Technical opnion about wave generator with problem

• Technical opnion about wave generator with problem
  Posted by israel on 08 Aug, 2013 23:03
• Hi guys.
  
  I have this wave generator with some problems, are all under control except the display indication ... is dead
  
  I have seen that there is voltage in pin 3 of IC that varies as a function of the position of the frequency control. i suspect that the reason that the display does not show anything could be the IC HEF-4379VP
  
  there a reliable way to know if the problem is that IC?
  I have found on the internet but is quite expensive. and before buying I would like to have some more expert opinion.
  
  attached images to see the team and the IC.
  
  
  sorry for my terrible english
  
  
  Best regards

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• #1 Reply
  Posted by AlfBaz on 08 Aug, 2013 23:29
• Have you checked for any output on the scan and data out pins?
• #2 Reply
  Posted by tinhead on 08 Aug, 2013 23:34
• the right trim pot didn't look good, check it first.
• #3 Reply
  Posted by fpliuzzi on 09 Aug, 2013 00:25
• Hello,
  The socket that the HEF-4379VP sits is in may be as tarnished as the right hand trim pot that tinhead pointed out. if you haven't done so already you may want to try lifting the chip up a bit on each side and then reseating the HEF-4379VP. The pins may be making poor contact. Worth a try anyway.
  
  Regards,
  Frank
  
  
• #4 Reply
  Posted by israel on 10 Aug, 2013 11:14
• Quote

  Hello,
  The socket that the HEF-4379VP sits is in may be as tarnished as the right hand trim pot that tinhead pointed out. if you haven't done so already you may want to try lifting the chip up a bit on each side and then reseating the HEF-4379VP. The pins may be making poor contact. Worth a try anyway.
  
  Regards,
  Frank

  
  
  was one of the first things I thought.
  
  
  
  
  I researched a little more, and I think that might be the IC makes the voltmeter function to control the display 
  
  I thought at the decoder, but this was fine.
  
  
  Anyone know where I could get cheap HEF4739VP?
  The only site I found sells it at $ 62 + shipping
  
  
  Regards,

  ---

  
• #5 Reply
  Posted by PA0PBZ on 10 Aug, 2013 11:48
• Are there any pulses on the scan lines (pins 10 - 13)?
  Is the thing oscillating (pin 25)?
  
• #6 Reply
  Posted by israel on 10 Aug, 2013 15:45
• Quote

  Are there any pulses on the scan lines (pins 10 - 13)?
  Is the thing oscillating (pin 25)?
  

  
  
  
  The tests show these results:
  
  1 --- 10.6820 v fixed
  2 --- GND
  3 --- The voltage varies according to the frequency and amplitude -4 mv to 1.8 volt
  4 --- 3.8993 v fixed
  5 --- no voltage
  6 --- 6.6758 v fixed
  7 --- no voltage
  8 --- 3.6862 v fixed
  9 --- no voltage
  10 -- 1.3440 v fixed
  11 -- 4.9380 v fixed
  12 -- 1.3462 v fixed
  13 -- 1.3460 fixed
  14 -- no voltage
  15 -- 5.114 v fixed
  16 -- 1.4945 v fixed
  17 -- 5.127 v fixed
  18 -- 3.3385 v fixed
  19 -- no voltage
  20 -- no voltage
  21 -- 4.9771 v fixed
  22 -- 4.9797 v fixed
  23 -- 3.5055 v fixed
  24 -- 4.9796 v fixed
  25 -- 3.2070 v fixed (no clock in scope)
  26 -- 3.3875 v fixed (not response at 250 khz)
  27 -- 4.9796 v fixed
  28 -- 4.9820 v fixed
  
  
  
  
  I see that pin 25 delivers no signal, according to the manual the clock signal is 250 KHz. I tried to inject a 250 KHz signal on pin number 26 (clock input) to see what happened, but there is no result.
  
  
• #7 Reply
  Posted by PA0PBZ on 10 Aug, 2013 15:58
• Well, if the thing is not oscillating and there is a supply voltage, it might be dead, I don't see anything like an enable line...
  All you can do is check the L, R and C on the clock pins, but if these are OK I think it's game over for the IC.
  I did a quick search and all I found is the one you found too for $62.