Wavetek 130 Output issues

[technodruid]

First post!

Last night I finally got a chance to try out a wavetek 130 that I purchased a year ago or so after finally getting unpacked from a move. It was working really well, I was testing the various settings from the 50 ohm output into my rigol scope and it seemed to be fairly accurate. I was stepping through the course adjust from x10 to x100 and sweeping the dial looking for any distortions or drops/rises in amplitude. It all looked great.

Then when i switched to the 1M setting, the sine wave disappeared. I moved back to x100k and the sine wave was still gone. Something got messed up when I switched to the 1M setting.

Today I was trying to see if I could get any signal at all, and found that for settings x10 to x100k I can get "a signal" between 0.8 and 1.0 on the fine adjust dial, for sine, triangle, and square. However, each waveform has it's own issues.

Broad description of behaviours

• All have a DC offset where they did not before (-0.3V sine, -1.2V triangle, 5V square)
• No discernible output for any amplitude or any range on the 1M setting for any of the three waveforms
• Sine and triangle now output as a reversed shark fin and reversed sawtooth respectively
• Sine is the only waveform that matches the peak-to-peak voltage dial setting, at 10V half way. Triangle is about double the amplitude at 20V half way, square is about 200mV half way
• no visual indications of blown or damaged parts
• Power supply is absolutely fine
• DC offset dial works
• have not checked sync, nor would I know how at this point.

I have a google doc started where I have begun to log my measurements here.

I am hoping it's just an issue with the opamps? I only have a very poor quality manual scan on hand so troubleshooting from what I have is very slow and difficult.


Cheers.

[redwire]

Welcome to the forum

Somewhat common to blow a signal generator's output stage. See if Q39, Q40 are OK, any smoked resistors. If you short the output or connect to something inductive like a transformer, they can get blown.

If OK, then check the power supply rails, the +/-15V regulators at TP2,3 and +/-6V as well TP5, 6 which powers SYNC OUT. Is that signal OK?
It's getting old, so the electrolytic capacitors are likely dried out. There's only 8: Six Sprague 100uF 16V, and two 1,000uF 35V, I just replace them all it's less hassle.

Otherwise I think you'd need to go inside it with a scope. The main oscillator IC4/5 CA3030 should work at 1MHz scale but you can check at TP7 to see if that is the problem - or if (downstream) the sine/tri shapers or output amplifier crap out. It's a bit weird everything stopped working right.

These are useful gear because they have a strong output, to 40Vpp. Later models added protection diodes and a fuse to the output.

Manual & schematic http://www.bitsavers.org/test_equipm.../130_Aug72.pdf

[technodruid]

Thanks for the tips redwire!

Somewhat common to blow a signal generator's output stage. See if Q39, Q40 are OK, any smoked resistors. If you short the output or connect to something inductive like a transformer, they can get blown.

These appear to be ok. I do have some replacements on hand, I swapped them out and checked the forward voltages across their pins, everything looked nominal. Ran with the replacements, same issue. No smoked resisters that I can tell.

If OK, then check the power supply rails, the +/-15V regulators at TP2,3 and +/-6V as well TP5, 6 which powers SYNC OUT. Is that signal OK?
It's getting old, so the electrolytic capacitors are likely dried out. There's only 8: Six Sprague 100uF 16V, and two 1,000uF 35V, I just replace them all it's less hassle.

All caps were swapped out. They were all outside 20% out of circuit. ESR was a little high too. Signal is a little cleaner, but still "half" a signal.

+/-15V looks good. Tuned it in, as it was close to out of spec wrt details in the manual. No change to output.

+/-6V looks ok. Could be better. TP6 shows a slightly larger voltage difference at 6.3.

Sync out has NO squarewave. It only shows ~5V DC.

Otherwise I think you'd need to go inside it with a scope. The main oscillator IC4/5 CA3030 should work at 1MHz scale but you can check at TP7 to see if that is the problem - or if (downstream) the sine/tri shapers or output amplifier crap out. It's a bit weird everything stopped working right.

HOWEVER: While testing TP7 for voltage and then through my scope, the sync signal appeared. It was bang on with the dials. Also, TP7 appeared as a triangle wave with the same frequency. I didn't check the P-P voltages before the signal disappeared. I had swung the course selection around to 10, 100, and so on and swept the fine tune dial. The sync was working great. I switched over to 100k and the sync went dead. It did not recover after power off, or after disconnecting and reconnecting the test points as I had when it started running. After the sync pulse disappeared, the triangle at TP7 went back to the original faulted pattern I was seeing on the 50ohm output: Triangle on the falling edge, square on the rising edge. I take it the main square generator, or maybe some components associated with either the 100K or 1M setting (or both) may be at fault?

CA 3030's look good. Their output pins show what I see on the output. I also checked the diodes around the triangle wave section since the maintenance section of the manual mentioned them. They all had an expected voltage drop, nothing out of the ordinary.

[technodruid]

Perhaps there's an issue with the CA3036?

[redwire]

Take a plastic pen and gently tap things, the PC board etc. to find if that aggravates the signal coming and going. It sounds like you've got a loose connection? Maybe an oxidized IC socket or switch like SW1. I use DeOxit on them.
The master oscillator "integrator" I would get working consistently first at TP7. When it croaks stops osc., take voltage measurements on the CA3030 and CA3036. That will tell us what's going on.

[stj]

ah yes, old ic sockets.
i just spent yesterday replacing about 60 of them from about 1980
i also have a scope with bad (loose) transistor sockets - dont trust those either.
one other thing, if you mix god and tin or silver and tin, you get tarnish.

[redwire]

IC5 for the oscillator is CA3030 DIP-14(!) single op-amp, an older part. It would be replaced by the '741 but that is in a DIP-8.
Not sure what IC4 CA3036 transistor array is doing, it could be to lower the input bias current but a '741 already achieved that compared to the CA3030, or temperature compensation.
One cal trimpot could be looked at, R28 looks like an offset (not for frequency).