficult to know if that's due to bad head contact at the playback head, or too high a bias level. Since the voltage on the left (top) half of the record head is lower, that would indicate that the bias is too low. If you can locate the bias trimmers you could try adjusting the left hand channel and see if if makes a difference in playback signal level. Remember what the trimmer was set at to start with so you can get back if you don't get an improvement.

Since you've got a three-head machine you can do the adjustment while the tape is running, on a two-head machine you'd have to make a recording, wind back, etc.

The fact that the signal level varies indicates to me that either the tape is very used and hence dusty (the variation in level is caused by dust adhering to the recording head, then moving on after a while), or the tape tension is too low to maintain good tape-to-head contact.

To set the bias level properly, you could set up your PC software to generate 1 kHz and 10 kHz sinewave signal alternately. Record the resulting signal, and adjust the bias trimpot until the tape plays back the same level for both frequencies. If the 10 kHz is too low, decrease the bias. If the 10 kHz is too high, increase the bias. The important thing here is to get a balance between the too, if the level is wrong, that has to be dealt with somewhere else.

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

Ok, well good to rule that out then.

As Colin is getting at, it helps to try and check the playback with a known good tape, to verify the playback levels are correct, before moving on to record.

[scottie_UK]

Ok I've run various tapes though the deck in playback mode. These were recorded on other tape decks. The sound played back is excellent and is as good as it was when I received the machine.

So lets give a summary of what has happened so far:

The thing about this deck is when I got it. It sounded so good I made a video of it. I have a great recording of The Sound of Philidephia by MFSB (disco with orchestral strings) . It recorded well, played back well, but had rewind and fast forward speed issues due to a stretched belt, and rotten spool table pads (it still worked and I could live with the faults). I've played back this original recording again and notice now that a bit of the previous track remains underneath the left chanel (owing most probably to tape tension issues preventing complete erasure).

After two weeks of ownership one night the left channel suddenly dropped considderably (erasure and record) out during recording and its never been the same since. After reading the service manual and trying head alignment (because pressing the tape against the record head seemed to work). However, now I know these issues were due to the tape tension and I should never have messed with the alignment of the erase and record heads. That said I believe I have set them to be set back as they were (or at lease close).

I then worked on making DIY replacement pads, these are in place and seems to work well with supply reel giving back tension during playback, speedy rewind and FF with no slippage, excellent playback of rerecorded sounds but the recording is still off.

[DOFFERY]

Sorry I had to be brief this morning Scottie but I had to get to work. However Ricard has gone over the points I would have made re. the recording. If you can locate
the preset R511 on the main board, you have the circuit, this is the bias preset for Right ch. Do as Ricard suggests on B test either with a tone or music, the latter would be simpler to start with, adjust & see if it makes any difference, if so you can then use the tones to finally adjust. I suggest the right ch. as this appears to be more suitable to give you the best results, the left ch. can be adjusted later.

Looking again at the figures you gave , on the erase if we move the decimal point we get 64 volts, should be 90 at least. For the bias, if we again move the decimal point we get 1.8volts for the left ch. very low, the right one 6.8 rather high but in the right area(should be 5/6volts) As mentioned we have to allow for the type of meter you are using, again if possible use a blank tape for this record/bias test

Colin

[scottie_UK]

Before I go poking arround with the Bias. I did a little test this evening. I connected the modern stereo ear pieces to the both pairs of connectors in the back of the record head. The sound coming though the ear pieces was crystal clear, and without any distortion. Also the volume from both sides seemed well balanced.

I also want to thank you both for putting the time end effort into asisting me on this long road to reel to reel bliss.

BTW If this does not work out I'm thinking of buying a 9041x. Would this be a worthwhile investment?

[ricard]

Listening to the recording signal as you've done will give a good indication of state of the recording amplifier, however, the actual signal recorded on tape is heavily dependent on the presence and level of the high-frequency bias signal. So we can rule out any problem with the recording amplifier, but it could still be a bias issue that causes the low signal level.

My two cents worth would be this: if the signal level drops suddenly it can be due to a small speck of dust getting caught on the face of the head. If it happens at the recording head, the level will simply drop. If it happens at the playback head the most noticeable effect is that the treble drops (even though the signal level can also drop depending on the size of the dust). With worn heads it tends to happen more, due to the head surface being more uneven, and especially on the left channel, where the edge of the groove caused by head wear makes it easier for dirt and dust to grab hold. Polishing the heads can help, but should be left to professionals. Just cleaning the head (even with a dry Q-tip) causes the dust to go away of course, but sooner or later it happens again.

Regarding the 9041X, I've had the successor 9141X for thirty years, and it's been a great machine. The mechanics seem really stable and well designed. I've had few issues with mine, the most serious one was a fault in one of the logic chips which was awkward to fix as they're obsolete by now so I had to fudge something using modern-day chips. Other problems have been the grease in the tension arms hardening, and it needs to be replaced by some sort of hard-to-find damping grease to work properly. A transistor driving the VU meter lamps eventually failed due to poor design of the drive circuit but was easily fixed. I've been led to believe that the 9000 has some deficiencies compared to the 9100, so the latter is a better choice, if you have the choice.

All said though, the machine will be of similar vintage as your 2000 so there could very well be similar issues with head wear, or with brake bands needing replacement, dodgy internal connectors, or something else typical of a machine 35 years old. Still, the three-motor design seems to be more robust than the single-motor mechanically controlled 2000.

[scottie_UK]

Some really good news. I took of the wooden facia of the deck. I did this a few weeks ago also soon before the problems started.


Soon as I took it off the problems with the recording largely disapeared. I'm thinking a screw was a little tight and may have touched the circuit board. Its the only plausible explanation I can find. All the screws are the same size so its not a problem of ordering. I've put the wooden surround back on and now the problems with the heads have gone.

Anyway, we are 90% of the way there now. Just one small problem, the back tension on the supply table is uneven and as a result causes a warble in the sound (not the drop outs as before).

It seems the cause is my DIY leather friction pads. They are not quite thick enough and thus they rub against the white pulleys slightly making them not run smoothly. Were almost there.

[ricard]

I wouldn't think that a casing screw could be tightened too much so at to short-circuit something, but it could cause something to bend, exposing a bad connection or a crack in one of the circuit boards.

Nice to hear the machine is working fine again.

Regarding the friction pads, Lasse Hovde in Norway makes replacement parts (see the top of this page: http://www.nrhf.no/kjop-salg/repdeler.html ). A set of six friction pads cost NOK 100:- or about £10 or so, plus postage. I ordered a set for my 4000X and was very pleased with the results. Saved me the need to try and get some sort of DIY pads the same height.

[DOFFERY]

Scottie.
Glad you have located the problem & all is now well, it just goes to show that even service engineers overlook these matters or take for granted initial sales insructions were followed.
When these machines were sold they were supplied with a pair of screws & an explanatory note regarding the fitting of same relating to such problems. There is a note in the manual somewhere relating to the reasons for the screws.

Ricard is quite right about the new pads, they are or were excellent, I don't know if they are still with us, however a good wine cork slit to the correct width & halved(shape not essential) is a good stand by. Congrats for sticking with it.

Colin.

[scottie_UK]

What about cork pads from the DIY store cut to approx shape?

http://www.inest.co.uk/images/L30182.jpg

[DOFFERY]

By all means Scottie, there are many & varied DIY means of replacing the pads.

Re. your latest problem ie. the screws, look at the first page in the manual "General Information" bottom of the page!!!!

Colin.

[DOFFERY]

Just a query Ricard, are you Ricard Wonderluf (apologies if incorrect) ? If so I think we have something in common?

Colin.

[scottie_UK]

Originally Posted by DOFFERY

By all means Scottie, there are many & varied DIY means of replacing the pads.

Re. your latest problem ie. the screws, look at the first page in the manual "General Information" bottom of the page!!!!

Colin.

Yes I read that but thought it was referring to special extra long screws for mounting the legs. Obviously it isn't. Doh.

Incidentally, I pulled out one of the crumbling corks from the bin to look at its thickness. It would seem my leather belt is spot on for thickness. However, I beleive what is causing the warbling is the white pulley beneath the table. The one of the left does not seem to run completely true, wobbling slightly. Which is obviously being transferred to the tape tension a little.

When I run it with no pads it ran and sounded fine. I am reluctant to buy pads from Norway if my solution is AOK and the problem lies elsewhere.

[scottie_UK]

I've played about with various settings and now do believe I may have it.

[scottie_UK]

Nope. But it back together and erase heads not working well on ether channel, but recording and playback excellent.

[DOFFERY]

Scottie,
Re. the warble & uneven LH table, sometimes the "tight" pulley needs to be rotated as the individual pegs & holes do not relate correctly , one position will be OK. Also ensure whichever pads you fit do not make contact with the tight pulley. There are a set of 5 tools which you may or may not be aware of ,3 of which enable the turntables to be aligned correctly, mis alignment of the left turntable may be your problem re. the warble.

Colin.

[DOFFERY]

Not suggesting you invest in the tools(if still available) but the attached will give you some idea of the alignment process. If not clear enough e mail me & will forward a better pic.

Colin.

[ricard]

Originally Posted by scottie_UK

However, I beleive what is causing the warbling is the white pulley beneath the table. The one of the left does not seem to run completely true, wobbling slightly. Which is obviously being transferred to the tape tension a little.

When I run it with no pads it ran and sounded fine. I am reluctant to buy pads from Norway if my solution is AOK and the problem lies elsewhere.

My experience has been that sometimes the white pulleys can tend to warp with time. Don't know if it's just attributed to age, or heat or other issues can make it worse. It's not usually a problem unless they get really bad.

I'm a bit confused though, the pads should normally not be touching the pulley when the machine is not winding backward or in stop mode. Isn't there a separate felt pad located centrally providing the back tension (or am I confusing the machine with an earlier model?). I thought the "three pads" only provided torque in wind mode (and are also engaged in stop mode).