Hi Guys
I’d appreciate some help choosing a new function generator. I have been using an old wavetek 191 which had some really good functionality (but has died). I 'd really like to have a new modern one that has the same functionality; particularly square wave, pulse and ability to gate and adjusts both pulse delay and pulse width and frequency. I have included a pic of the 191 as a reference. Very much appreciate your assistance with recommendations. Cheers
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Hi Ben
Whew, what a question. There are a multitude of different instruments out there having all sorts of functionality. I notice some go as low as 1µHz. That is 1 complete cycle every 1million seconds. Cant really see a use for that in the home workshop.
In reality it depends on exactly what you want / need / can afford ($$$). Amazon have pages of them, all different flavours. Emona instruments have a pretty good range and have a filtering system where you decide on the features to save trawling through all available.Some have frequency counters which could be useful.
That Wavetek used to be a pretty good instrument. If it were mine I would have a go at repair as you are probably going to pay $$$ for a pretty LCD screen and a few soft keys. Could be a possible option if you can get a circuit for it. It could even be a bit silly like a blown fuse. Anyway the power supply is where I would start.
Cheers Bob
PS. There is a download of the complete user/service manual here Service and User Manual - Wavetek 191 - Generator
This includes very comprehensive flow chart diagram trouble shooting guides for different problems. had a quick look and it seems to be a pretty complex instrument.
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nothing wrong with it have it serviced at a place like macservce…its a real good unit…
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just hook it to a freq counter if you have a cro as well you can look at the waveform…
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Thanks Rob et al. I appreciate the advice. I did have a go at fixing it, working through the manual as best I can… but to no avail. In truth I bought the unit from the US and it was set up for a 110v Ac supply. I changed the board over in the back, bought the correct rated and style fuse for it (3/8). Unfortunately, I stuffed up some how and put the old high rated fuse (3/4) back in it. My eyes aren’t what they use to be…apparently. I can’'t diagnose whats the problem is, but i suspect I got a power spike from the mains and this fried something. To say I was annoyed with my mistake was an understatement. All that to say I’d appreciate nay advice on how to fix it (if indeed this is a probable cause). I checked the main caps in the power supply side of things (while on the board) and they all seem to be OK. the bridge rectifiers seem to be working (as best i can tell). Some of the voltages across the PNP, NPN chips are out of speck and the manual only goes so far as how to diagnose (assumed knowledge level i don’t have). Symptoms are there is no main frequency control, only pulse and square out at frequency ranges up to 10Hz, thing above. Appreciate any advice on a potential fix.
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G’Day Bryan…can you provide more info on ‘macservce’ cheers. Much appreciated. i’d love to have it fixed if possible.
Hi Ben.
You apparently found the manual I referred to.
Yes the flow charts do assume a level of expertise and you have to appreciate they must do this. This is a service guide and the author would rightly assume it is used by a person with adequate qualifications.
This would turn out to be a mammoth task to fix remotely if the problem turns out to be beyond the power supply. Making sure this is all OK is the first step and probably as far as you could go. Don’t discount this task as without all the power supplies being in order you are only wasting time going further.
Power supplies. There is nothing super strange here. There are 3 split (plus and minus) supplies. +/- 15V, +/- 5V, both regulated and a +/- 31V not regulated. These supplies have to be correct or if not fix it before you could go further. As said if you need to go further it will be a mammoth task I think and maybe beyond your expertise which is unknown at this point.
I find the easiest place to measure PSU voltages are across the electrolytics. You will have to identify them, C2 & C6 +/- 15V, C11 & C12 +/- 5V and C13 & C14 +/- 31V.
If anything is amiss here you will have to backtrack to pre regulators. C3/C4, C7/C9. +/- 31V supply is not regulated. Expected voltages are marked on the circuit.
I notice there is a potentiometer R3, +/- 15V balance. At this stage under no circumstances touch this as you may unintentionally mask a fault. Also RV1 associated with the front panel and ground. Don’t touch this either, I have not searched to find out what this does or how to set it so leave it well alone.
This is your first line of attack. If you feel it is too much for you and indeed the test facilities at your disposal then I would advise go no further. I haven’t looked in detail but this looks to be a pretty complex instrument. If it needs to go to a repair facility which could be expensive you will have to weigh up the economics between repair or replace. Has to be up to you.
Cheers Bob
PS. Be careful of USA mains wiring. Not only 115 (120) Volts but black active and white neutral. Confusing to us mere mortals what???
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glenhunty or Clayton Victoria maybe spring-valve but south eastern suburbs of Melbourne they service electronic equipment but are expensive but do a good job they have a website just browse for them…i don’t know where u r…so …sice your in the states look for some service center that does electronic servicing…
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actually any ameuter radio dealer should point you in the right direction
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Hi Brian
Might probably need a professional who deals with test equipment Cal and Repair.
Cheers Bob
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well try radioshack if your in usa
1
- =T
f
1
- = F
T
if you have a cro and a counter find a service manual on the web
one over frequency equals time
one over time equals frequency
F=unit Hz
Tunit seconds
a doubbler or trippler for ac or rf will give you greater output coverage browse the web u may have to build one
If you care to read the thread a bit more carefully you would find that Ben purchased the unit from USA and had to change the power wiring to suit our voltage so forget bout Radio Shack.
And he has already found the service manual
Cheers Bob
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i saw later the bottom of the thread i just assumed he was down under…any brought 240 to110-120 would have done the job i have seen them
Read it again. He is “down under”.
It is the Function Generator that comes from USA. And it is designed to be dual voltage by changing wiring links.
Cheers Bob
PS. I am not getting into that discussion so I will drop it.
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me either really but obs he knows nothing about servicing the unit or basic knowledge of power supply construction…long day
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Thanks Rob
I’ll have another go at checking those voltages at the caps.Agree…I may just be up for a new unit. Even if I manage to ID a fried chip somewhere it maybe difficult to replace. But yes I’ll go back and check the caps and rectifiers…Thanks guys
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Hi Ben
Yes that will disclose any PSU problems. Note This is not testing the caps, just providing a pointer as what could be wrong. If you post the voltages measured across each of the caps listed we may be able to diagnose further. That is assuming you find a discrepancy. Stay away from the rear panel which carries all the 240VAC mains wiring. Be ultra careful here.
Cheers Bob
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G’Day Robert
C2 = 14.75V
C6 = 14.71V
C11= 0.2
C12 = 5.00V
C13 = 33.6V
C14 = 33.3V
C11 is a bit hard to measure (as it under another board) but I’m pretty sure I got it right. Voltage is low. I tried to measure the capacitance (while in situ) and it measure ‘Low’. This cap definatly looks suspect.
where to from here ? change out that cap? or back track to the pre-regularots C3/C4, C7/C9?
voltages as best I can tell from the circuit should be 21.5V and 11.3V for C3 & C4 and C7 & C9 respectively.
Update:
C3 = 22.4V
C4 21.9V
C9 = 10.3 V
C7 - couldn’t measure as inaccessible
Very much appreciate the help
Cheers
Ben
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Hi Ben.
C2 and C8 are a bit low but I don’t think that is any consequence, they should be 15V but don’t worry about that for now.
C13 and C14 should be 31V but are not regulated so 33V is OK.
C12 is 5V OK.
C11 is 0.2V definitely NOT OK. This +5V feeds just about everything and definitely would stop operation. It is a pity you have no access to C7 as this is the pre regulator side of the +5V supply and we need to know what that is. You will have to identify VR3. It is the right hand one of a group of 3 in the top left corner of the board. Look up the data sheet for LM7805 regulator (they are very common) and identify the pins. We need to know the voltage between common or ground and “IN” and “OUT”. The “OUT” should be the same as across C11 and the “IN” the same as across C7.
The volts across C9 is a little low which makes me think there may be a short on the +5V line pulling it down and the extra loading is affecting the -ve side a bit. There are several things that could be wrong here but may have a better idea when you measure those voltages. When you have done that power off and measure resistance across C11 or if that too difficult the resistance between VR3 OUT and Common, negative meter lead to common. This is the same as across C11.
C11 capacitance should be measured out of circuit. There are far too many things hanging off it for any in circuit measurement to mean anything.
Cheers Bob
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