Ghost in my DD33?

No unfortunately my Walkman isnt cursed or haunted by the spirit of its previous owner, but I’ve encountered a rather unusual and very perplexing issue with it just in the last couple days. It was working completely fine one day, and the next day the thing was struggling to make the head make contact with the tape, running slow, not to mention wow and flutter all over the place. But it doesnt stop there, after pressing the stop button and the operation light switches off, the motor kicks up and the unit starts working! The only way to stop it from draining its batteries is by removing them. I took the thing apart right after and nothing struck me as being unusual. The center gear cracked which became a whole other problem, but even after a complete disassembly down to the gear arm, i was not closer to figuring out to what was causing this seemingly paranormal issue. I checked the grease and other areas which i suspected could cause the speed fluctuations, however the lubricants were all still there and oily as it had only been serviced last year. I examined the operation switch near the FG Coil to see if it was having contact issues, but to the best of my understanding that wasn't the case. I dug on the Internet for quite a while trying to source other similar incidents, but theres nothing. Im honestly at a loss for words as to what may be causing this. My gut feeling says it could be capacitors or maybe an IC but thats just my helpless guess. I appreciate any comments or suggestions and ill provide some photos if itd help.

 

Does the unit work perfectly when you press the stop button ?

 

No, since the switch doesnt send a signal, the head doesnt receive any power and none of the electronic controls work (Mega bass, dolby, tape type, volume)

 

The wow and flutter and the mechanism struggling to engage the head into position can be realted to the broken center gear, depending on how bad it is. Please put a picture of the mechanism to see the condition of the gear.

 

Significant, its roughly a little less than half a centimeter and i would agree that a crack of its magnitude is responsible for the poor head engagement. Im going to order a replacement gear but obviously only when i know whether or not this thing can be fixed.

 

Ok, so let me know if I understood your problem correctly: besides the problem with head engagement and high wow and flutter, there is a problem where the motor runs even when powered off ?

 

Yep thats basically it

 

I would check Q607 (motor drive), as the emitter of the transistor is connected directly to the positive rail (as is the servo IC) and a short circuit would cause the motor to run continuosly.
Did the unit get accidentaly powered with reversed polarity before this erratic behavior started to happen ?

Here is a link to the service manual in case you don't already have it: https://elektrotanya.com/sony_wm-dd33_sm.pdf/download.html

 

Crap i think you’re right. I just asked around the house and my late sister said she did. Apparently she plugged it in to a dc power supply we got plugged into a wall in the living room. But we don’t have any center negative power supplies so the plug was a more standard center positive. That must be it then?

 

This is clearly realted to your symptom. What intrigued me is the similarity between this servo circuit (using CXA1423N IC) and the DD3 and D6C circuit which uses CX20084 IC.
In the D6C, this is a well known problem, which symptoms are very similar to yours: motor runs when unit is powered off, when on runs at incorrect speed, etc.
Also the PLL IC (MSM5841MSK) can go bad due to reverse polarity, causing speed fluctuations. So, in reality all the faults can be related to just the fact that it was powered with reversed polarity.

I would check the voltages at IC601 (it could be still good), the transistor Q607 and the waveform at pin 1 and 5 of IC602 to see if it's there and if it's stable.
Maybe you are lucky and it's not the IC601, as unlike the CX20084, cannot be found (which could mean it doesn't fry that often, so it's not a demand for it).

Good luck with the repair !

 

Wow thank you so much! Unfortunately I'm away at the moment so i don’t have it with me, but ill be back by Thursday and i can send an update then. Ill have a look inside and again, thank you very much!

 

Checked IC601 and the transistor Q607 and everything checked out! I dont have an oscilloscope so i cant check the waveform at pin 1&5 on IC602 but im feeling lucky. Im going to order a proper power supply and reverse the polarity here soon, thank you for everything.

 

Glad you are making progress ! Hope that it will work without replacing anything.

IC602 is not critical as it can be bypassed if not working properly (that will increase the wow&flutter). There are 2 pads on the board that can be desoldered (marked on the schematic at pin 5 of the IC).

 

Interesting, i didnt think much about the quartz lock until you mentioned it. But now that you did ill keep it in mind, good to know it can be bypassed by a trimmer (albeit an after market installation) I’ll see if its affected, the power supply arrives tmmr so hopefully all goes well .

 

It's not that it can be bypaseed by a trimmer, the trimmer is already there (RV601 on schematic). It's just that as long as the PLL output ON/OFF tap is soldered, the trimmer will not have any effect. If you desolder the tap (seems to be right above the IC on the board, there are 2 pads soldered together), the speed will be adjusted by just the trimmer.

At least that's how it works in the D6C; but the circuit being extremely similar, I would almost bet that it's the same here.

 

Alright i got the power supply, 3V center-negative, plugged it in and nada I think IC601 must be fried which means (A) I have to source a replacement chip. Or (B) A for-parts DD33 I can salvage the board from. Get back to me if you have any other ideas, your input has been really helpful thus far.

 

I would check the voltages at Q607 first: 3V on the emitter, 2.4V on the base. What is the voltage on the base of the drive transistor ?

 

In play it fluctuates between 1.8v and 2.2v. In standby with the motor running its roughly 1.15v. And in standby without the motor running its 2.65v (The power supply is a little over 3v at 3.2v)

 

Clearly something is not right: the drop across the transistor EB junction should be between 0.6-0.8V. Did the transistor check ok with the diode tester on the multimeter (emitter to base and collector to base) ? it should read around 0.6V
As about the IC itself, if it's CXA1423N, the chances of finding one are slim. And you shouldn't try to source one until you are 100% convinced that is the problem.
That's why I would check that drive transistor first, even try replacing it with another through hole generic PNP just for testing. A transistor failure can also manifest only under load, in which case it will test fine on a multimeter.
It's a 1A 25V with hFE of 200: however, the maximum collector current can be smaller, the motor does not draw more than 100mA. So my guess would be that anything with Ic(max) of at least 200mA will do for just the purpose of testing.

 

Emitter to base is 0.6v and the collector to base it 2-2.2v. Ive sources a replacement chip, seems they’re easy to source since its still being produced by UTC. Havent bought it yet and i wont until you think it might be it