I have a Rat problem!

[foozertone]

     I built a rat from the Tonepad layout http://www.tonepad.com/getFile.asp?id=89. It worked when I built it. It worked when I boxed it up. Acouple weeks later, I went to use it and it don't work no 'mo. It's dead. Here are my readings:

Batt-9.82
1-9.16   8-9.85
2-4.90   7-9.78
3-4.39   6-4.91
4-0.00   5-0.00

Anyone have any ideas what to look for?

I appreciate any help

Jeffrey

[petemoore]

http://www.datasheetcatalog.com/datasheets_pdf/L/M/3/0/LM308.shtm
  Batt-9.82
  1rst thing to check  !
   
1-9.16   8-9.85  [either the battery dropped some voltage, or pin 8 reading is a typ-o, the opamp potential can't exceed the power supply].
  Not sure what 1 and 8 should be doing, they're the frequency compensation pins.
  2-4.90 is the -input and this is about 1/2 supply
  3-4.39 Same with 3, the +input looks ok.
  4-0.00 Gnd. = 0.00v
  5-0.00 N/C.
  6-4.91 The output looks good too, has some room for the voltage to swing.
  It looks on the scheamtic that pins 1 and 8 are not connected externally except for the cap between them, they are getting the pin voltage from internal connection I *think [which *would mean the voltages are ok], hard to tell except to me it doesn't look connected [lm308 schematic] to V+...someone else can chime in...
  7-9.78  IIRC there's a 100ohm resistor between power supply which probably accounts for the .04v drop from supply.
  Sorry I couldn't figure out and be more help on pins 1 and 8.
  If socketted, you can pull the opamp and look for shorts to 1 or 8 [doubtful], those pins would read open with the opamp removed because the compensation cap blocks DC.

[Minion]

As pete says ,I don"t know if you are supposed to have Voltage on Pins 1 and 8 as these are Compensation pins but the others look OK....

[petemoore]

  I would just try to find or wait for someone to chime in...or take opamp out, test those pins for any stray connections.
  And check for peripheral problem like something touching or some other offboard problem.
  Then maybe put a single opamp in there [no compensation but should amplify].

[JOHNO]

I just measured mine
batt voltage 8.6
1, 7.94
2, 4.3
3, 3.9
4+5, 0
6,4.3
7, 8.6
8, 4.37
Looks to me like pin 8 is at about half the supply voltage so you might want to start looking there.