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Electronics => Repair => Topic started by: vk6wa on February 03, 2017, 08:56:23 am

Title: HP1742A HV POwer Supply Fault
Post by: vk6wa on February 03, 2017, 08:56:23 am

Hi,

I have a HP1742A with an HV supply problem. The LV supply seems to be delivering the correct voltages according to the service manual. F1 in the HV supply is blown. Also the HF OSC transistor Q1 is suspect. The fuse I found fitted was a 1.5A slow blow and not a 1.0A as per the schematic. The switching transistor Q1 was marked as a MJE2801 but I can't be certain as it is nearly illegible. It appears to be a TO3P case outline. Any ideas would be most appreciated?

Kind regards,
Leigh Harrison
Schematic attached.

Title: Re: HP1742A HV POwer Supply Fault
Post by: james_s on February 06, 2017, 07:13:02 am

I would start by testing that transistor, does it test shorted?