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Robert Mani

Sun Oct 26 2008, 09:19PM

Registered Member #799 Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25

I am using the recording chip ISD1740 to make a recorder device and have run into a problem. The block diagram and circuit diagram are attached. At first I made the circuit on a bread board ( unsoldered) and it worked fine. I could record my voice for 23 seconds with a 53K oscillator resistor and played it back. However when I soldered all the components on a circuit board it initally worked for a few seconds and then it stopped working. Normally when the circuit is recording the LED is solid bright but now whenever I press the record button it flashes for a few seconds and then it dies.Pressing the play button does not play anything. The speaker also does not produce any noise and sounds dead. I thought I made a mistake in soldering so I took out all the components from teh circuit board and put it back on the breadboard and the same odd thing happens. The LED flashes for a few second by pressing the record button and dies. So far I have the same problem with two identical chips.
If you look at the block diagarm , is it possible that I have damaged the speaker amplifier or the AGC amplier? I have checked the connections several times and they are all correct and all the voltages (V digital, V analog and Vspeaker) are at the correct voltages and all the ground connections are correct as well. Anybody can suggest how I can troubleshoot this circuit or is it that the best way would be to buy another chip.

Thanks for your feedback.

Dragon64

Mon Oct 27 2008, 12:38AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

Im not sure but when you were soldering, you could have possibly damaged one of the IC's or transistors by the heat of the soldering iron.

Did you touch any of the IC pins longer then nessesary while soldering?

Robert Mani

Mon Oct 27 2008, 01:42AM

Registered Member #799 Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25

Yes it is posible that I have done that

Robert Mani

Mon Oct 27 2008, 02:04AM

Registered Member #799 Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25

sorry my previous reply was not complete. But I was trying to solder everything on a very small circuit board and soemtimes the molten solder jumps and makes a connection to where it should not. For this reason I had toremove the extra solder. I guess my biggest mistake was to have the chip on a case during the soldering whereas I could have easily soldered teh case first and after completion I could have put the chip in it. For teh next try I willdo it that way.

Dragon64

Mon Oct 27 2008, 02:15AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

Yes, that happen very frequently when soldering in tight places. Try using smaller 30 awg tin solder or a smaller soldering iron.

But for now, you should test the IC's and Transistors instead of buying an entire new set of them.

Robert Mani

Mon Oct 27 2008, 03:29PM

Registered Member #799 Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25

Thanks for your feedback HydraliskDragon. However i don't know what else to do to check if the IC's are working or not. I have checked all the connections and volagaes and they are all correct. For example the default value of the record pin should be VCC and when the push button is pressed it comes down to zero volts and it does exactly that. I even tried to connect the speaker at the output of AUD/AUX pin through a transistor as shown in the circuit digaram as an optional feature but no success. So I am clueless and I think it maybe worth while to buy another IC that costs only $8. If you have any other suggestion, will be glad to know.

Robert Mani

Mon Nov 03 2008, 02:50AM

Registered Member #799 Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25

Myestery solved!! Both recorder chips which I thought were damaged due to overheating when I was soldering them onto a circuit are working now. The problem was that the reset pin should be normaly floating and I had grounded it by mistake. The reset action powers down the chip momentarily. The design guide of the recorder chip warns that if recording is in progeress and power is brought down the chip memeory content gets corrupt and next time during recording the LED flashes 7 times as a warning sign. This was what I was observing. To remedy the problem one has to do a global erase action which means holding the erase pin for more than 3 seconds. I did that for both chips and now they are both working.

This is an experience to show that soldering does not so easily damage a chip unless the heating is excessive.

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