Print Page - Marshall VS65R no -15V

Title: Marshall VS65R no -15V
Post by: Psabin8951 on July 28, 2025, 12:33:29 PM

I have a Marshall valvestate VS65R combo here it was making lots of loud buzzing even with volume at zero. Caps have now been replaced and I now get clean sound from power amp but no sound through pre-amp. Caps around ZD1 and ZD2 have been replaced with matching parts and as board have clearly got hot there, ZD1 & 2 replaced with 5W 15V zeners. I'm seeing +15V across ZD2 but only -2.86V across ZD1
Any thoughts what will be keeping this low instead of -15V?

Title: Re: Marshall VS65R no -15V
Post by: J M Fahey on July 29, 2025, 06:55:28 AM

Quote from: Psabin8951 on July 28, 2025, 12:33:29 PMCaps have now been replaced .... Caps around ZD1 and ZD2 have been replaced ..... I'm seeing +15V across ZD2 but only -2.86V across ZD1
Any thoughts what will be keeping this low instead of -15V?

Either that Zener or its matching electrolytic were inserted the wrong way. Recheck that carefully.
That cap goes with *positive* to ground.
Please post results.

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Solid State Amplifiers => Tubes and Hybrids => Topic started by: Psabin8951 on July 28, 2025, 12:33:29 PM