ADA Depot - A Forum To Support Users of ADA Amplification Gear
ADA Power Amps => Microtube 200 MT-200 => Topic started by: deorai77 on January 30, 2018, 06:51:57 AM
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Hi Team,
I have similar issue like El Chiguete, the Ch A works fine . The Ch B fuse is blown, when I replaced the fuse worked but got lose of tone and some volume drops for 1 sec to 1/2 sec coming on and off.
I replaced the tube then worked fine got the tone back the volume drop is gone, then all of a sudden the volume came down like going to mono from stereo. And this is all only channel B as I am only plugged in channel B.
When I bought the amp the transformers was not tightly screwed . But I had tightened it. I wiggled the transformer it made some crackling sound and the tone and volume came back. I wiggled some more , more crackling sound then the volume came down, I wiggled it the volume came back to normal wiggled some more , the fuse blew. What do you recon ?
This is not the same issue as El Chiguete is it? Do you recon its a sort transformer? If so how do I fix it? Thanks in advance guys.
My MT100 has more transistors than El Ch's, pic attached....
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Well if your chan A still works fine, maybe use that instead for now ? MJMP may have some ideas, which trany are you wriggling ?, IIRC the MT 100 has 2, a standard and a toroidal,
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Hi Rnolan, thank you
I was wiggling the toroidal tranny, I got more fuse and placed the 3A fast blow fuse, it popped, I found out that I blew the mosfet as well, now no more sound In channel B, the fuse is blow and the mosfet IRF9530 and IRF530 is shorted . I would like to know what caused that and fix that issue before I replace the mosfet and the fuse.
thanks to replying..
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Don't think the transformer is the problem since both channels share the same power supply. I "think" it might be a bad contact on the pcb since the wires from the tranny are very stiff they might move the pcb also. I would check the soldering on those big white resistors. Sometimes they desolder themself and if you get a bad contact it can blow the mosfet's. Anyway that's what I "think"
But when you replace the mosfet's I would also change the drive transistors and check those signal diodes also.
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Thank you Mr JMP,
Now you meant the rectangle big white 3W resistors right? I will solder it,
Also some to the components are beeping while doing the contenting testing wiht my multimeter.
the 1st from the bottom toward the channel B large 4700uf CAP was beeping like it was sorted out but stoped and now shows reading1 after I removed the mosfet.
but the 4.7uf 50V electrolytic cap next to the L7912ACV still beeps but when I took it off and checked the CAP it seems to be fine,
the gold cap next to the large cap give the same beep.
the 2 gray metal film resistors (think its 2W) next to the large white 3W resistor and large electro 2200uf 35V cap. (but the Channel A side also beeps)
another gray film resistor (think its 1W) next the the channel B tube next tot he brown cap also beeps.
Also the 8099 transistor slepping under a small diode next to the Channel B fuse does not give large reading but only shows 1 on both sides.
Do I need to replace these are is this the effect of the blown mosfet/ normal?
I will post some pictures later today from work.
Thanks Heaps
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Did you set your meter on continuity test? Does it have a diode check test?
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Hi JMP,
Yes, the multimeter set on continuity/diode setting. (has the sideways wifi symbol and diode symbol)
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Measuring in circuit is always difficult and not always acurate. Replace those mosfet's and all the driver transistors (MPSA...). Then it would be best to use a variac to slowly raise the voltage and check the current.