any idea regarding lmc 567 testing
« on: March 22, 2020, 07:49:46 PM »
 Hi everyone.
Some years ago I had built this simple ring modulator pedal based around an LMC 567 and a TL 071 https://www.instructables.com/id/Ring-Modulator-Pedal/
Unfortunatelly I tried it the other day and it was dead. I carried a test around the ICs (the rest of the parts seem fine) using my signal generator (sine wave signal ) and oscilloscope and I realised that the signal is nearly lost (very low voltage square one) on pin 2 of LMC 567 (unfortunatelly I haven't got a spare one to test). Is this normal? How can I tell if the IC is good? What about the TL 071 (what should I check? iN and out similar voltage?)?
Thanks in advance for any info or advice

Ps. Is there any really good tested Ring Modulator lay out or schematic that you propose?


pucho812

Re: any idea regarding lmc 567 testing
« Reply #1 on: March 22, 2020, 09:26:10 PM »
post your schematic so we can help you
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

Re: any idea regarding lmc 567 testing
« Reply #2 on: March 22, 2020, 09:42:15 PM »
Hi Pucho812. If you check the link I've provided it includes a schematic  I've followed (along some more details of the project).   I  attach a jpg. just in case.Thank you.

pucho812

Re: any idea regarding lmc 567 testing
« Reply #3 on: March 23, 2020, 01:30:05 AM »
Sorry I missed that.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

moamps

Re: any idea regarding lmc 567 testing
« Reply #4 on: March 23, 2020, 03:43:24 AM »
Has this modulator worked before? R1 shouldn't be 100k, IMO.
567 is a PLL, which means that it change the state at output ( pin 8 ) when the input signal has the same frequency as  is the frequency of the local oscillator. The local oscillator is controlled with Ct-Rt values.
So,  replace the R1 with 100 ohms-1kohms resistor, then check the signal at pin 2, confirm that you can change it's frequency with the pot, apply the signal to the input (about 1V) and observe the state of the output  when these frequencies are equal. To see this change, temporary connect a resistor of any values higher than 10k between pin 8 and power input, + pole of 9V.

You can test it also by observing the frequency of the local oscillator ( pin 2 ) which should change somewhat when the frequency of the input signal is close.  If you have a dual trace oscilloscope it can be done easily.

Checking  TL071 is the next step. 

Re: any idea regarding lmc 567 testing
« Reply #5 on: March 23, 2020, 02:16:56 PM »
Has this modulator worked before? R1 shouldn't be 100k, IMO.
567 is a PLL, which means that it change the state at output ( pin 8 ) when the input signal has the same frequency as  is the frequency of the local oscillator. The local oscillator is controlled with Ct-Rt values.
So,  replace the R1 with 100 ohms-1kohms resistor, then check the signal at pin 2, confirm that you can change it's frequency with the pot, apply the signal to the input (about 1V) and observe the state of the output  when these frequencies are equal. To see this change, temporary connect a resistor of any values higher than 10k between pin 8 and power input, + pole of 9V.

You can test it also by observing the frequency of the local oscillator ( pin 2 ) which should change somewhat when the frequency of the input signal is close.  If you have a dual trace oscilloscope it can be done easily.

Checking  TL071 is the next step.


Thanks for the thorough reply moamps. To start with yes the modulator was working ok for more than 18 months (RARELY USED). 
I feed the input with 1v 4.5k sine wave signal.
I tried with a 180ohm resistor on R1 and a 15k resistor between pin 8 and 9v+ but there was no actual signal on pin 2 and pin 8. Then i replaced R1 with the old 100k one and everything went back to what it was before - slightly more obvious square signal on pin 2 (10 times less - around 0.1V - than the original 1V on pin 3).  The signal on pin 8 was a 3 times louder square one (about 3.5 V).
The pot didn't affect both signals. After a while the signal went off on pin8.  I have to admit that I tested the IC without isolating its part of the circuit from the op amp.  Can I assume that my IC is faulty, should I isolate it or should I proceed to an op amp test -what would that be? Thanks again.
« Last Edit: March 23, 2020, 02:41:14 PM by tedsorvino »

moamps

Re: any idea regarding lmc 567 testing
« Reply #6 on: March 24, 2020, 01:35:40 PM »
In normal operating conditions R1 cannot be 100k, you can test the IC as I explained, check the local oscillator at pins 5 and 6, you should be able to change his frequency with a pot connected to R12a and b. If you set both frequency, of input signal and of local oscillator to be equal, the state on the pin 8 should be changed. That's the test of this IC. Observe also what's happen at pin 2.

TL072 is a selective amplifier. At its output (pin6), you should measure about 4, 5V DC, modulated with amplified AC signal from the input. You should remove clamp diodes at its output for testing purposes.

Generally, this schematic looks messy to me but I'm not an expert of guitar pedals at all.

Re: any idea regarding lmc 567 testing
« Reply #7 on: March 24, 2020, 03:08:32 PM »
My op amp was a TL071 - the single version of TLO72. Checked it and replaced it with a good TL072 I had spare. i changed the pin connections according to the TL072 pin outs for a single opamp (just one side plus V+) and things went better. At least there were changes on the op amp side of things but still with a low output signal coming out of pin 2 of the LMC567.  I will carry on testing the IC on its own to see what's goin on. I may managed to burn both ICs in a way.....So I may have to replace LMC as well.
Thank you very much for the advice.


 

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