JCM 2000 DSL 201 blows HT fuse

[jvm]

Hi, guys.I have a Marshall DSL 201 (20 watt) blowing the HT fuse immediately when switching from standby. Filament and -15/+15 supplies are ok. Bias supply -16V. Blows fuse without tubes installed. No visible component damage. Any help appreciated. Schematic can be seen here:Marshall Amps Info & Schematics

[52 Bill]

A quick look at the schematic shows all of the typical things to check. Look for a shorted filter cap, bad tube socket, bad output transformer, etc.

I usually try and trace the high voltage path with my ohm meter. Ground the negative lead and take resistance readings starting at the secondary of the standby switch. Pull the center tap lead of the output transformer and see if the short goes away. If not, try lifting one end of R55, which will remove all of the driver/preamp high voltage circuits. This will isolate the short to the power amp or the rest of the amp. Keep looking until you find the cause of the short.

[jvm]

Thanks, 52 Bill. I started tracing the circuit as you suggested. I pulled the CT first and after I put it back my short was gone! I installed a new fuse and powered up. Amp stayed on until I messed with OT primary wires. Transformer arced. I think I may have found the problem! Any suggestion for a replacement tranny? Hate to pay shipping from England. the stock OT is a Drake 351-626. Thanks for your help.

[52 Bill]

If moving the wires cause the arcing, I'd start by checking the terminals where the wires connect to the transformer.