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technics 1200 technical issues

Hi!

This is about modifying a technics 1200 MK2.

I guess I've read all of the tutorials that are available but there are two things that i'm curious about :

1) When adjusting the pitch range one would play with the vr302 (that one) until it's around 2,7kOhm for the stock settings.

But if I wanted to have a range of lets say 4% instead of 8%? I tried adjusting the resistance value (lowering it) but that would give me some pretty unpredictable results, the positive range gets widened but the negative range stays the same for example, what would the correct value be?


2) My other deck is broke. It will randomly (very seldom though, probably once every 5 using hours or so) start shifting the pitch up and down randomly for about 30 seconds to one minute. Usually I can switch it off a few times and plug it in&out and it will be normal again, but obviously it cant be used for live playing.

I have absolutely no idea what could be the problem here, the pitch fader has been replaced but to no use. I've just now switched the entire pitch assembly (fader + PCB board) with my other deck to see whether it's the PCB board or something more vital (the motor..)

any ideas?? does someone know a good page for technics 1200 repair?

thanks guys

I wouldn't mess with anything on your decks

I would go to a store that repairs them and find out wtf is wrong.

Did you check to see if there was like soda or anything split inside? I know when I scraped soda off my boards and my pitch fader, it worked a charm and stoped jumping back and fourth from -8 to +8

heh no, there's no soda in it

the thing with stores is that they're kinda expensive, hard to find (I live in a 3rd world country) and I'm pretty confident that I'll be able to do the work myself too (soldering and that stuff)

so i was hoping that someone had similar problems + solution.. or at least an indication which part could be the culprit.. since it's such an odd thing and happens so seldomly i wonder if i bring it to a store they'll even notice it..

Re: technics 1200 technical issues

quote:

Originally posted by gzf Hi! This is about modifying a technics 1200 MK2. I guess I've read all of the tutorials that are available but there are two things that i'm curious about : 1) When adjusting the pitch range one would play with the vr302 (that one) until it's around 2,7kOhm for the stock settings. But if I wanted to have a range of lets say 4% instead of 8%? I tried adjusting the resistance value (lowering it) but that would give me some pretty unpredictable results, the positive range gets widened but the negative range stays the same for example, what would the correct value be? 2) My other deck is broke. It will randomly (very seldom though, probably once every 5 using hours or so) start shifting the pitch up and down randomly for about 30 seconds to one minute. Usually I can switch it off a few times and plug it in&out and it will be normal again, but obviously it cant be used for live playing. I have absolutely no idea what could be the problem here, the pitch fader has been replaced but to no use. I've just now switched the entire pitch assembly (fader + PCB board) with my other deck to see whether it's the PCB board or something more vital (the motor..) any ideas?? does someone know a good page for technics 1200 repair? thanks guys

The best way to adjust the pitch is trial and error, I've taken mine from stock settings to about +/- 14 and then back and sometimes even less than stock settings. The only thing you'll have to worry about is having two "zero" spots because when you click at zero it bypasses the slider to the quartz lock and the other zero somewhere else. If that happens adjust the pot on the fader. Or, you could even get rid of the click if you wanted.

These decks are meant to be toyed with (if you know what you are doing) that's why they can last for so long and yeah.

The second thing, two scenarios come to mind with the info you posted.
A: Power supply/motor, let a tech deal with that.

B: If you've replaced the fader, it shouldn't be it but try this

Try and narrow down when it's going all crazy.
is the quartz lock on?
is it on 33 or 45?
and so on

The best thing to do before going and replacing a bunch of stuff though is trying to find the route of the problem.

i have removed the quartz lock so that's not a problem... but trial&error sounds tedious.... especially with the deck lying half open and you having to turn it around and plug it in and out for each trial.

but oh well when i have lots n lots of time I'll try it for now i stick to stock

regarding the other one its the same whether 33 or 45 or anything. the only thing that I thought was a giveaway for power failure is the stroboscope light getting dimmer and flickering around but i think its connected to and adjusts witch the pitch so that doesn't help(since it changes when you switch from 33 to 45)

What caused this to occur ie did you make some modifications to the unit like a new LED kit etc? I was told the LED kit on e-bay has a dodgy connection and can cause a short. If that is the case the strobe does 'flash' bright/dim. Do you have a multimeter?

well there was nothing, really.. it just started gradually, at first i thought it had to do with the power cord because plugging it in and out usually helped but then it happened more often and was harder to fix (ie plugging out for several times, playing with the 33rpm 45rpm knobs...)

there were no special modifications that i did that made it stopped working, the only thing i did was the fix for the pitch fader but the first occurrence was long after that

quote:

I have absolutely no idea what could be the problem here, the pitch fader has been replaced but to no use. I've just now switched the entire pitch assembly (fader + PCB board) with my other deck to see whether it's the PCB board or something more vital (the motor..)

has this made any noticable difference?

I'm not really sure I understand what is occuring. Is it that the speed of the platter is inconsistant? I find it odd that when this occurs it is only occassional. Does the strobe light dim wehn you press the start/stop button or only when the speed alters?

Assuming you have a multimeter, On the main board next to where the power attaches there is a big blue capacitor. Looking at the board with this cap on the bottom left, you will see a diode (long black bit that is standing on 4 posts in a straight line) that runs in the same direction as the big cap almost touching it. At the end of the diode is written in text on the pcb D1. Right next to that is a line which seperates D1 from [in my case] D3 - this should actually read D2 as that is what is on the schematic so I'm not sure if panasonic ever had it updated.
You can follow the line to an arrow with a box that shows 5V. Other end of the line is the point at which you connect the positive of the multimeter, set to measure the voltage and the connect the negative to a neg on the pbc (I use the post on the other side of the 'motor' marked G for ground - you'll find it next to where PITCH is printed on the pcb) . This point should measure 5 volts.

If it does not, you can change this diode out with a new one (Use a 5.1 Volt Zener diode noting which end is marked with the ring). Tho this won't be casuing the problem, it may be contributing.
Next, you also need to change the transistors Q2 Q3 which are tucked under the silver guard for the motor about an inch from the big capacitor. it's hard enough to measure them to see if they work, so I'd change them both together. You can order them through Panasonic service center for about $5 Aus each - check you local dealer via panasonic official website. The part number for these is 2SD637.


After all that, I cannot be sure that this will fix the problem. I have heard that it could be caused by a fault in the IC's also, but as they can cost up to $25US I'd try the other first and see how it goes. Just be careful how much heat you apply with the soldering iron. You don't want to stuff the new transistor before you even try them out.

Of course if the zener measures 5V like it is meant to, I have no fukin idea

hey! first of all thanks for your extensive reply

yeah it's only occasional, and it doesn't last very long!

I can't test it on the deck right now since it's still open but one thing i do remember is that the strobe light flickered at almost every major change of pitch (not only when i change the pitch setting from 33 to 45, but also when I touch the platter itself and speed it up or slow it down)

I used to think this was normal but it doesn't happen on my good deck. and on the other one it was very noticeable, so that might give a clue.

regarding the 5v check, i did find everything but in order to get a voltage reading I'd have to plug it in & turn it on, right? I remember reading somewhere that turning on the deck without platter on = very bad karma (and a broken deck)

ps: i did try the reading anyways but it gave 0v (i didn't know which one of the red&black cables is which polarity so i tried both :P )

The unit does need to be plugged in to test the voltage reading, just be aware that the mains power is exposed by taking off the black plastic vented cover (from the transformer to the little board left of the blue capacitor) - it's actually a poor design. What ever you do, don't go poking around with your fingers if you value the use of oxygen).

As for damage to the unit by turning it on without the platter, well I've not experienced this. The warning on the unit says not to do it but that may be for the mains exposure issue. Certainly by doing it for short times has no effect, perhaps extended periods may cause some issue??

When you say at change of pitch, do you mean by altering the pitch slider anywhere between -8 and +8, or only 33rpm and 45rpm.

When the strobe flickers, does the platter the record sits on change in speed? ie kind of jump around faster and slower instead of just maintain constant rotation if settings are not altered?

One of my decks had this issue, and by changing the transistor I mentioned, it fixed the jumping about in rotation speed, but there is still an ongoing issue that occurs when the deck is set to rotate by pressing on/off button, where the strobe still dims. The circuit is measuring 11 volts insted of 20 at some points, and I'm still working on finding the problem. It seems as though one of the capacitors may be blown, but I can't yet find which one, and when I finally put the time into it, I'll probably swap them out, one by one untill I find the culprit. It's a pain in the ass really. I am in the process of modifying the deck with painting etc, but have been a bit slack (started 6 months ago, but now the weather is getting warmer here I'll probably get it done soon) As the unit is in pieces, I'm not sure what problem the current issue is doing, but I think it just causes the record to start slower than it should, and that's all. Have to wait till I get it back together before I find out.

quote:

Originally posted by skot_e As for damage to the unit by turning it on without the platter, well I've not experienced this. The warning on the unit says not to do it but that may be for the mains exposure issue. Certainly by doing it for short times has no effect, perhaps extended periods may cause some issue??

i think it's because when you start the motor without platter on it's gonna burn since it has no weight on it. (or something along those lines)

so as long as i dont accidentally hit the start button, i should be fine right??

I'm gonna give it a try later today

Well the thing is, by pressing the start button, all the 'motor' does is create an electro magnetic field, which causes the platter to rotate. They are not electically connected in any way, and so there is little chance of a problem. The only thing I can think of is that the switching on or off when it induces the magnetic field will have a feedback type of issue where the polarity of the motor should change slower but doesn't because there is no resistance in the magnetic field. I'm not really 100% on this opperation tho, all I can tell you is that in 13yrs my decks have never suffered by switching it on with the platter removed.

But like i said, be careful of the mains power. It can't be understated how dangerous the unit is when the black plastic cover is removed and the electricity is still connected. The wires that carry the 110V are exposed. (Even for 240V mains there is a stepdown transformer which puts out 110V to the circuit board)

quote:

Originally posted by skot_e The unit does need to be plugged in to test the voltage reading, just be aware that the mains power is exposed by taking off the black plastic vented cover (from the transformer to the little board left of the blue capacitor) - it's actually a poor design. What ever you do, don't go poking around with your fingers if you value the use of oxygen).

Sorry for the off-topic response, but this is very true! I shocked myself HARD doing this once.

Lucky it wasn't worse...

hi! sorry that i didnt answer in a while, but i had a thing (exams actually)

well the reading is 4,86V. is that still in range?

for one i'm pretty sure that the error is definitely not caused by the pitch control unit, i switched it to my other deck and that one still works fine, plus the last time the faulty deck was behaving strange i plugged out the cable leading to the pitch and it would still speed up and down randomly in the same manner (the usual thing what happens if you pull out the cable is that it speeds up and down very symmetrically)

also, when touching the platter i could feel a force that is pushing it forward or backward

and the strobe light starts flickering whenever I touch the platter and move it forwards or backwards by hand, which is weird (this happens all the time when the deck behaves strange but it happens also when it runs fine but i move the platter by hand)

when replacing the diodes i would have to remove the circuit board they're on and stick on the new diodes and solder them on the back of the board, right?? can u remove the board easily?

well another thing is, when i was putting the pitch control back in I decided to make it a bit smoother and put in some grease and it didnt get any better so I tried other things but none worked, i realized that the not smoothness came from the electrical contacts producing friction (and not the upper part of the slider where i had put in the grease) since they were pushed pretty much together so i did some other things which led to the contacts being farther apart from each other so it went smoother, the downside is that now every time i push the slider in a certain way the contacts won't touch at all thus making the pitch go crazy

is there something you could put on the contact slider to make it go smoother??

Go easy on me if I get a bit all over the place, I just got home from working untill 5am (shooting a short film set at night).

If the reading on the didode is 4.8 V it may be that the transistor 2sd637 is ok (and the diode tho it should read 5.1 or 5? not really sure what sort of tolerance it should have), I have a feeling that when I blew my transistor, it casued a fault with the diode - ie the problem was related. By the sound of it, you problem is different to mine anyway, as my strobe would filcker when ever I set the patter in motion, and not randomly, and not by touching it with my finger. It is a strange issue indeed. It seems more like something may be lose as opposed to being broken, but with electronics, who knows.
One thin you can try is to remove the IC's (compter chips) from the good board, and swap them with the dodgy board and see if one of them is faulty. It's not har, but it is a process of elimination. I was actually told to try this to solve my problem by a tech, but it didn't help me, and that's when I looked into other things. There are 3 to try and swap, and using the blue cap as a starting point:

IC 301- Top right,
IC 302 - next to it
IC 201 - bottom right - the one with Technics printed on it.
If it proves to be one of those, you can order them on the net, or from a dealer - I'll get part numbers later if needed.

In answer to how to work on the board, disconnect the mains, unplug the three wire looms that are around the edge, then there are just tree screws to take out, and cut the zip ties and you can lift the boar partly out. It will still be connceted to the power board,so I just fold it over and work on it that way. I don't have the tools to dis assemble the wire wrap attached to the posts from the power supply board. Then, using a solder sucker and soldering iron, desolder the chips (only do one then swap it over and try it - it really would help if you can recreate the problem with intent). if you can solve the issue with this method, then you just need to replace the chip with a new one.

This is really the only other option I can give with my knowledge. if that doesn't work, you may need to send the board away for repair - google the turtable factory - I think that's their name. I've seen lots of posts elsewhere saying to send stuff to them. It would mean disconnecting those wire warps I spoke of, but it saves freight cost on the whole deck.

Part II
Pitch fader

read this first

http://www.tranceaddict.com/forums/...scratchy+faders

I'm going to bed for now, but I'll answer any questions you might have after you read that thread

first of all thanks again for your reply but man that is going to be a huge operation

i'm really scared to replace the parts with my good deck since unlike the broken one, where it doesn't matter if I try to fix it myself and brake something accidentally, I could in the worst case end up with no deck at all

i'm definitely gonna have to think this through..

regarding the fader, i read the thread but it really doesn't apply to my case, it's something really specific to the technics 1200 mk2 pitch fader.

the question would be which places you'd have to lube in order to make it run smoothly or in a more general way, what are the factors that can make it have bumps (positions where it offers more resistance than in other places)

when I opened it up I noticed that it hat some sort of rubber inlay that would fill the gap where the slider is in, and in some places that inlay was narrower than others so I tried to make it wider - next i thought it would be the outer walls which where somehow bent in in places so i tried to make them even and of course I put grease everywhere but the actual contacts.

when i put it all back together and tried it out it still wasn't very smooth and i looked at it from the side and it looked like the contacts of the slider where pushed really hard to the contact board, thus creating a lot of friction between the two. what I stupidly did then was to change the slider (removing part of the upper structure) so that the contacts would be further apart, but now they are so loose that they don't make any contact at all sometimes.

what I think now is that maybe the rubber inlays do offer a certain resistance which is higher than the friction produced by the contacts which is why you have to apply more force to move the slider to begin with but it still is continuous, and in widening the rubber inlays I killed that bigger resistance which is why the friction between the contacts is now more noticeable. (does that even make sense??)

aw well at least i have one good deck left

Sounds like you already attempted to pull the fader appart (ie strip it into it's seperate pices) Is that right? When I pulled my fader appart, there was very little lube in there, more like a tiny amount of oil which had become clogged with debris over the years and therefore needed some cleaning. The reason I referred you to the other thread was because I was unsure if you knoew the component make up of the fader. The 1200 fader is the same as the one in the thread, with only very slight differences. Functionally they are the same.

I'm not sure of the rubber inlay you are refering to - are you able to take and post photo's?. The internals of the fader (mine) are a piece of plastic, and the metal shaft that runs through it which the slider button/cap/knob thing fits on. There is a very thin piece of material which is only a dust trap that runs the length of the fader, and a ring of material which does the same thing under the slider knob. My fader moves smoothly, before it had the centre click, but I removed that when doing cleaning (quite easy). Perhaps the centre click is the resistance your refering to??

quote:

when i put it all back together and tried it out it still wasn't very smooth and i looked at it from the side and it looked like the contacts of the slider where pushed really hard to the contact board, thus creating a lot of friction between the two. what I stupidly did then was to change the slider (removing part of the upper structure) so that the contacts would be further apart, but now they are so loose that they don't make any contact at all sometimes.

Can you explain this in more detail. How are you looking at the contact? is the fader stripped to single pieces? I'm wondering if that may be the problem now.
I still need to do the fader on my 2nd deck, so when I get my camera, I'll do that like I did the other fader thread. It might help, but it won't be for a while yet.


As for the chip's being swapped, if your unsure, maybe get a local technician to do it, but if you have done soldering/desoldering it is a very simple task. Just be sure to put them in the same way they came out and your good to go. And don't over heat the chips.

Here's an image I found of one dismantled to give you an idea if you not sure

yeah, mine is different. it doesn't have the spring and it has a rubber inlay. plus it doesnt have any pins anymore since I broke them. (material failure I say, the second time I bent them they broke)

it does have 4 long pins though, that are soldered to the pcb board but don't do any electrical contact (this is I believe the older design but I'm not so sure)

no matter, I'll try to get a camera this weekend and take some pictures to make this clearer.

bye

Not sure if you mentioned it already,but what model do you have, ie mk2, mk3,etc?
The spring in the plastic also has a ball bearing and that is what creates the centre click position. removing it just allows a smoother slide, but the quatrz lock still works meaning you still have an inaccurate point around the zero mark. This can be disabled, but I'm yet to do it to see what it is like. There seems to be two methods for this, one of which seems a bit dodgy electronically.
So did you buy these new or 2nd? Did it look like someone else had done some work on the pitch slider befroe - ie desoldered it or anything?

I'm wondering if those broken pins may have caused the problem, or was it already faulty when you dismantled the thing the first time.

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