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New Function Gen: Gutted

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New Function Gen: Gutted

Post by CTV » Wed Sep 07, 2016 2:15 pm

I ordered myself a 2MHz DDS Dual channel function signal generator/counter. I was really looking forward to it and suspected nothing when the pristine box arrived. However upon opening the dozy packing twonks had been present. What person packs a 3-pin plug at the front of the device and worse than that, have the pins facing in towards the display. Logic would say pack the plug at the back of the box behind the unit.

So when removing the device from the box I could see the inevitable had happened, yep the LCD display is toast :aai I got straight on to the vendor who refunded my money and said keep the unit.

So I was wondering before I put it in the bin or salvage the case and parts would any whizz kid know if I can repair it, can the LCD be replaced with something similar?

Very gutted ole crusty...

fgen.jpg

 
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Re: New Function Gen: Gutted

Post by marc » Wed Sep 07, 2016 2:21 pm

Hi Chris,

Why oh why does this happen, it's not rocket science to pack a parcel is it ! :ccb

Just a silly thought, any chance of contacting the manufacturer and see if a display is available, it might just even be a sensible price.... maybe inno:

Marc.

 
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Re: New Function Gen: Gutted

Post by Mark Hennessy » Wed Sep 07, 2016 2:51 pm

It's almost certainly a standard unit - probably based on the HD44780 if it's a text-only unit.

https://en.wikipedia.org/wiki/Hitachi_H ... controller

Have you got a manual or other pictures that show the unit powered on - that'll give us some clues...

If this proves to be the case, replacements are cheap and plentiful.

 
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Re: New Function Gen: Gutted

Post by Mark Hennessy » Wed Sep 07, 2016 2:58 pm

Just looking around - is it this one?

http://www.ebay.com/itm/2MHz-Dual-Chann ... 1407197529

If so, it looks like a standard 16 character, 2 line display. Easy fix.

Take it apart and check where the connector falls. It'll be 16 pin (the interface is standard - 14 pins for the interface "proper" and 2 for the backlight). Then check eBay, etc, for replacements. You'll note quite a range of colour and size options - it'll be best to stick with what you have. E.g., blue might be tempting, but the backlight or contrast supplies might need tweeking.

Similar LCDs were discussed in this thread: http://www.vintage-radio.net/forum/show ... p?t=128109 - there might be useful background there.

So, hopefully a result :aad

 
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Re: New Function Gen: Gutted

Post by CTV » Wed Sep 07, 2016 2:59 pm

Manual is a PDF the model is a FY2200SP

fy2200sp.jpg

 
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Re: New Function Gen: Gutted

Post by Mark Hennessy » Wed Sep 07, 2016 3:04 pm


 
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Re: New Function Gen: Gutted

Post by sideband » Wed Sep 07, 2016 3:56 pm

Definitely worth trying to fit a new display....then you'll have a free function generator...brand new. I wonder how many others have been badly packed?

 
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Re: New Function Gen: Gutted

Post by CTV » Wed Sep 07, 2016 4:02 pm

All dismantled and I found and bought the exact 1602A replacement display module. If this works I got a new function gen for £2.99. Thanks to Marc H for advice and others for the encouragement, fingers crossed.

fg-1.jpg

fg-2.jpg

fg-3.jpg

fg-4.jpg

fg-6.jpg

fg-5.jpg

 
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Re: New Function Gen: Gutted

Post by FRANK.C » Wed Sep 07, 2016 6:07 pm

Well done Chris.
Unless there is something else damaged it will work.

Frank

 
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Re: New Function Gen: Gutted

Post by sideband » Wed Sep 07, 2016 6:40 pm

CrustyTV wrote:If this works I got a new function gen for £2.99.
:aad


Their loss, your gain Chris.

This is what sets us apart from the rest...we will have a go at fixing things and most times we'll be successful. It's how I got a lot of my test gear in the past including a brand new Philips audio generator that was dumped in the skip at Philips....'Not worth fixing' I was told. It had a s/c smoothing cap. One 2200uF 63V cap later, it was all up and running....that was 12 years ago. Apart from my digital meter, every other piece of test gear has been free with just minor repairs required.

 
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Re: New Function Gen: Gutted

Post by Cathovisor » Wed Sep 07, 2016 8:40 pm

As Mr. H. has pointed out, there are an astonishing number of 16x2 LCD displays out there but they all seem to use the same chip, or variation thereof.

I've just built an Ascel Electronic kit function generator, and after a false start where it (a) had a defective Atmega 168 and (b) I soldered two components in swapped :ccg it now works. But I've decided I'm not so keen on the black letters on yellow background LCD, so I ordered from Farnell a green letters on black background LCD, to give it that VFD look!

When it's all done, I'll post a piccy, although this highlighted some issues with it.


So I may still go buy me an HP/Agilent....

 
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Re: New Function Gen: Gutted

Post by CTV » Fri Sep 09, 2016 11:42 am

New LCD display arrived half an hour ago, installed and its working as can be seen below :bba

fixed.jpg

 
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Re: New Function Gen: Gutted

Post by Mark Hennessy » Fri Sep 09, 2016 12:17 pm

Result :aad

 
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Re: New Function Gen: Gutted

Post by marc » Fri Sep 09, 2016 12:19 pm

Nice one Chris !
from gutted to great all in a couple of days :bba

Marc.

 
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Re: New Function Gen: Gutted

Post by CTV » Fri Sep 09, 2016 3:29 pm

OK numpty boy question time.

As an interesting ( to me) test using the newly acquired/repaired function gen, I thought I would have a play with observing phase difference using XY mode on the scope.

I fed in a 1kHz 1V sine from CH1 on the fgen to CH1 on the TEK. Also a 1kHz 1V sine from CH2 on the fgen to CH 2 on the TEK. Now I seem to only be able to trigger CH1 and as far as I know that's correct. However how do you trigger CH2 as its just free running( un-triggered).

What I wanted to happen would be both 1kHz waveforms triggered. Switch to XY mode to see the diagonal trace,then adjust one signal to put it out of phase with the other. In XY mode as I increase the signal difference I would then start to see the Lissajous curve and the phase difference.

Because I cannot get both triggered the resultant trace is a spirograph

What am I doing wrong, sorry if its a newb question but you gotta start somewhere.

 
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Re: New Function Gen: Gutted

Post by Mark Hennessy » Fri Sep 09, 2016 5:27 pm

That's actually a really good question, and uncovers lots of interesting and subtle things...

First, it might be possible to correctly trigger on the two sine waves, but that depends on your 'scope. I'll get on to that in a second. But, before we do, we have a problem:

You have two sine waves, but not locked to each other. They also might not be exactly the same frequency. And you're trying to measure the phase difference. Unless they genuinely are the same frequency, the phase shift will be constantly changing. If you do contrive to display both on your 'scope, stably triggered, then you'll appear to have two sine waves that are in phase, but different (similar) frequencies. Clearly impossible!

Next, using X-Y mode to measure phase isn't the best way to do it. In fact, I rarely recommend X-Y mode at all. Yes, I know that every text book shows Lissajous curves, but apart from being very pretty and vaguely sci-fi, there is usually a better way to do it. I only use X-Y mode for setting up IFs. Oh, and at the risk of stating the obvious, the timebase is disabled in X-Y mode, so no triggering possible.

So, regarding the triggering, triggering on two separate signals isn't always possible - it depends on the topology of the scope. First, you have to be in Alt mode - where it draws channel 1 on one sweep, and then channel 2 on the other. The other option is "Chop", where the switch jumps between the two traces at 100kHz or more.

Having got Alt set up, you need to change the triggering to Alt (as opposed to Ch1 or Ch2). This means that the trigger signal is "sniffed" after the beam switch. Now, not all 'scope offer this option, and some that do aren't very good at working in this mode. On some Philips 'scopes, this mode is called "Comp" IIRC.

That clearly refers to analogue 'scopes. Whether your DSO offers the option depends entirely on luck. After all, there is no beam switching in a DSO, so no obvious place to pick up the trigger signal. As I said above, it's a really good question - when I get a chance, I'll look to see if it's possible on the Rigol...

For info, here is a better way to measure phase difference:

You know the variable timebase speed control? The one that has to be in the "Cal" position so that the numbers around the timebase switch (e.g., 1us/div) are accurate and correct. As soon as you adjust the VAR control, those numbers are no longer true. As a result, you've probably wondered why they provide the VAR option at all...

Here's where it's useful. Feed in the first sine wave, trigger from that channel only, and adjust the timebase speed so that one complete cycle occupies 8 divisions. You'll need to turn the switch clockwise until one complete cycle shows as more than 8, and then turn the VAR control anti-clockwise until you've hit 8.

Why 8 divisions? Because now, you've got 45 degrees per division. Voila :thumb

Then you enable the other sinewave, and by looking at where the zero-crossings are, relative to each other, you can measure the phase difference. Remember to turn VAR back to the cal position afterwards...

As mentioned above, your two sine waves are not phase-locked to each other; they are free-running. So, you'll see one sine wave is stationary, and the other will "run through" like a hum bar. Not much you can do about that. If you set up the scope to trigger alternately on each, as described above, then they will appear to be in phase, but at different frequencies - clearly impossible!

That definitely works on an analogue 'scope, and should also work on a DSO. There should be the option to fine-adjust the timebase speed, and happily, it should actually be calibrated (though not in the convenient 1-2-5 sequence).

Sorry for the long post, but it's one of those "simple question, complicated answer" questions. Hope it makes sense - for understanding purposes, it might help to dig out the analogue scope for a bit.

 
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Re: New Function Gen: Gutted

Post by CTV » Fri Sep 09, 2016 5:55 pm

Spent some time this afternoon playing and got it working. It was me not fully understanding what I was doing and not driving the f-gen correctly. I found a B&K company tutorial, it made things a little clearer. I output a 10kHZ 10V sine wave on CH1 & Ch2. I now had both triggered. I then adjusted the phase degree difference via the fgen not the frequency Dur! :ccg switched to XY and the Lissajous pattern could be seen. Adjusting the phase further showed the degree of phase variance.

lis0.jpg
Normal YT mode: FGEN CH1 and CH2 ouputting a 10kHz sine wave into CH1 & CH2 of scope and triggerd

lis3.jpg
XY mode: showing both sine waves in phase

lis1.jpg
XY mode: with phase offset on CH2 of FGEN, now scope displays out of phase Lissajous pattern

lis2.jpg
And further out of phase

lis4.jpg
XY mode: now showing a 90 degree phase difference

 
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Re: New Function Gen: Gutted

Post by Mark Hennessy » Fri Sep 09, 2016 7:04 pm

That's progress :thumb

Now you've worked out to make pretty patterns in X-Y mode. But this method won't enable you to measure the phase difference with any accuracy. So give the other method a go - the one where you adjust one complete cycle to 8 divisions (45 degrees per division). It'll be interesting to see if the numbers agree with what the function generator says (no reason to suspect it'll be anything other than accurate, but checking these things out is an important part of becoming familiar with the quirks of your gear, and it's good practice).

 
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Re: New Function Gen: Gutted

Post by sideband » Fri Sep 09, 2016 7:23 pm

My son used to be fascinated by the 'butterfly' (figure 8 on it's side) pattern I could generate when he was small. In his infant mind 'oscilloscope' became 'sillyscope', an expression that has stayed with me..... He used to tell his mum that 'daddy has been making patterns on his sillyscope'......

 
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Re: New Function Gen: Gutted

Post by Cathovisor » Fri Sep 09, 2016 7:33 pm

Anne used to refer to mine as "Silly" whenever it made an appearance in the front room. She was also amused by the notion of "Scilly Automatic" in the shipping forecast - homonyms can be devils like that...


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