[Fixed] Troubleshooting display of function generator

[leppie]

FG is Escort EFG-2230. I cannot find any manuals for this or the newer (but seemingly equivalent) model, EFG-3230. Escort was bought by Agilent in the mid 2000's.

The 7 segment display is driven from an Intersil ICM7216D. Initially I thought it was the problem and ordered one from ebay for 6 dollah. It is still on the way, but I have found out that it is probably not at fault.

The FG however works perfectly, but displays nothing but zeros.

Both the output and the input is connected to pin 28 of the IC. There is a push button to select what is displayed. According to the datasheet, VH is 3.5V and VL is 1.0V.

I probed pin 28 in both modes and can see it is going via some signal conditioning circuit so that the incoming signal is between 0 and 5 volts.

For output, the oscilloscope shows a square wave (regardless of wave type) with a high peak of 5V and a low peak of 3.6V.



For input (tiny 300mv from scope calibrator), the oscilloscope shows a square wave with a peaks between 4 and 5 volts. The input sensitivity for the frequency counter from what I can gather is 30mV p-p.



The entire circuit is made from discrete bits and some CMOS IC's and the Intersil part.

It has 2 test points, TP1 shows a -0.5V and TP2 shows a triangle wave. I am not at the equipment now, but will update the exact details for these test points later today.

Given the lack of schematics, I don't really know where to go from here. I can tear it down and provide pictures also if it will help.

Thanks

Update:

I have added images to show what the oscilloscope says on the requested pins (name is pin number). Pin 27 is connected to ground. 0V is line 1 (zero-indexing for those VB'rs!) from the bottom, 1V/div. Sorry for poor quality in some of them

Update 2:

From the schematics of the Voltcraft FG1617, it appears the internals are very similar. You can find the schematics from the link below.
https://www.eevblog.com/forum/beginners/new-to-me-function-gen-tipshelp/msg142862/#msg142862

Based on the above, I am suspecting there is an issue with something not pulling -5V correctly. Perhaps TP2 is meant to show -5V instead of the -0.5V I see. 

[HalfSpace]

Hi leppie,

You may want to check with your oscilloscope pins 1 (control input), 12 (reset input), 14 (range input), 27 (hold input) and 26 (osc output) on the ICM7216D. All these pins should have clocking signals.

On the ICM7216D data sheet page 15 shows a typical circuit using this device which could be a good start point.

HalfSpace 

[nadona]

Racal-Dana 1992 use ICM7218B and it's manual is available from many websites.

[leppie]

Racal-Dana 1992 use ICM7218B and it's manual is available from many websites.

That looks way more complicated than what I have

[leppie]

Hi leppie,

You may want to check with your oscilloscope pins 1 (control input), 12 (reset input), 14 (range input), 27 (hold input) and 26 (osc output) on the ICM7216D. All these pins should have clocking signals.

On the ICM7216D data sheet page 15 shows a typical circuit using this device which could be a good start point.

HalfSpace 

Done and added to the first post.

[HalfSpace]

Hi Ieppie,

All the signals look good except pin 28 which is not toggling low (under 1v). Can you disconnect pin 28 from the rest of the circuit and feed into it a 0-5v 1 kHz signal? Maybe from the BNC output of the FG through a 2.2k resistor to protect the input pin. This should tell you if your IC is ok.

HalfSpace

[leppie]

All the signals look good except pin 28 which is not toggling low (under 1v). Can you disconnect pin 28 from the rest of the circuit and feed into it a 0-5v 1 kHz signal? Maybe from the BNC output of the FG through a 2.2k resistor to protect the input pin. This should tell you if your IC is ok.

I was thinking that too. Good idea using the FG output to create the signal

[leppie]

I tried with pin 28 disconnected and sending in 0-5V 1kHz squarewave and still not working.

I have noted a possible short in the 4066 IC though. Unless there is a trace underneath it I can't see, that might be a problem. Pin 14 is feeding this. Will have to unsolder it to see if that might be a dud.

I also have started making a list of all the IC's (mostly opamps). It seems like a simplified design of the Voltcraft.

[HalfSpace]

Hi leppie,

Maybe the ICM7216D is faulty.

Check pin 28 with your oscilloscope when feeding the 1 kHz signal in via the 2.2k resistor. Does the signal go from 5V down to zero?

Also check if the driving circuit disconnected from pin 28 is now toggling down near zero.

Halfspace 

[leppie]

Maybe the ICM7216D is faulty.

Check pin 28 with your oscilloscope when feeding the 1 kHz signal in via the 2.2k resistor. Does the signal go from 5V down to zero?

Also check if the driving circuit disconnected from pin 28 is now toggling down near zero.

Good thing I ordered one. When it will show up, who knows, our postal services are on strike

I will check and report back the findings as well as post the IC parts listing later tonight.

Thanks for your help

[leppie]

Maybe the ICM7216D is faulty.

Check pin 28 with your oscilloscope when feeding the 1 kHz signal in via the 2.2k resistor. Does the signal go from 5V down to zero?

Also check if the driving circuit disconnected from pin 28 is now toggling down near zero.

Driving circuit is fine. Nice clean 0-4V square wave for both input and output.

Pin 28 is 5V, which would indicate it is faulty (unless there is a magical low ohm pull up hidden, but no what I can see. Picture attached.).

Thanks for your help. Now to wait for the replacement IC.

Hopefully that will fix it \o/

[leppie]

Hi

The replacement IC has finally arrived.

Replaced the defective one and viola, it works again!   

No EEVblog repair curse here!

Thanks for all the help.

The defective chip seemed to have a short between VCC and pin 28.

Cheers

leppie

PS: Perhaps I should tackle the repair of my TDS 340 now