Wavetek 182A Function Gen Teardown And Repair - Page 1
Forum section: electronics / repair

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 19, 2013, 08:03:27 pm
content: Hello everyone!This thread was asking about something I purchased but after it arrived it turned into a tear down and repair thread. The tear down and repair starts on post number 4.I havethe option to purchasepurchaseda Wavetek 182A function generator for cheap.I have wanted a function generator to learn more about making an inverter (like 12v to 120v) and also for transformer efficiency and even to learn how to figure out how many Hz a waveform is on an analog scope.I wanted to know if this model in specific can do that and also, would I be able to have this directly power a mosfet for quick and dirty temporary PWM control? Can this make a simple 60Hz sine or squarewave? I don't know myself because I am confused by the amount of different BNC connectors on the front of this and I can't quite figure this stuff out.Is there any other uses for a function generator?Thanks for all of your help!

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 20, 2013, 01:56:12 am
content: Nobody knows about this function generator?

author: w2aew
author_rank: Super Contributor
timestamp: August 20, 2013, 02:30:29 am
content: Can you generate signals of different frequencies and observe them on a scope? Yes, you can. The analog dial on thus generator won't allow to to set the output to a very precise frequency, but it will be close enough for most hobby applications.Will it be able to generate a simple 60Hz sine or square wave? Yes, it can.Can you use it to generate a PWM signal? Not directly. I don't see symmetry control, so it looks like the square wave is always 50% duty cycle. You can use a simple external comparator circuit and the triangle wave generator to adjust the duty cycle of the square wave.There are many uses for a function generator like this, too many to list.If you are confused on how to operate it, check out the instruction manual:http://bitsavers.informatik.uni-stuttgart.de/pdf/wavetek/182A_Mar86.pdf

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 20, 2013, 03:58:12 am
content: Quote from: w2aew on August 20, 2013, 02:30:29 amOkay then this sounds like it was a good buy for only $20 then!Hopefully I can figure out that comparator thing easily and mess around with some PWM when I get this.And yeah after thinking for a while I guess that even though the dial only goes up to 4 I can make 60Hz using .6 on the dial and the 100x multiplier.Thanks for your help.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 05:19:07 pm
content: Well I received the unit today and despite seeing the unit powered up (just plugged in and powered, not necessarily functioning) in the eBay listing, I decided that I'd have a look inside before turning it on.Looks pretty clean and pretty new inside at first glance, however I could see small black lines over parts of the chips and pcb.Then my eyes focused on the right front corner of the PCB marked "Output Amplifier" where the outputs on the front are attached. Some component, looking like a resistor or something similar is completely and utterly charred. Not only is that charred but an axial cap next to it has huge burn marks. I then figured I'd take a look at the top of the case that I had removed and set aside. In the corresponding corner of the top of the case there is a lot of soot and possibly a bit of melting indicating that that component went bang in a big way, which would also explain the small lines of black soot that had settled all over the pcb.I powered it on and checked all voltage rails, all seemed to be good. Checked a jumper that was supposed to be displaying a sawtooth wave, it checked good.I tried the 2V peak to peak output and got nothing at all on my oscilloscope.The resistor turned out to be a 54.9 ohm resistor that goes from the low output to ground. The closest I have is 100ohm so I connected it in and still got nothing on the output.I'll post pictures soon, until then, any help or suggestions are appreciated.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 05:54:20 pm
content: For some reason people manage to hook up an output to another output now and then, and I guess your unit has seen the same...But the schematics don't look too difficult, so start by looking if you still have the correct output on the output amplitude control and work from there. The final transistors in the output amplifier are most likely blown anyway.

author: Unknown
author_rank: Unknown
timestamp: August 22, 2013, 05:57:20 pm
content: Sounds like someone connected the low output to a voltage source with enough voltage to fry a low power 50 Ohm resistor. I'm guessing this instrument doesn't have fuses on the output? Did you check the wiring to the output connector? Depending how it was advertised, I would consider asking for a refund.Check the service manual for troubleshooting information. Do you have signal at step 3 but not at step 4 of table 6-3? Then you may be lucky and it's probably just the output amplifier. Looks like mostly jellybean parts in there. The good part is that failures will likely be fairly obvious: resistors that are open or grossly out of spec. Semiconductors that are open or shorted. The bad part is that the voltage could have easily taken out multiple parts. Q16/17 look like good candidates.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 06:00:31 pm
content: In the previous post I mentioned that a jumper labeled with a sort of sawtooth wave did show correctly but I decided to test it again and it actually shows nothing. What I saw before was noise from an improperly grounded probe.This means the generator part before the triggering and amplifier is not functioning.Anyone know where to start with troubleshooting that?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 06:06:21 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 06:00:31 pmStart at table 6.2/page 6-2 of the service manual, post again if something is not clear.http://www.ko4bb.com/Manuals/Wavetek/Wavetek_182A/182A_Mar86.pdf

author: willb
author_rank: Regular Contributor
timestamp: August 22, 2013, 06:09:42 pm
content: I own a 182A and id be happy to take it apart if you want to conform/verify any values that you doubt.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 06:18:32 pm
content: Quote from: PA0PBZ on August 22, 2013, 05:54:20 pmHow can I check the output on the output amplitude control? The final transistors appear to be 2n2219A and a 2n2905a. Both are physically intact and their heatsinks do get warm when the unit is powered up.Quote from: alm on August 22, 2013, 05:57:20 pmNo fuses on the output, the wiring to the outputs are intact. It was advertised as taken from a working environment and not tested. I'm not going to return it or ask for a refund.I tried step 1 and 2 of table 6-3. It fails to display a triangle wave (unless I'm wrong, to me it just looks like a large faded straight line with most of the timebases on the scope) on the emitter of Q11.I'll try 6-2 as it says to.EDIT: Step one of 6-2 tells me to check for -5VDC on pin 13 of U7 and +5VDC on pin 14 of U7, I read +1.2VDC and +1.8VDC respectively.It tells me to check Q4 and Q3 which are transistors and U2 which is an LM348N and check for "excessive loading". How do I go about checking those?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 06:40:38 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 06:18:32 pmLeft bottom of the picture I posted, but...QuoteI think you mean step 7, but anyway: check the power supply, Q3 and Q4 make the - 5 and +5 volts.QuoteIt tells you: "use board jumpers to isolate cause" I think it means that there are jumpers on the board to cut the +5/-5 traces to some of the circuit, to you pull the jumpers and if the power returns the fault is in the circuit you just isolated.Is the +15 and -15 correct?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 06:49:27 pm
content: Ok, maybe not pull the jumpers but cut the jumpers if they are just a piece of wire, see attachment.*disclaimer: I don't know if I found them all

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 06:54:53 pm
content: Quote from: PA0PBZ on August 22, 2013, 06:40:38 pmI'm not very good with electronics, that picture doesn't explain how to test it.Your right I do mean step 7.I don't think there is a problem with the power supply, all of the jumpers read their correct values, whether its +5 -5 +15 or -15, all of them are fine. Unless you think its really nessary to start desoldering jumpers.I'll follow pins 13 and 14 going to U7 and see where they go.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 07:22:49 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 06:54:53 pmAccording to the schematic these pins are directly connected to the +5 and -5 lines, so something does not add up here. Are you sure you are looking at the right pins?QuoteDo not desolder them, just cut them and solder them together again afterwards.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 07:32:21 pm
content: Quote from: PA0PBZ on August 22, 2013, 07:22:49 pmI failed bigtime. I've been sitting here tracing pins 8 and 9. I don't have much experience with IC's, that's why.Now that I have the correct pins, I see the correct voltages, those are fine.Sooo, that leaves U2 to be the problem?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 07:34:40 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 07:32:21 pmOk, continue the procedure in the manual.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 07:37:14 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 07:32:21 pmNo, if the voltages are correct U2 is fine.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 08:00:22 pm
content: Quote from: PA0PBZ on August 22, 2013, 07:34:40 pmOk I got all the way to step 11 of table 6-7. I don't understand what that means. Can you or someone else explain what it wants me to do?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 08:09:24 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 08:00:22 pm"Check for nonlinearity in the +- 1.25V triangle at the emitter of Q11 near the bottom of the x 1K through x 1M ranges"Set the range switch to 1K - 1M[near the bottom] Set the dial somewhere counterclockwise look at the waveform on the emittor of Q11, does it look like a triange?That is my understanding, without seeing the thing of course...

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 08:14:00 pm
content: Quote from: PA0PBZ on August 22, 2013, 08:09:24 pmLooks quite linear on all of those settings. Except if I have the ground of the probe not attached, then with no ground it looks triangular on some timebases.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 08:17:46 pm
content: How did you get to table 6-7? Was it a faillure in table 6-2 step 8? what failed?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 08:27:33 pm
content: Quote from: PA0PBZ on August 22, 2013, 08:17:46 pmI guess I accidently went to 6-7. IT passes step 8.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 08:37:14 pm
content: I'm working on step 12 of 6-2.It fails step 12. So it says to check U7 and Q7 and associated circuitry, help?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 08:58:53 pm
content: A little piece of advise before I go to sleep (it is 11P here): Check, double check and triple check what you are doing. Google everything, even when you think you are 99% sure... This function gen is not rocket science, the service manual looks ok, try to understand what is happening!

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 22, 2013, 09:02:38 pm
content: Quote from: EpicIntelGamer on August 22, 2013, 08:37:14 pmIt would make things easier if you post why it failed. What is the voltage at the emittor of Q11? What is the voltage at the cathode of CR10?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 22, 2013, 09:11:30 pm
content: Quote from: PA0PBZ on August 22, 2013, 09:02:38 pmIt failed because it shows .6V, which is not either higher than +1.25v or lower than -1.25v

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 23, 2013, 02:21:29 am
content: I spent another 3 hours on it and I tried replacing some components and I don't know what I did but where it used to show .6VDC off of Q11's emitter, now it shows 0VDC and nothing I do can make it come back (even after replacing the original components).EDIT: I have a feeling Q11 is bad, what are some common transistors I could replace it with?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 23, 2013, 09:33:05 am
content: Quote from: EpicIntelGamer on August 22, 2013, 09:11:30 pmThe way I read it is that either > +2.5V or < -2.5V is a fault condition, 0.6V seems ok.QuoteWhat voltages do you have on the base and collector? Is the +15 and -15 still ok?If you think you killed something start again with table 6.2 item 1.