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Old 26th May 2019, 8:42 am   #30
WaveyDipole
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Join Date: Mar 2013
Location: Leicester, UK
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Default Re: Hameg HM307-3 Cleaning and Repair

Quote:
Originally Posted by WaveyDipole View Post
Pin 5 should be at -5v, and pin 10 at +6.8v. If not, then one of the corresponding zenner diodes (Z001 or Z002) might be at fault.
Quote:
Originally Posted by OldTechFan96 View Post
IC001 VCC voltages:

Pin 5- -6.2V. Too high.

Pin 10- +6.9V. Correct.

I've checked both zener diodes out of circuit and they are both good.
Looking at the sheet at right angles I misread the voltage at pin 5. Using a different reader that allows me to rotate the page at 90deg so I can read it the right way up, I see that the voltage at pin 5 should, in fact, be -6v, so your reading is not that far out.

Quote:
Originally Posted by OldTechFan96 View Post
X final amplifier measurements (the acceptable range is 84.1V-90.1V):

C of TR113- 112V
C of TR114- 96V

Both are unbalanced, like the Y amp.

R181 and R182 measure spot on out of circuit. The voltages on TR111 and TR112 are correct.
The "Troubleshooting the instrument" gives the range with position control centred as 95-105v and the circuit diagram shows a nominal 100v so these readings are not that far out. The voltage will shift depending on the position of the X-Pos control and as long as you can get them to balance out with the X-Pos control approximately centred, and the balanced voltage is within the range, then this should be OK.

Just curious, but is the AC input set to 220v or 237v?

It occurs to me that one way to test the functioning of the uA733 IC is to lift the outer end of R020 and R021 and feed a 0.5vDC supply into both ends simultaneously. The problem might still be down to what we are getting at the input.

Last edited by WaveyDipole; 26th May 2019 at 9:07 am.
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