Marshall jcm 2000 problem

[mispeltyoof]

Amp (JCM 2000 DSL 401) has developed a weird fault: power on light comes on, but valve pre-heater doesn't, so no sound.

Checked the fuses - both fine. Tubes look good. Can't do any more since I'm not confident to discharge the capacitors and avoid killing myself by working on it!

Think it must be cold solder-joints on the PCB or the bri...dge rectifier itself that's the problem. Surprised it didn't blow a fuse when it went, though. Any suggestions very greatfully received

[acorkos]

i've seen a couple of those amps with the same problem...bad bridge rectifier BR102, 10 Amp, 200V

http://www.drtube.com/schematics/mar...60-02-iss9.pdf

[oc disorder]

Have you opened it up and checked the internal heater T6.3 A slow blow fuse?
If its blown they usually go for a reason the output tubes are a prime candidate.

If the output tubes and the pi light up its as Acorkos said "bad bridge rectifier BR102".
This only supplies DC to the heaters for the first 3 tubes.

The search engine here should find some useful information.

[mispeltyoof]

thanks guys I'll look at that . Any idea where I can get this rectifier in UK?
Thanks again for help.

[oc disorder]

Cricklewood Electronics Ltd
40-42 Cricklewood Broadway London NW2 3ET England.
Cricklewood Electronics - CCTV. CCTV Equipment. CCTV Systems. Digital CCTV Cameras

Either of these would do need.. to check the physical size
Part No.: KBPC1010

Bridge Rectifier Radial 10A 1000V. Plastic Body with Centre Hole & Thick Leads. Long Lead Positive
Price: £1.00

Part No.: 608
Bridge Rectifier Radial 6A 800V. With Centre Mountil Hole
Price: £0.60

They can carry much more than required but they're in stock.
RS Components or Farnell carry them in the UK but usually you need to spend more
than a pound !

[mispeltyoof]

Just before I stick my hand into the amp can anyone tell me whether the amp has 'bleeder resistors' or not, please?
In other words do the capacitors "empty" themeselves or will I need to bleed them manually before being safe to touch?

[oc disorder]

The circuit acorkos posted doesn't show any bleed resistors the main cap is c32 so if you're concerned about it I suppose a resistor from the standby switch to ground
500ohms or 1k should do it.
You should be able to measure it between the s/b sw and gnd.
If it hasn't been turned on in a while it may be ok.
To me those kinda shocks are more of a surprise than lethal.
Geeze in Aust we used to get new ones wrap the leads around the body then charge them up and the first person to walk into the workshop bar the tea lady ..
here ...catch !!! Nobody died to my knowledge but in this day and age probably not a good idea !