Tek 7603 - a quick fix? - UK Vintage Radio Repair and Restoration Discussion Forum

Joe_Lorenz · 14th Nov 2025, 9:45 pm

Hello,

one of my sons shoved a 7603 on my bench. It had been sitting for years and upon firing it up (yes, I know ... no good idea) it gave in after half a minute of operation. A hissing noise and a vanishing beam. It seems to be an early one, #100044 according to the manual.

As I did not have much time to investigate thoroughly I just did a visual inspection: I could not spot any exploded tantalums or other destroyed capacitors without dismantling - and that does not seem to be such a straight forward job as on my 5-series scopes.

Are there any known typical faults, or do I have to proceed methodically? I tend to assume the big electrolytics of the psu might be dried out.

Kindest Regards, Joe

tony brady · 15th Nov 2025, 7:46 am

the tants on the +15V & -15V lines can go short in the mainframe & the plug in modules

basically check the all the regulated voltages first. if there is a short on the 15v rails pull the modules out to see if it clears

the mallory caps in the power supply often fail causing low voltages and hum effects on the screen. a 'hissing noise sounds more like the high voltage transformer has suffered from damp - this is in a screened box at the rear with the EHT lead coming from it. I had one where the potted multiplier failed but that didn't hiss, just no display was visible.

cheers
Tony

15th Nov 2025, 7:46 am	#2
tony brady Hexode Join Date: Mar 2014 Location: Peacehaven, East Sussex, UK. Posts: 289	Re: Tek 7603 - a quick fix? the tants on the +15V & -15V lines can go short in the mainframe & the plug in modules basically check the all the regulated voltages first. if there is a short on the 15v rails pull the modules out to see if it clears the mallory caps in the power supply often fail causing low voltages and hum effects on the screen. a 'hissing noise sounds more like the high voltage transformer has suffered from damp - this is in a screened box at the rear with the EHT lead coming from it. I had one where the potted multiplier failed but that didn't hiss, just no display was visible. cheers Tony

14th Nov 2025, 9:45 pm	#1
Joe_Lorenz Heptode Join Date: Dec 2019 Location: Hohenroda, Eastern Hesse, Germany Posts: 721	Tek 7603 - a quick fix? Hello, one of my sons shoved a 7603 on my bench. It had been sitting for years and upon firing it up (yes, I know ... no good idea) it gave in after half a minute of operation. A hissing noise and a vanishing beam. It seems to be an early one, #100044 according to the manual. As I did not have much time to investigate thoroughly I just did a visual inspection: I could not spot any exploded tantalums or other destroyed capacitors without dismantling - and that does not seem to be such a straight forward job as on my 5-series scopes. Are there any known typical faults, or do I have to proceed methodically? I tend to assume the big electrolytics of the psu might be dried out. Kindest Regards, Joe