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MTX Thunder 2300 board photographs needed
MTX Thunder 2300 board photographs needed
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Old 10th November 2017, 09:28 PM   #41
JonFennell is offline JonFennell
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I have found the problem. When I added the extra solder to increase the current carrying capability I swallowed up the resistor end pin. It's in the center of the image. Looks rather a mess.

I will have to purchase a new resistor and go again.

Transformer of course, not sure why I'm calling it an inductor.

Thanks again. Will try again in a few days.
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Old 10th November 2017, 09:42 PM   #42
Perry Babin is offline Perry Babin  United States
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you can test it without the resistor.
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Old 14th November 2017, 07:15 PM   #43
JonFennell is offline JonFennell
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Hi Perry. I take your point about testing it, but I wanted it fully repaired before that.
I have fully replaced all known parts. All power supply transisters are 3205, and all output fets are IRF540N
My power supply is a battery charger set at 6v, giving 8.8v. It's the best I've got other than a car battery.
I have a red light on.
I have a mid pitched buzzing, from the transformer. A bit too loud for my liking but the board is not in it's case. Sounds more like fat frying.
I have 19 volts on the common cathode diode relative to battery earth and -14 on the common anode
I have all four power supply fets slowly warming up, in about 60s they are hot to touch.
The two on the left get hotter than the two on the right.
All output transisters are cold.

A good start. Concerned about the voltage not being even. I did buy two new rectifying diodes.

Please can you tell what I should do next?
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Old 15th November 2017, 05:09 AM   #44
Perry Babin is offline Perry Babin  United States
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The charger likely has an unfiltered output and will cause noise problems.

In testing, you want to limit the current initially. This can be done with a large resistor, a headlamp (H6054, both filaments in parallel) or by using a fuse (10-25 amp, depending on the amplifier). You also need to clamp all components down to prevent them from overheating and failing.

The shield ground under the RCA jacks is also likely to break on these amps.
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Old 15th November 2017, 09:58 AM   #45
JonFennell is offline JonFennell
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Ah, ok, that makes sense. I used it because it's got a ammeter display so could watch the amp starting up. I did use a lightbulb as you suggest in your guide.

The RCA is good on this amp.
I've bolted down the transistors, still concerned about that imbalance in the power supply. All four transistors were from the same batch.
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Old 15th November 2017, 10:12 AM   #46
Perry Babin is offline Perry Babin  United States
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If you have a scope, compare the drive signals on the gate legs of all of the power supply FETs.
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Old 15th November 2017, 10:42 AM   #47
JonFennell is offline JonFennell
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Quote:
Originally Posted by Perry Babin View Post
If you have a scope, compare the drive signals on the gate legs of all of the power supply FETs.
I don't have a scope Perry.
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Old 15th November 2017, 10:53 AM   #48
Perry Babin is offline Perry Babin  United States
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What multimeter do you have (link to owner's manual please)?
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Old 15th November 2017, 10:58 AM   #49
JonFennell is offline JonFennell
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https://www.clarkeservice.co.uk/manuals2/cdm45.pdf
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Old 15th November 2017, 11:06 AM   #50
Perry Babin is offline Perry Babin  United States
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It's only rated to 400Hz so I don't think it's going to read much but try reading the AC voltage across legs 1 and 3 for all of the power supply FETs. Do they all read the same?
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