Cannot get Sinewave on my TD125 MKII speed control board

ay · 16th September 2007, 03:33 PM

Hi

My TD125 MKII stop running and I found one of the op amp was not working. I replaced the op amps with two new ones (Old: FU6A7709393 New:LM709CM), I can adjust the voltage to the correct values for all 3 speeds but the motor only vibrates but not turning. So I borrowed a scope from my friend to check out the wave form and find the the wave is some what like the saw teeth on all speed.

I have disconnected the motor and disable the 2nd stage for easy troubleshooting and tried the followings. I still could not get the board to produce a good sinewave! .

1. Replaced the caps at the Wein Bridge.
2. Replaced the transitors tn the first stage.
3. Used one of the old op amp (working one) in the first stage.

I still cannot get a good sine wave produce from the 1st stage with the Wein Bridge. I am running out of ideas. Can anyone help?

By the way, the lamp comes on ok!

Regards,

Alfred

ashok · 16th September 2007, 03:51 PM

"...........the lamp comes on ok.."

Do you mean the oscillator voltage stabilisation lamp ( La1)?

You will find the service manual here :
http://www.vinylengine.com/library_m...ed_model=TD125

The opamps shown are 709's.

MkII is available in english.

Cheers.

ay · 17th September 2007, 12:41 PM

Hi Ashok,

Yes, the oscillator voltage stabilisation lamp ( La1) come on ok. I do have all the services manuals that are available on the internet already.

I need to find out why I am getting the saw tooth type of waveform instead of sine wave. I get the same waveform even when I put the orginal Op Amp (the one still working) back into the circuit. I have run out of idea!

Best regards,

Alfred

Netlist · 17th September 2007, 01:00 PM

C2/C4 broken?

/Hugo

ay · 17th September 2007, 03:01 PM

Hi Hugo,

I have replaced C2/C4 with two new ones (1000uf 63V) and I am getting good voltage reading from both multimeter and osciliscope!

For troubleshooting sake, I focus on the 33rpm portion and I have replaced C12 and C14 with two new 0.1uf already!

Alfred

Netlist · 17th September 2007, 03:31 PM

I whish I could be of more help.
In case like this I try to start from scratch. Confirm every transistor is good and in its proper position, check if the opamps are not reversed in the sockets, everything soldered well, trace the different voltages, measure every resistor, suspect the motor.
I'm pretty sure it's something stupid, constantly overlooked.
Your main question, why the sine wave is a saw-tooth, I can not answer.
I have a TD125 in front of me and I’m willing to measure some voltages but the circuit is not the same as the MKII

Keep us posted.

/Hugo

ay · 17th September 2007, 03:49 PM

Many thanks for your help! I will go back to the basic and check everything again....

Alfred

quadrico · 11th January 2008, 10:18 PM

Alfred - did you get it working? I have a similar problem but cannot source the LM709CMs over the net here in the UK - where did you find them and did you also find the output transistors?

By the way I used to live in Hong Kong - near Sai Kung until 10 years ago. How is the old place?

Brgds,

Quadrico

ay · 12th January 2008, 04:12 AM

Hi quadrico,

So you have a TD125 MKII as well! By the way, I have changed all the caps on the board but I still can get it to work! I do get a sinewave if keep the magnification low. Once turn up the magnification, it sinwave becomes a saw tooth!

Let me know if you need any help to source the op-amp!

ay · 12th January 2008, 04:27 AM

Hi Quadrico,

For the transistors, I am able to get C33725 & C32740 as the replacement. The op-amp I can get LM709CN (14-PIN) and MC1709CP1 (8-PIN).

16th September 2007, 03:33 PM	#1
ay diyAudio Member Join Date: Sep 2007	Cannot get Sinewave on my TD125 MKII speed control board Hi My TD125 MKII stop running and I found one of the op amp was not working. I replaced the op amps with two new ones (Old: FU6A7709393 New:LM709CM), I can adjust the voltage to the correct values for all 3 speeds but the motor only vibrates but not turning. So I borrowed a scope from my friend to check out the wave form and find the the wave is some what like the saw teeth on all speed. I have disconnected the motor and disable the 2nd stage for easy troubleshooting and tried the followings. I still could not get the board to produce a good sinewave! . 1. Replaced the caps at the Wein Bridge. 2. Replaced the transitors tn the first stage. 3. Used one of the old op amp (working one) in the first stage. I still cannot get a good sine wave produce from the 1st stage with the Wein Bridge. I am running out of ideas. Can anyone help? By the way, the lamp comes on ok! Regards, Alfred

16th September 2007, 03:51 PM	#2
ashok diyAudio Member Join Date: Jun 2002 Location: 3RS	"...........the lamp comes on ok.." Do you mean the oscillator voltage stabilisation lamp ( La1)? You will find the service manual here : http://www.vinylengine.com/library_m...ed_model=TD125 The opamps shown are 709's. MkII is available in english. Cheers. __________________ AM

11th January 2008, 10:18 PM	#8
quadrico diyAudio Member Join Date: Jan 2008	Cannot get sinewave on TD125 MKII Alfred - did you get it working? I have a similar problem but cannot source the LM709CMs over the net here in the UK - where did you find them and did you also find the output transistors? By the way I used to live in Hong Kong - near Sai Kung until 10 years ago. How is the old place? Brgds, Quadrico

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17th September 2007, 12:41 PM	#3
ay diyAudio Member Join Date: Sep 2007	Hi Ashok, Yes, the oscillator voltage stabilisation lamp ( La1) come on ok. I do have all the services manuals that are available on the internet already. I need to find out why I am getting the saw tooth type of waveform instead of sine wave. I get the same waveform even when I put the orginal Op Amp (the one still working) back into the circuit. I have run out of idea! Best regards, Alfred

17th September 2007, 01:00 PM	#4
Netlist diyAudio Moderator Join Date: Jan 2003	C2/C4 broken? /Hugo

17th September 2007, 03:01 PM	#5
ay diyAudio Member Join Date: Sep 2007	Hi Hugo, I have replaced C2/C4 with two new ones (1000uf 63V) and I am getting good voltage reading from both multimeter and osciliscope! For troubleshooting sake, I focus on the 33rpm portion and I have replaced C12 and C14 with two new 0.1uf already! Alfred

17th September 2007, 03:31 PM	#6
Netlist diyAudio Moderator Join Date: Jan 2003	I whish I could be of more help. In case like this I try to start from scratch. Confirm every transistor is good and in its proper position, check if the opamps are not reversed in the sockets, everything soldered well, trace the different voltages, measure every resistor, suspect the motor. I'm pretty sure it's something stupid, constantly overlooked. Your main question, why the sine wave is a saw-tooth, I can not answer. I have a TD125 in front of me and I’m willing to measure some voltages but the circuit is not the same as the MKII Keep us posted. /Hugo

17th September 2007, 03:49 PM	#7
ay diyAudio Member Join Date: Sep 2007	Many thanks for your help! I will go back to the basic and check everything again.... Alfred

12th January 2008, 04:12 AM	#9
ay diyAudio Member Join Date: Sep 2007	Hi quadrico, So you have a TD125 MKII as well! By the way, I have changed all the caps on the board but I still can get it to work! I do get a sinewave if keep the magnification low. Once turn up the magnification, it sinwave becomes a saw tooth! Let me know if you need any help to source the op-amp!

12th January 2008, 04:27 AM	#10
ay diyAudio Member Join Date: Sep 2007	Hi Quadrico, For the transistors, I am able to get C33725 & C32740 as the replacement. The op-amp I can get LM709CN (14-PIN) and MC1709CP1 (8-PIN).

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