Frequency counter won't count.

• Frequency counter won't count.
  Posted by neo on 06 Jul, 2017 02:32
• I bought a HP 5340A and when i first got it counted and accurately. Then i put it on the shelf, not one thing changed and all it will show are zeros, and when i change ranges either MHz or GHz and the decimal point also changes. Could someone please help me before i rip my hair out?
• #1 Reply
  Posted by Ampera on 06 Jul, 2017 02:54
• Bolt an HP calculator to it. It will start counting perfectly
  
  The calculator, not the machine.
• #2 Reply
  Posted by neo on 06 Jul, 2017 03:06
• Quote from: TwoOfFive on 06 Jul, 2017 02:54

  Bolt an HP calculator to it. It will start counting perfectly
  
  The calculator, not the machine.
  

  
  Good laugh but ultimately not a solution to the existing problem of the expensive paper weight that used to count frequency then stopped.
• #3 Reply
  Posted by Ampera on 06 Jul, 2017 03:20
• You say it's expensive? Attempt percussive maintenance, that always helps matters.
  
  Sorry for joking around, I wouldn't know what the issue would be.
• #4 Reply
  Posted by neo on 06 Jul, 2017 03:31
• Quote from: TwoOfFive on 06 Jul, 2017 03:20

  You say it's expensive? Attempt percussive maintenance, that always helps matters.
  
  Sorry for joking around, I wouldn't know what the issue would be.
  

  
  The jokes are fine, they make me laugh and consequently help keep me from doing "advanced percussive maintenance" to the thing
• #5 Reply
  Posted by Vgkid on 06 Jul, 2017 05:40
• Here's the manual:
  https://elektrotanya.com/hp_5340a.pdf/download.html
   Since it previously worked, make sure everything is seated. Grab a dmm, and check the power rails. If it is like other HP counters that use a socketed relay for power, a bad connection will cause some strange results.
• #6 Reply
  Posted by TheSteve on 06 Jul, 2017 06:14
• Which input are you using, what is the input selector set to and what voltage/frequency signal are you feeding into it?
• #7 Reply
  Posted by neo on 06 Jul, 2017 06:35
• Quote from: TheSteve on 06 Jul, 2017 06:14

  Which input are you using, what is the input selector set to and what voltage/frequency signal are you feeding into it?
  

  
  50 ohm bnc i tried front and back. Voltage should be very low level, a hair above min level on my GFG-8020H. Frequency between 10 Hz and 55 MHz. It is through a scope probe but the same probe worked before i moved it.
• #8 Reply
  Posted by TheSteve on 06 Jul, 2017 06:55
• Is it a 10:1 probe? Anyway, you'll need to use the front BNC input for lower frequency use. Keep the range switch fully left.
• #9 Reply
  Posted by neo on 06 Jul, 2017 07:33
• 10x/1x probe and yes i did have it on 1x and i tried every range.
• #10 Reply
  Posted by neo on 06 Jul, 2017 07:37
• No matter what i do it locks at 00.000000 MHZ on 1 hz range, it used to go into a KHz range and measure
• #11 Reply
  Posted by Gyro on 06 Jul, 2017 11:51
• I'd check that its crystal oscillator is still working, especially if it's an ovened one. It might have suffered a thermal cycling related failure.
• #12 Reply
  Posted by neo on 06 Jul, 2017 12:43
• Quote from: Gyro on 06 Jul, 2017 11:51

  I'd check that its crystal oscillator is still working, especially if it's an ovened one. It might have suffered a thermal cycling related failure.
  

  
  When i tested it it read 7-8 MHz and climbing on my working frequency counter,  i writ it off to the scope probe but could that be it?
• #13 Reply
  Posted by rdl on 06 Jul, 2017 12:53
• Be sure to try with a different connector. Even 2 conductors of straight wire will be okay for testing. I bought a new oscilloscope once that came with 1 probe open, so never trust anything.
• #14 Reply
  Posted by neo on 06 Jul, 2017 19:56
• Quote from: rdl on 06 Jul, 2017 12:53

  Be sure to try with a different connector. Even 2 conductors of straight wire will be okay for testing. I bought a new oscilloscope once that came with 1 probe open, so never trust anything.
  

  
  I know both probes work as i have tested both. With either probe the frequency jumps between 7.5 and 8.5 MHz before semi stabilizing at 8 MHz and some change. I'm going to assume that is bad? It also only outputs when the unit is turned on.
• #15 Reply
  Posted by Vgkid on 06 Jul, 2017 23:56
• That doesn't sound good at all. 7-8MHZ, even measured with a scope. Is very very far from the correct frequency.
• #16 Reply
  Posted by alm on 07 Jul, 2017 00:08
• It could be that the capacitance of the scope probe messes up the oscillation. Especially if set to 1x. Set it to 10x and try to find a buffered node to measure the frequency at (for example an external 10 MHz output).
• #17 Reply
  Posted by neo on 07 Jul, 2017 00:22
• Quote from: alm on 07 Jul, 2017 00:08

  It could be that the capacitance of the scope probe messes up the oscillation. Especially if set to 1x. Set it to 10x and try to find a buffered node to measure the frequency at (for example an external 10 MHz output).
  

  
  Actually that is what i last tried, the 10 MHz out with 10x on the probe.
• #18 Reply
  Posted by alm on 07 Jul, 2017 00:34
• I must have missed that when reading your posts. If the 10 MHz output is outputting ~8 MHz, then there is definitely something wrong around the oscillator. The obvious place to start is measuring power supply voltages and ripple. The service manual should be helpful for this.
• #19 Reply
  Posted by neo on 07 Jul, 2017 05:31
• -15V      could not find board.
  +15V    OK
  -5V RF  OK
  -5V DG OK
  +5V RF OK
  +5V DG FAIL 4.67 MAXIMUM
  +11 TB OK
  While probing that last one it started counting again, i left it in self check and was watching for anomalies, so this give you any clues? I'm thinking maybe a loose card? It also started doing the 10 MHz out it should have been doing.
• #20 Reply
  Posted by neo on 07 Jul, 2017 05:42
•  
  I put the cover on and it broke again. By broke i mean not displaying and/or counting properly.
• #21 Reply
  Posted by neo on 07 Jul, 2017 05:57
• Also when it does work properly all i get is 3 digits.
• #22 Reply
  Posted by Vgkid on 07 Jul, 2017 06:11
• Check to make sure everything is seated, then recheck your power supply. Do you have the 175v rail?
• #23 Reply
  Posted by neo on 07 Jul, 2017 06:17
• Quote from: Vgkid on 07 Jul, 2017 06:11

  Check to make sure everything is seated, then recheck your power supply. Do you have the 175v rail?
  

  
  I took out and put all power cards back in and as for the 175V rail it has to work as the display is fully functional. Every digit lights except when counting where it will only display 3 digits.
• #24 Reply
  Posted by VK5RC on 07 Jul, 2017 08:37
• Does it have a freq standard input switch?  I had an old HP counter that the switch was intermittent, the internal reference goes through it as well.