Hi X,
Changed out LED's and checked all resistors before mounting amp board in chassis. Powered up and had about 30 mV at 24 V AC. Adjusted down as I turned up the AC and when full AC, adjusted to around 26mV. Output voltage with no load is 6.2mV. No smoke or any problems, LED's on PS & Amp board are shining brightly. Will test the other channel and report back.
Changed out LED's and checked all resistors before mounting amp board in chassis. Powered up and had about 30 mV at 24 V AC. Adjusted down as I turned up the AC and when full AC, adjusted to around 26mV. Output voltage with no load is 6.2mV. No smoke or any problems, LED's on PS & Amp board are shining brightly. Will test the other channel and report back.
X, tried to power up the first channel that was giving trouble, it was doing the same thing (high mV at low AC) but the LED on the amp board was lit up. I had to shut it down, as some smoke was happening. I checked the PS and everything was good, +/- 48.5V on 110VAC.
So, while I was hooking up the V+ from the PS to the amp board, (0V & V- were already hooked up), there was a spark and one LED on the V- side would not light up anymore and when I checked the voltage, it would not increase. The LED on the amp board does not light up anymore also . Was that spark due to the large caps being not fully discharged?
I will change out the LED on the PS, and then see what the impact is on the amp board. the amp board. Any other ideas that I can play around with?
Thanks,
MM
So, while I was hooking up the V+ from the PS to the amp board, (0V & V- were already hooked up), there was a spark and one LED on the V- side would not light up anymore and when I checked the voltage, it would not increase. The LED on the amp board does not light up anymore also . Was that spark due to the large caps being not fully discharged?
I will change out the LED on the PS, and then see what the impact is on the amp board. the amp board. Any other ideas that I can play around with?
Thanks,
MM
Hi Myles,
Good news on the channel that is working now. You have a model to copy and make sure the other channel is good too.
A spark when connecting amp is from cap not discharging. But also means something was already shorted on amp to draw that much current. Why LED would burn out I don’t know. Where was smoke coming from? Look for discolored resistors or cracked parts.
Usually when that much current flows, the MOSFET is toast. You can check for a bad MOSFET with ohm meter. Between any two pins should be at least in the k ohms not single digit ohms. If single digit it has shorted inside and burned out. May be from earlier reverse Vbe multiplier connection and or bad LED orientation.
Good luck on you debug/repair. These are painful but great learning experiences. I went through this many times before. The variac or safety resistors are meant to protect any damage from excessive current. Sometimes having a 10ohm 10W resistor in series at each power supply input can protect the mosfet from damage if there is a condition that causes excessive current. A variac does not always protect from this. Or a lightbulb in series works too.
Good news on the channel that is working now. You have a model to copy and make sure the other channel is good too.
A spark when connecting amp is from cap not discharging. But also means something was already shorted on amp to draw that much current. Why LED would burn out I don’t know. Where was smoke coming from? Look for discolored resistors or cracked parts.
Usually when that much current flows, the MOSFET is toast. You can check for a bad MOSFET with ohm meter. Between any two pins should be at least in the k ohms not single digit ohms. If single digit it has shorted inside and burned out. May be from earlier reverse Vbe multiplier connection and or bad LED orientation.
Good luck on you debug/repair. These are painful but great learning experiences. I went through this many times before. The variac or safety resistors are meant to protect any damage from excessive current. Sometimes having a 10ohm 10W resistor in series at each power supply input can protect the mosfet from damage if there is a condition that causes excessive current. A variac does not always protect from this. Or a lightbulb in series works too.
Hi Myles,
you should consider making one of these before powering up your next channel.
Powering Your Radio Safely with a Dim-bulb Tester
if anything is wrong in build, Mains Bulb Tester (MBT) will glow brightly and indicate a short, yet your amplifier will be safe.
keep in circuit for initial adjustments of bias also. for testing, you can even play with very low volume on test speaker with MBT in series.
regards
prasi
you should consider making one of these before powering up your next channel.
Powering Your Radio Safely with a Dim-bulb Tester
if anything is wrong in build, Mains Bulb Tester (MBT) will glow brightly and indicate a short, yet your amplifier will be safe.
keep in circuit for initial adjustments of bias also. for testing, you can even play with very low volume on test speaker with MBT in series.
regards
prasi
X,
IRFP240#1: G>D is OL. G>S is OL. D>S is OL.
IRFP240#2: G>D is 000.5 reducing to 000.0 ohm in 1 sec. G>S is 000.5 ohm reducing to 000.0 ohm in 1 sec. D>S is 000.6 ohm reducing to 000.0 ohm in 1 sec.
IRFP9240#1: G>D is OL. G>S is OL. D>S is 10.75 Mohm
IRFP9240#2: G>D is 3. 1 ohm G>S is 3.1 ohm D>S is 000.6 ohm reducing to 000.0 ohm in 1 sec.
Also fried R116 on the AllC's PS. It just crumbled when I touched it. Will have to start by checking out the PS and carry on from there.
Let me know your analyse of the Mfets.
Thanks Myles
IRFP240#1: G>D is OL. G>S is OL. D>S is OL.
IRFP240#2: G>D is 000.5 reducing to 000.0 ohm in 1 sec. G>S is 000.5 ohm reducing to 000.0 ohm in 1 sec. D>S is 000.6 ohm reducing to 000.0 ohm in 1 sec.
IRFP9240#1: G>D is OL. G>S is OL. D>S is 10.75 Mohm
IRFP9240#2: G>D is 3. 1 ohm G>S is 3.1 ohm D>S is 000.6 ohm reducing to 000.0 ohm in 1 sec.
Also fried R116 on the AllC's PS. It just crumbled when I touched it. Will have to start by checking out the PS and carry on from there.
Let me know your analyse of the Mfets.
Thanks Myles
Hi X, Edits to above using my LCR meter.
IRFP240#2: G>D flashes a 27 ohm value then reduces to 0.2 ohms in 1 sec. G>S settles at 0.2 ohm in 1 sec. D>S flashes 1.5 ohm then settles at 0.2 ohm in 1 sec.
IRFP9240#1: G>D is OL. G>S is OL. D>S is OL.
IRFP9240#2: G>D is 3. 4 ohm G>S is 3.4 ohm D>S is 0.3 ohm .
MM
IRFP240#2: G>D flashes a 27 ohm value then reduces to 0.2 ohms in 1 sec. G>S settles at 0.2 ohm in 1 sec. D>S flashes 1.5 ohm then settles at 0.2 ohm in 1 sec.
IRFP9240#1: G>D is OL. G>S is OL. D>S is OL.
IRFP9240#2: G>D is 3. 4 ohm G>S is 3.4 ohm D>S is 0.3 ohm .
MM
Hi X and other builders,
I am rebuilding an All C's PS. While checking components on board, I discovered that C132 (0.022 uF) would not give a reading. I removed the cap and checked it, and it tested perfect. Resoldered in place and could not get a reading.
I tried this twice and had same results. Do you think I may have a pad problem or a trace problem. All the components around C132 test OK.
Myles
I am rebuilding an All C's PS. While checking components on board, I discovered that C132 (0.022 uF) would not give a reading. I removed the cap and checked it, and it tested perfect. Resoldered in place and could not get a reading.
I tried this twice and had same results. Do you think I may have a pad problem or a trace problem. All the components around C132 test OK.
Myles
Thanks for the help,
bullitstang, the board is not live. I tested every film cap with my LCR meter and got accurate measurements, except for the cap mentioned.
Vunce, yes I read that post. I soldered a 0.22 ohm 5W resistor to the outside pads of R115 & R116. No bridge required if using a resistor. This worked fine on the channel that powered up properly.
On the channel that did not power up properly, I have a short that i must find.
First, I wanted to get my PS working, then find the fault in the amp.
MM
bullitstang, the board is not live. I tested every film cap with my LCR meter and got accurate measurements, except for the cap mentioned.
Vunce, yes I read that post. I soldered a 0.22 ohm 5W resistor to the outside pads of R115 & R116. No bridge required if using a resistor. This worked fine on the channel that powered up properly.
On the channel that did not power up properly, I have a short that i must find.
First, I wanted to get my PS working, then find the fault in the amp.
MM
Hi X,
I am thinking of using the N-BJT helper board with the BD139 transistor. Is the 1 on the right side of the N-BJT helper board the place where the 1 (emitter) of the BD139 should attach?
If this above is correct, can the three horizontal holes at the bottom of the helper board
be connected to the amp pcb to complete the connection.
MM
I am thinking of using the N-BJT helper board with the BD139 transistor. Is the 1 on the right side of the N-BJT helper board the place where the 1 (emitter) of the BD139 should attach?
If this above is correct, can the three horizontal holes at the bottom of the helper board
be connected to the amp pcb to complete the connection.
MM
Hi Myles,
The BD139 needs to mount on top of one of the MOSFETs as a temp a sensor. Simply use it like a washer and clamp it between the bolt and the top of the MOSFET. Either one works but I think I used the N channel. You don’t want to mount it separately with its own board. Or are you asking can they helper board give you better connections to flying leads? In this case it’s so small I would solder directly and apply shrink tubing over the legs.
The BD139 needs to mount on top of one of the MOSFETs as a temp a sensor. Simply use it like a washer and clamp it between the bolt and the top of the MOSFET. Either one works but I think I used the N channel. You don’t want to mount it separately with its own board. Or are you asking can they helper board give you better connections to flying leads? In this case it’s so small I would solder directly and apply shrink tubing over the legs.