ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Dear members,
My main fuse T 2.5 A is blown after I turned on the swich for the second pair of loudspeakers, although there was no set of loudspeakers attached to the second port. The overload signal was burning for a short while and after 2 seconds there was a complete shutdown. One of the main fuses was blown.
Before I replace the fuse, can any of you bright members tell me what can be done to repair this. I know I have little information at the moment.
I replaced the fuse OF 2, but as soon I powered it up, it blew again, without switching the BM on. Could it be the 2 large capacitors OC8 & OC9 of each 10.000 uF ?
Firstly, rig up a Dim Bulb Tester - google.
Then replace your fuses.
Connect the machine via the DBT, and as long as there is a fault, the bulb will illuminate, and the fuses will NOT blow.
Saves you a lot of aggro this way.
Then start measuring voltages around the big power transistors on the rear panel,a nd compare them to the Schematics.
You'll figure out quickly where the problem is.
I doubt that those big caps are responsible - you can measure for 35V across each one.
You can also follow my recent BM4400 Power Amp Faults thread - but that does NOT mean that my problems are also your problems. It's still in progress at this time.
Menahem
Did the fuse blow BEFORE you powered on the Beomaster ?
Martin
Hello Martin,
Yes, they blow before.
Hello Menahem,
Thank you for your advise. I follow it up.
That's strange because the power switch comes first - then the fuses and transformer.Could be that the power switch is at fault, not switching off. I've seen that before.But there will still be another reason for the blowing fuse.
Is it a type 2317 or a US version (round mains voltage setting switch at the back or not)?Are the fuses correct type and rating?
It's the European version with voltage setting. I have to correct myself, the fuse blows when the power in switched on, but I only get 68 volts (70 volts normal ?) over the rectifier at 240VAC Is this correct?
Are you measuring on the input or output side of the rectifier (is that 68-70V AC or DC) ?
It's the output ( input 240 VAC, output 68VDC)
Sorry, Input 52 V
Doesn't sound all wrong.Does the fuse still blow when you switch speaker set 2 on? Anything connected to those sockets?
OK that sounds good.
Yes the fuse stiill blows. I think I found the problem a transistor shows some black smoke residu around the pins on the board. This transistor is connected with the power transistor(s) for the right channel.
It's TR219 (connected to signal transformer 0TR200)
Sounds like oxidation, thats quite common and usually not a problem unless the components pins are eaten away.
Check whatever is connected to the speaker set 2 sockets. Disconnect it and try running the Beomaster without it.
Check the socket wiring and solder tags for shorts.
Thank you. I'm a couple of days away.
I'm back from a short holliday.
I cheked the transistors today. It seems TR219 has made short There was no noticeable oxidation at the pins, but very tiny burn marks at the board (base and collector). These 2 have a direct connection to 0TR200 (signal transistor), which seems to have made short with the heatsink.