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Author Topic: HH MA150 blowing mains fuses  (Read 758 times)

Enzo

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Re: HH MA150 blowing mains fuses
« Reply #30 on: October 11, 2017, 06:45:16 PM »

Melv
Troubleshooting is a skill, an approach, and it doesn;t really matter whether it is tube or SS you are working on.  Yes or course the details are different, but it is all about isolating the problem.  Once you know WHERE a problem lies, it is usually pretty clear what needs to be done.

CLues are clues, resistors burn up in SS for the same reasons as in tube gear - excess current.

MY point is that you probably know more about troubleshooting SS than you realize.
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Melv1

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Re: HH MA150 blowing mains fuses
« Reply #31 on: October 12, 2017, 04:07:02 AM »

Cool! Thankyou Enzo, that was a bit of a confidence boost, and a clue I think. which are both rather needed in this case  ;). I will get to the bottom of this fault if it's the last bloody thing I do.  :duh
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Melv1

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Re: HH MA150 blowing mains fuses
« Reply #32 on: October 15, 2017, 09:09:37 AM »

Right then, I 've found the short causing the fuses to blow, it was R11 and R13 were shorting where they had been badly soldered.After rectifying this  I Tried the lamp limiter test and this time the bulb flickered for couple of seconds and went out, so all good there. I then turned on full power and no blowing fuses  :tu:. However I have full rail voltage at the output, that's 60vdc. Any ideas please?
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g1

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Re: HH MA150 blowing mains fuses
« Reply #33 on: October 15, 2017, 03:57:28 PM »

Post DC idle voltages for Q6&7, Q1&2.  No lamp limiter.
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Melv1

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Re: HH MA150 blowing mains fuses
« Reply #34 on: October 16, 2017, 05:15:23 AM »

Ok g1, will do.
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Melv1

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Re: HH MA150 blowing mains fuses
« Reply #35 on: October 18, 2017, 07:56:37 AM »

Ok I have read the voltages. Let me just point out there are two different sets of Q1 and Q2 , one set are on the board, and one set are the output transistors and are off board. I put the black lead of multimeter to ground and red lead at the Base, Collector and Emmitor at Q6,7 and Q1,2 (that is the output Q1,2), and all readings are the same at 60vdc. I then put the red lead to Q2 Collector on the board and suddenly R32 burned up and smoked. ???????
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g1

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Re: HH MA150 blowing mains fuses
« Reply #36 on: October 18, 2017, 02:26:26 PM »

Yes, I meant the output transistor Q1&2.
I think you must have had a burst of oscillation probing the Q2 on the board as R32 is a feedback loop component.
You say there is 60V on all those transistors.  I assume you mean positive DC?
Where is your -60V supply?
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Melv1

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Re: HH MA150 blowing mains fuses
« Reply #37 on: October 19, 2017, 08:44:09 AM »

Sorry I forgot to check if it was - or + volts, I think they were all plus but I will check in a mo.
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Melv1

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Re: HH MA150 blowing mains fuses
« Reply #38 on: October 22, 2017, 11:10:54 AM »

Right g1, I've took some more measurements and here they are all VDC
Q6 B=-58 C= +58 E = -58
 Q7 B=-58 C=-58 E= -58
OUTPUTS
 Q1 C=+59 B=-58 E=+58
 Q2 C=-58 B=-58 E=-58.
 I also checked the other transistors
 Q1 B= -10(this was falling with time), C=+59 E=-2(steady).
Q2 B=+59 C=-58 E=+59
 Q3 B+59 C=+59 E=+59
Q4 B=-57 C=-58 E=-58
Q5 B-57C-58 E=58
Also when I touch red lead to Q6 C something smoked around q1,q3,q2,c6 area but was hard to see what component as didn't smoke after that.
Any help would be much appreciated.
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