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..

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)