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 Post subject: Mark IV model B problem
PostPosted: Thu May 03, 2012 11:18 am 
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Bottle Rocket

Joined: Thu May 03, 2012 10:42 am
Posts: 12
After blown fuse, some parts around 10000uF/16V and a couple resistors and diodes,
blown and a part of board burnt. I think here is DC voltage for first tube and 5V regulator. I found on net some schematics but all are for A model. Can I find it or does somebody have it to send me by mail. Image
Thanks in advance
Duka


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PostPosted: Thu May 03, 2012 1:28 pm 
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Road King
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Location: Korn's Bakery Brooklyn NY
If it's R123 thats bad, it's the dropper resistor parallel R401 to the plate voltage when in R1 and R2.

That cap and VR are for the footswitch, or low voltage circuits.

PM me you email address and I will gladly send you a IVB schematic, but my opinion is that you should send the amp to Mesa. Those PCB's are really touchy when it comes to repair.


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PostPosted: Thu May 03, 2012 3:01 pm 
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Bottle Rocket

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PM sent!!!
Thanks


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PostPosted: Fri May 04, 2012 10:36 am 
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Road King
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Location: Korn's Bakery Brooklyn NY
After looking at the photo some more, a blown power tube or burned out power tube could have spiked through the heater circuit and blew the diodes, resistors, caps and the voltage regulator.

Let me know if you have heaters to the V1 and if the footswitch and LED's light up when you power the amp on. Do not turn the amp off standby.


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PostPosted: Sat May 05, 2012 1:33 pm 
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Bottle Rocket

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Boogiebabies wrote:
After looking at the photo some more, a blown power tube or burned out power tube could have spiked through the heater circuit and blew the diodes, resistors, caps and the voltage regulator.

Let me know if you have heaters to the V1 and if the footswitch and LED's light up when you power the amp on. Do not turn the amp off standby.

One 470 ohm on power tube are blown. I check voltage 12VDC and 5VDC and it works. Why tantal C431 - 15uF (I dont know voltage) Q6 -2N6426, R107 -100ohm resistors and 39ohm wired to LDR 27 gone and pcb I diont know. Too when pcb fired I lost 12VDC to LDR's. Heater 12V for V1 works!!! It seems to be problem in circuit (LDR 100K 2N5401) to drop voltage for Lead and R1 and R2.
Maybe to omit this circuit and then check
Thanks


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PostPosted: Fri May 11, 2012 11:33 am 
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Road King
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A power tube blew and took out the ground reference resistors for the heaters.
The V1 has it's own DC circuit. V2-V9 use AC for the heaters.


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PostPosted: Fri May 11, 2012 10:28 pm 
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Mark II

Joined: Thu Jul 22, 2010 5:49 pm
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Just an observation that may be relevant:- Older tube amps used to have a mains fuse which was slo-blo and quite high rating 1-2 amps, but they also had an High Voltage fuse (or one fuse per power tube pair) that was quick blo and much lower rated at 1-200ma. That seems logical to me as a non expert because the mains fuse has to take all the current for heaters, fan, switching, +audio and has to withstand is a big inrush current due to cold tube heaters and capacitor charging, so it seems that it could not be very sensitive to a single tube failure. I thought that the hv fuse was fitted so that a tube failure blows it very quickly protecting the other components. When I see sad photos of holes blown in pcbs due to a power tube failure I wonder whether an HT fuse would have prevented that and why Mesa dont fit them on any amps. Does anyone know why this protection is left out? Much as I like the build quality of my Boogie amps, Mark series especially, I dont know why the HV fuse is never fitted. It seems to me from this forum and other experience that on a Boogie a 'routine' power tube failure is quite likely to result in component failures on the pcb which doesn't seem right to me.

Hope the amp is up and running very soon!


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PostPosted: Thu Jul 05, 2012 4:43 am 
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Bottle Rocket

Joined: Thu May 03, 2012 10:42 am
Posts: 12
Hi
I solved some problem and amp works. Here is problem. I think some switchig parts
are gone. First some vactrols didnt make switching. Because I am not sure, how to check
this VTL5C9 and is possible to find some data of voltages to be sure.
Power tubes works and preamp too. I think, everything is OK except channel switching.
Thanks in advance!!!
If someone ask why I didnt send amp in Boogie service. I havent much money and shipping would be expensive (+ service). For this price I can buy some second hand amp in good condition.
Duka


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PostPosted: Tue Jul 10, 2012 7:19 am 
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Bottle Rocket

Joined: Thu May 03, 2012 10:42 am
Posts: 12
Nobody knows????


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PostPosted: Tue Jul 10, 2012 9:30 am 
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Road King
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Location: Korn's Bakery Brooklyn NY
http://www.datasheetcatalog.org/datashe ... /VT500.pdf

Page 60.


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PostPosted: Tue Jul 10, 2012 9:33 am 
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Road King
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Location: Korn's Bakery Brooklyn NY
Boogiebabies wrote:
http://www.datasheetcatalog.org/datasheet/perkinelmer/VT500.pdf

Page 60.


Easier to replace than to check IMO. Problem is that the IV has 21 or so......


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PostPosted: Tue Jul 10, 2012 12:38 pm 
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Bottle Rocket

Joined: Thu May 03, 2012 10:42 am
Posts: 12
Boogiebabies wrote:
Boogiebabies wrote:
http://www.datasheetcatalog.org/datasheet/perkinelmer/VT500.pdf

Page 60.


Easier to replace than to check IMO. Problem is that the IV has 21 or so......

Thanks!!!
I check today. It seems to be that all LDR's on Lead trace are gone. Other (in R1 and R2 trace) have some ohmage when is in R1 and R2 position. Maybe all LDR's from 19-26 are not OK because noone show impedance in all of three position in Mode select switch. Too, I havent logical show on-off LED on R1, R2 and Lead channel when I switch. Some position on back swiches Loop assign change it. Please excuse me if my english is not good.
One more time thanks.


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PostPosted: Thu Jul 12, 2012 1:30 pm 
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Road King
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Joined: Sun Jan 30, 2005 5:07 pm
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Location: Korn's Bakery Brooklyn NY
I dont know how much help resistance in the circuit will help.

Try continuity (Beep Mode) and voltage. See if you can make a connection from Q6 to D3, then D3 to LDR 26 then LDR 26 to R312 and finally R312 to ground for +12V. See Page 9 of the schematic.

Also, using an LED flashlight with a flexible neck may help you get under the PCB to see if you have a broken trace under the board.

All I can say is that this is not fun and hopefully persitence pays off.


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PostPosted: Sun Jul 15, 2012 9:45 am 
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Bottle Rocket

Joined: Thu May 03, 2012 10:42 am
Posts: 12
Boogiebabies wrote:
I dont know how much help resistance in the circuit will help.

Try continuity (Beep Mode) and voltage. See if you can make a connection from Q6 to D3, then D3 to LDR 26 then LDR 26 to R312 and finally R312 to ground for +12V. See Page 9 of the schematic.

Also, using an LED flashlight with a flexible neck may help you get under the PCB to see if you have a broken trace under the board.

All I can say is that this is not fun and hopefully persitence pays off.

Thanks for reply!!!
I check traces in this part of circuit and it seems to be OK. I solved one of broken traces and I have 12VDC voltage on R312 and others who are in connection with LDR's from 18-27.
Best
Duka


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PostPosted: Thu May 23, 2013 11:00 am 
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Bottle Rocket

Joined: Thu May 23, 2013 10:57 am
Posts: 1
Boogiebabies wrote:
I dont know how much help resistance in the circuit will help.

Try continuity (Beep Mode) and voltage. See if you can make a connection from Q6 to D3, then D3 to LDR 26 then LDR 26 to R312 and finally R312 to ground for +12V. See Page 9 of the schematic.

Also, using an
LED flashlight with a flexible neck may help you get under the PCB to see if you have a broken trace under the board.

All I can say is that this is not fun and hopefully persitence pays off.

I also using a led flashlight but I got it form by sis as a birthday gift :-)


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