UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Hameg HM307-3 Cleaning and Repair

OldTechFan96 · 25th May 2019, 2:30 pm

FET Installation:

I am sure that I have the FETs installed correctly. None of the junctions are touching.

Y position is set dead centre.

IC in:

Pin 1- 1.9V
Pin 14- 2V

IC out:

Pin 7- 2V
Pin 8- 4.9V

Now the EY voltages are unbalanced:

EY1- 8.1V
EY2- 21.9V

R198 is getting very hot and IC001 feels like it is getting warmer than it should.

Thoughts as to what is causing trouble:

FET has been installed incorrectly. Will try other permutations.
BF256 is not a suitable replacement for TIS69.
EY output balance potentiometer has been fiddled with in the past. I'll wait for further comment before I attempt adjusting this.

25th May 2019, 2:30 pm	#25
OldTechFan96 Octode Join Date: Jul 2017 Location: Newcastle Upon Tyne, Tyne & Wear, UK. Posts: 1,186	Re: Hameg HM307-3 Cleaning and Repair FET Installation: I am sure that I have the FETs installed correctly. None of the junctions are touching. Y position is set dead centre. IC in: Pin 1- 1.9V Pin 14- 2V IC out: Pin 7- 2V Pin 8- 4.9V Now the EY voltages are unbalanced: EY1- 8.1V EY2- 21.9V R198 is getting very hot and IC001 feels like it is getting warmer than it should. Thoughts as to what is causing trouble: FET has been installed incorrectly. Will try other permutations. BF256 is not a suitable replacement for TIS69. EY output balance potentiometer has been fiddled with in the past. I'll wait for further comment before I attempt adjusting this.