Author Topic: Wavetek 145 amplitude / distortion  (Read 4492 times)

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Offline njmike

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Wavetek 145 amplitude / distortion
« on: November 03, 2015, 02:17:54 am »
Hi, I'm new to the forum and just recently picked up a Wavetek 145 from eBay. The unit was reasonably priced so I took a chance and started to do some tests. This is my first function generator so forgive my rookie questions as I learn :)

The exciting part of doing the tests is I finally used my Tek 465b/dm44 scope after sitting in storage. I did tests on this scope as well as on a Rigol DS1054Z. I did search on the forum and it seems common that signals typically are distorted on all function generators towards their high end limit. In the 100k frequency setting, the signal looks like the first picture. I get similar results on the Rigol.

The other question I had was the amplitude on the sine function is a max of just over 100mv p-p. The manual says the unit is capable of 30v p-p (15v p-p in 50 ohm). Is there something wrong with the unit or user error somewhere?  :-//
 

Offline ez24

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Re: Wavetek 145 amplitude / distortion
« Reply #1 on: November 03, 2015, 02:43:18 am »
Hi, I'm new to the forum and just recently picked up a Wavetek 145 from eBay. The unit was reasonably priced so I took a chance and started to do some tests. This is my first function generator so forgive my rookie questions as I learn :)

The exciting part of doing the tests is I finally used my Tek 465b/dm44 scope after sitting in storage. I did tests on this scope as well as on a Rigol DS1054Z. I did search on the forum and it seems common that signals typically are distorted on all function generators towards their high end limit. In the 100k frequency setting, the signal looks like the first picture. I get similar results on the Rigol.

The other question I had was the amplitude on the sine function is a max of just over 100mv p-p. The manual says the unit is capable of 30v p-p (15v p-p in 50 ohm). Is there something wrong with the unit or user error somewhere?  :-//


What picture ?

Is your probe set at 1x and the scope at 1x  - if so that is why the Wavetek was on eBay -  I am sure sold as "unable to test"   :-DD  FYI  I have a Wavetek 145 and it outputs the 30 volts - mine was sold on eBay as "unable to test" but I was lucky.  (been unlucky more times than lucky).  Make sure your Attenuation is set at 0     These are well designed units so my first guess is operator error, so play with all the settings and see what happens. 




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Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #2 on: November 03, 2015, 03:03:34 am »
Doh, forgot the picture! It's attached. The signal of the scope and the corresponding settings on the wavetek.

The function out is going directly into the scope and it's terminated using a 50-Ohm feed through terminator. The tek and rigol channel inputs are 1M. The attenuation is set to zero and even when I turn both attenuation and vernier fully clockwise still nothing over ~ 100mV.

I'll take some more pictures tonight.
 

Offline ez24

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Re: Wavetek 145 amplitude / distortion
« Reply #3 on: November 03, 2015, 04:10:15 am »
Can you hook up your Wavetek directly to the Rigol with BNC to BNC (I do not have a 50 ohms connector) (this may go against the rules)
and show the hook up and the screen shot from the Rigol (so I can see the settings).  I do not have a Tek 465b (wished I did) and do not know what your vertical setting is and that is what we are talking about (not the horizontal that you gave)

I can duplicate your setup if you give enough details using the Rigol  DZ1054Z.  So close ups of the Wavetek and Rigol.

Once we determine your Wavetek is bad, someone on this forum may tell you how to fix it. 
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Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #4 on: November 03, 2015, 05:10:54 am »
Can you hook up your Wavetek directly to the Rigol with BNC to BNC (I do not have a 50 ohms connector) (this may go against the rules)
and show the hook up and the screen shot from the Rigol (so I can see the settings).  I do not have a Tek 465b (wished I did) and do not know what your vertical setting is and that is what we are talking about (not the horizontal that you gave)

I can duplicate your setup if you give enough details using the Rigol  DZ1054Z.  So close ups of the Wavetek and Rigol.

Once we determine your Wavetek is bad, someone on this forum may tell you how to fix it. 

I just came up from the shop and did a bunch of tests. I can do another test BNC-to-BNC tomorrow but here's some pictures.

The first two are of the wavetek and tek 465. I set the wavetek to 1khz (give or take) and you can see the 50mV/div. It's actually ~ 200mv P-P where I think I said it was just over 100 in my last post. Nevertheless, way lower than spec with no attenuation.

The third and fourth pics are 100khz test with the Rigol. I should have taken a Vpp measurement and toggled some of the stats! But you can see the distortion. I will repeat your test steps tomorrow, but yeah you need a 50-ohm termination to get correct voltage measurements. The one I'm using is http://www.amazon.com/Cal-Test-Electronics-Feed-Thru-Terminator/dp/B009QBL2T2 - good quality, but pricey (although not as expensive as the Tek terminators!!).

The tek 465b is a nice scope, very popular apparently. I bought it about 10 years ago for ~ $165. Came with probes, some extra parts and original manual. I'm still learning it but definitely recommend it. I think it's good to have both a DSO and CRO in the shop :)


« Last Edit: November 03, 2015, 05:12:42 am by njmike »
 

Offline FlyingHacker

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Re: Wavetek 145 amplitude / distortion
« Reply #5 on: November 03, 2015, 05:28:13 am »
Do all waveforms suffer from the same lack of amplitude?

Just for grins, what happens if you enable the attenuator?

Find a service manual and start poking around inside? I would start with some contact cleaner on the switches to rule out simple tuff first. Then move on to supply rail voltages and ripple per the service manual. Possibly go through the calibration procedure first, and see what is not up to snuff. I have had some old toys get fixed just by doing a calibration.
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Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #6 on: November 04, 2015, 03:14:59 am »
Yes I know all of the alternating signals suffer but I should check the DC signal also. But first...

I decided to take the covers off for a visual inspection and found the 470uF cap on the function out was blown out. There's a hole on the one side and some brown stuff was on the cap, guessing the dielectric. I will hunt down a replacement cap but I'm curious what effect a blown cap would have on function out? I know what caps are and their characteristics but I'm hunting down the cap on the schematic still.

Other than the above things look OK but the ceramic caps appear bloated and some have a seam showing. Guessing this is normal with age?

I have a feeling this will turn into a (fun?) project. I'm wondering if I should keep it for the $100 I paid with shipping or return it.



 

Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #7 on: November 04, 2015, 03:59:10 am »
Pics of the blown cap. Looks like a jerry rig?  :-DD

I think it's either C6 or C8.

 

Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #8 on: November 04, 2015, 04:22:02 am »
These are not C6 nor C8; those are on the regulator board. This cap and two resistors looks like a mod, but what for?

Can anyone with a 145 verify?

 

Online lowimpedance

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Re: Wavetek 145 amplitude / distortion
« Reply #9 on: November 04, 2015, 04:35:32 am »
Certainly some bodgy mod to AC couple the output. Use your CRO to check the waveform where the coax inner meets the 33 ohm resistor. If good get rid of that bodgy crap and connect the coax back to the BNC (get rid of it anyway!). If still a bad waveform then check the signal at the input to the power out stage (wiper of R185), if good here then the issue is in the power amp
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline dacman

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Re: Wavetek 145 amplitude / distortion
« Reply #10 on: November 04, 2015, 05:36:34 am »
All the output/input connectors should be connected directly to the PCB, some with removable connectors but the output was soldered.  Could you set the frequency vernier to CAL and the DC OFFSET to OFF?  The 2.7 kOhm, 33 Ohm, and electrolytic capacitor should not be there.
« Last Edit: November 04, 2015, 06:08:05 am by dacman »
 

Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #11 on: November 05, 2015, 11:54:30 pm »
I removed the blown cap and resistors and soldered the coax back to original state. No change in signal quality/amplitude. I'm going to request a refund. Thanks to everyone who helped.
 

Offline FlyingHacker

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Re: Wavetek 145 amplitude / distortion
« Reply #12 on: November 06, 2015, 01:15:51 am »
Perhaps list the seller here so none of us buy it the next time around...  :scared:
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Offline ez24

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Re: Wavetek 145 amplitude / distortion
« Reply #13 on: November 06, 2015, 01:48:48 am »
Perhaps list the seller here so none of us buy it the next time around...  :scared:

at least tell us what the conditions were   ie  "Unable to test"  but 30 day return

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Offline dacman

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Re: Wavetek 145 amplitude / distortion
« Reply #14 on: November 06, 2015, 02:18:15 am »
What does the signal look like around R209, R271, and R256?
 

Offline njmike

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Re: Wavetek 145 amplitude / distortion
« Reply #15 on: November 06, 2015, 03:09:56 am »
I'll let you guys know if I send it back but I'm discussing options of keeping it for a paperweight :-DD

dacman, I looked over your question the other day. The DC offset was making no difference on any signal. I did do a couple tests in the calibration section of the manual (see pic).

Step 1 voltage across C112 was good +15v, within tolerance.
Step 2 voltage across C111 was OK, -15v, slightly out of tolerance (about .1 vs. .005)
Step 3 voltage across TP1 and TP2 was negligible (in mV) - nowhere near +15v.

That's as far as I got last night thinking this unit is probably just toast adding it all up. What do you guys think, is the 145 worth fixing? It would be a good learning project that will definitely be challenging.
 


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