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

OldTechFan96 · 6th Jun 2019, 5:26 pm

The resistors are from a Vellemen resistor pack. The working voltage given is 250V. 188V was measured across R310. I agree that this is a bit close.

Z352 had -900V on each side. Checked C352 (1uf 25V tantalum) and its resistance varied between 10KΩ and 20KΩ. Replaced it with a ceramic capacitor and the voltage on the cathode of Z352 was closer to what it should be.

The voltages on T354 were higher than expected. Measured 140V rail and it was a bit high at 148V. The output of the rectifier was also high at 198V. I noticed that C305 was leaking electrolytic on the PCB. It was removed and the board cleaned up with IPA. R304 is good at 1200Ω. This is one of the hot resistors mentioned earlier in the thread.

I replaced it with a 47uf 450V radial capacitor I had around. I probably will replace it in the future with a 250V axial capacitor.

This only brought the 140V rail back to 146V, still a bit too high. I noticed in my notes that in the past the rail measured 133V. I wonder is something attached to the 140V rail is drawing less current? 140V goes to the astigmatism control and the Y final amp.

Attached are some diagrams with some more voltage measurements.

6th Jun 2019, 5:26 pm	#77
OldTechFan96 Octode Join Date: Jul 2017 Location: Newcastle Upon Tyne, Tyne & Wear, UK. Posts: 1,186	Re: Hameg HM307-3 Cleaning and Repair The resistors are from a Vellemen resistor pack. The working voltage given is 250V. 188V was measured across R310. I agree that this is a bit close. Z352 had -900V on each side. Checked C352 (1uf 25V tantalum) and its resistance varied between 10KΩ and 20KΩ. Replaced it with a ceramic capacitor and the voltage on the cathode of Z352 was closer to what it should be. The voltages on T354 were higher than expected. Measured 140V rail and it was a bit high at 148V. The output of the rectifier was also high at 198V. I noticed that C305 was leaking electrolytic on the PCB. It was removed and the board cleaned up with IPA. R304 is good at 1200Ω. This is one of the hot resistors mentioned earlier in the thread. I replaced it with a 47uf 450V radial capacitor I had around. I probably will replace it in the future with a 250V axial capacitor. This only brought the 140V rail back to 146V, still a bit too high. I noticed in my notes that in the past the rail measured 133V. I wonder is something attached to the 140V rail is drawing less current? 140V goes to the astigmatism control and the Y final amp. Attached are some diagrams with some more voltage measurements. Attached Thumbnails