Help selecting Function Generator

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Hi Robert
figured go for the low hanging fruit first.
Re VR3. I got it. Ground was the middle pin, IN the left and OUT the right. 11.03V IN and 5.08V on the OUT.
Does this make sense or are we looking at the wrong VR or caps (sorry if I’ve got mixed up)?
Cheers

Update: C11 looking even more sus now?

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22

Hi Ben.
Sorry, but if you have got anything mixed up what you have measured is meaningless. This is quite long winded trying to trouble shoot by remote control.
On a brighter note what you have measured is what I would expect except for C11 and possibly C9 so maybe you are not mixed up.

NO. What you measured at VR3 out should be exactly what is across C11. They are connected.
To make sure lets have the polarity. With the negative lead on VR3 common the voltage out should be +5V. If it is negative 5V you have got VR4. When I said “top left corner” I am looking at the Generator board layout which I assume is the component side. I would think the board is probably marked too. Don’t know, you have it in front of you, not me.

If you do measure +5V at VR3 you will have to get access to C11 somehow to do a reliable measurement (an unreliable one is worse than none at all). If it is still 0.2V (or nothing) you possibly have a damaged board track or a bad or dry soldered joint. Another point to measure this is between VR3 common and connector Ji pin 5. If you look at the circuit you should see what I mean.
Cheers Bob

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Hey mate thanks for that. Much appreciated. Yet. I got a better reading (not easy) on that C11 and it 5.0V. I tied again to get a reading on the C7, no voltage at all. Put the conductivity test across it and got a beep. Figured that’s had it. Tried to pull it out (just so difficult- no room) by putting the iron on the terminals and wiggling it back and fourth a bit. The terminals just pulled outa the thing. So will never know if it was stuffed (most dissatisfying!). One of the teminals came out easy once i could get more heat on it properly but one of the terminal was directly mounted to the surface of the board and not in the hole. It was nearly impossible to get off …very odd. any way I’ll round up a 2200uF electrolytic and replace. Ben

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Hi Ben
What is your expertise in these matters. I am starting to have a few doubts. If you got the correct reading across C11 there better than a good chance C7 is OK and you have just destroyed the board for nothing.
The mind boggles when you found it desirable to replace that component when all the voltages ended up correct !!!

If you had it turned on or the cap still had some charge of course you would get a beep.
EDIT. Also you will get a beep as the capacitor is charging.

What is this “terminal”. Is it a small sleeve pulled out of the board or did the wire come out of the capacitor. I think you would have to work at it or be pretty ruthless to pull the wire out of the capacitor. If it is a sleeve out of the board it is a via connecting 2 or more layers and you have probably wrecked the board. Bye Bye function generator.

Anyway the power supply was the first line to check as without this being correct you are wasting time going further. This is a fairly complex instrument and without being very familiar with the works I don’t think it possible to diagnose remotely via a forum. You might get lucky. At best you would need a bench full of equipment and the knowledge to use it and if that is the case you would possibly have the knowledge maybe to fix it.
Cheers Bob

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Robert take it easy mate, ya nose is starting to stick up so high it might get hooked on something.
I got no voltage across the cap when live, couldn’t get a capacitance reading on it at all (when powered down after discharge) and when discharged it was showing it was conductive so i figured it mush have an internal short. Replacing a suspect cap is not destroying the board. I said ‘terminals’ ; you know the anode and cathodes that stick out of the end of the cap that you solder to the board. It’s not the PCB track. Look I really appreciate the help, it’s a tall order to fix something like this let alone remotely. Leave it there on the fix. Thanks again. Back to my original question…can anyone suggest an equivalent modern machine? Cheers Ben

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Hi Ben

I take offence at that. I am just trying to help here.I asked about your expertise so I have some idea who is on the other end. If you don’t need or want help just say so.

Re that cap you removed. I asked why. I assume it was C7 which you had difficulty accessing. That is why I had you measure the input and output of VR3. That is obvious on the circuit as the same point as measuring across C11 and C7. Hence the question re expertise. You obviously are unable to understand what a circuit (schematic) is able to tell you. The fact that the voltages are correct would indicate there is nothing basically wrong with either of these caps. I did say previously you can’t measure the value (µF) of a cap in this situation, there is too much hanging off it.

Short circuit caps. ALL caps will present a short at the application of voltage until they charge. Electrolytics can be particularly slow depending on value so it is possible your “beeper” will "beep’ for a short while at 2200µF until it approaches charge.

Replacement Function Generator. You should go back to my original reply. There are so many different flavours. You might like to browse to get some idea of what is available then you should first list all the features you want or need. Then you can do some filtering. As I said Emona Instruments have a range and the filtering system can cut down the search time. Some are not cheap. You can go from a basic DDS board with a few buttons and LCD display which will produce basic Sine Square Triangle signals right up to all singing and dancing units going for many k$$$.

Regarding my nose in the air. I am trying to loan you 50+ years experience here, dealing along the way with some pretty curly trouble shooting problems and I have never seen any success by going at a problem like a bull in a china shop (as the old saying goes). And I might add I have found that a fairly high percentage of problems originate at the power supply. This is why we start there.

Like I say, if you don’t want the help just say so. I am sure I can find other things to do.
Cheers Bob

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27

Hi Ben
Core have 3 Rigol generators and I think they must have another one as they recently compared the other one with a Rigol in a post. each have their pros and cons.
Cheers Bob

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