To All HIFI Masters,
I would like to ask for your help here. I am helping my friend to fixing up a Myryad MXP2000 preamplifier... the power transformer to the preamplifier board is dead ("open" on primary side, already checked thermal fuse). Myryad has been sold off and I can't find any information about this transformer. I contacted the new owner, but it was sold off again 🙁 I only hope to obtain some info or a service manual!!!
I contacted Talema (the transformer manufacturer)... no success either. No one bother to respond to my emails 🙁
To you All, I would like to obtain the transformer specs so that I can source a replacement from Digikey or Mouser... If you have any information about this transformer, please help. Please see photos attached of this transformer.
Many thanks in advance
I would like to ask for your help here. I am helping my friend to fixing up a Myryad MXP2000 preamplifier... the power transformer to the preamplifier board is dead ("open" on primary side, already checked thermal fuse). Myryad has been sold off and I can't find any information about this transformer. I contacted the new owner, but it was sold off again 🙁 I only hope to obtain some info or a service manual!!!
I contacted Talema (the transformer manufacturer)... no success either. No one bother to respond to my emails 🙁
To you All, I would like to obtain the transformer specs so that I can source a replacement from Digikey or Mouser... If you have any information about this transformer, please help. Please see photos attached of this transformer.
Many thanks in advance
Attachments
I think you will have no choice but to extrapolate from the operating voltage of the power supply capacitors (if they are 25v, you should have about 18 to 21Vdc) which would give you secondaries around 12Vac to 15Vac (this is just an example), ditto if there are secondaries that go to voltage regulators, they will allow you to determine its voltages. Then you have to estimate the power (VA) of the transformer, it's the easiest.
Thank you for your suggestion about working backward from the power filter capacitors... I have been thinking about this too. This will be my worst case scenario right now (if I cannot find any information from the forum...). I thought Myryad was a popular brand name and I was hoping someone here have had a chance playing with these equipment... Also Talema transformer is a popular product too and they have been around for such a long time.... funny enough their website is pretty limited !!! Once again thank you 🙂
Please take a picture of the main pcb (front), it is impossible to find one (in detail) on the net.
Myriad has never really shared a schematic, except for a few old ones, so you have no chance of having more information.
I was hoping for pictures of the printed labels. The label shows useful info re the primary. I was hoping there might be analogous clues for secondarys. 🙂
Are there any recognizable regulators present that might give insights? Do you have any adjustable bench power supplies?
Are there any recognizable regulators present that might give insights? Do you have any adjustable bench power supplies?
Thank you for your suggestion... I will share more photos here... just in case someone will need them in the future. Attached are photos of the preamplifier board. Thanks again
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The power supply filter capacitors are 1000uF @ 35V.
There are 2 main regulators LM317 and LM337. I think there is another 5V regulator (small capacity one), but cannot see clearly unless I have to desolder it
Thank you once again for your help.
There are 2 main regulators LM317 and LM337. I think there is another 5V regulator (small capacity one), but cannot see clearly unless I have to desolder it
Thank you once again for your help.
Are those tho TO220 packages by the fuses regulators? If so what are they. That would give you a good indication for the required voltages.
Those are 2 main regulators LM317 and LM337.
As mentioned, I think there is another 5V regulator (small capacity one), but I need to confirm after taking it off the board.
Thank you
As mentioned, I think there is another 5V regulator (small capacity one), but I need to confirm after taking it off the board.
Thank you
Do yo have a bench supply? If so you can power up the unit and see what the output of the regulators are set at. Usually your AC voltage would be roughly the same as your regulator output voltage to allow for some headroom for the regulators to operate. You can also figure out the output voltage from the resistor values connected to them.
Thank you... my understanding are:
. The max voltage of filter capacitors sit at 35V i.e the transformer's secondary cannot exceed this level
. The 2 regulators are to run 2 voltage rails a +ve and a -ve.
. The 2 regulators are about < 1.5A capable (if I remember correctly)
. I believe there is a safety/detection circuit that switches off the preamp + source switching control (from front panel).
That is all I understand at this point. I can find a power supply at the weekend and try out.
Thank you for your help
. The max voltage of filter capacitors sit at 35V i.e the transformer's secondary cannot exceed this level
. The 2 regulators are to run 2 voltage rails a +ve and a -ve.
. The 2 regulators are about < 1.5A capable (if I remember correctly)
. I believe there is a safety/detection circuit that switches off the preamp + source switching control (from front panel).
That is all I understand at this point. I can find a power supply at the weekend and try out.
Thank you for your help
Op amps will usually powered from +/- 18V supplies maximum. +/- 15VDC or +/- 12VDC are more common. 24V relays suggest +/- 12VDC supplies, but this isn't certain. Keep in mind, transformers don't normally fail without a reason. If the thermal opened it was likely overloaded. You may have more issues.
Thank you... at first I found the transformer open circuit; I opened up the transformer and the fuse was gone 🙁 I was hoping only the fuse went kaput, but then found the primary winding was gone too. I then had a quick multimeter check all the easy access transistors/regulators and found no shortage whatsoever. I haven't checked those ICs and the SMD components yet. I also found 4 capacitors lost approximately 40% of their nominal values (not the main filter capacitors).
I have never thought the preamplifier can pull a heavy load to push the transformer into failure ??? Given this is almost 20 years old product, I ccurrently believe that its transformer died due to aging 🙁 🙁
Myryad has a funny way of designing their products. This preamplifier has 2 transformers... one transformer is to power the front control panel and one transformer is to power the preamplifier board. And for the MXI2080, which is a combined of MXP2000 + power amplifier, there are 3 transformers... the 3rd one is to power the power amplifier board. It almost like adding more components as they go along with the design process...
Thank you for your kind help!!!!
I have never thought the preamplifier can pull a heavy load to push the transformer into failure ??? Given this is almost 20 years old product, I ccurrently believe that its transformer died due to aging 🙁 🙁
Myryad has a funny way of designing their products. This preamplifier has 2 transformers... one transformer is to power the front control panel and one transformer is to power the preamplifier board. And for the MXI2080, which is a combined of MXP2000 + power amplifier, there are 3 transformers... the 3rd one is to power the power amplifier board. It almost like adding more components as they go along with the design process...
Thank you for your kind help!!!!
The multiple supplies is common in "better" preamps. It isolates digital noise from the audio circuits. Power amplifiers run at considerably higher voltage so they often have a separate transformer.
It could be done, but it wouldn't necessarily be cheaper and may not achieve as good digital isolation.
I've never seen multiple voltage output Telma transformers. It may be that they don't produce them.
I've never seen multiple voltage output Telma transformers. It may be that they don't produce them.
Try exploring the link below. Look for a transformer with similar dimensions. This will tell you the likely VA rating. Then select among appropriate output voltages. https://talema.com/transformers-in-distribution/
Is there more than a single transformer? Maybe logic current is modest and drawn from shared positive supply.
If you can sort out resistor values near the regulator adjust pin(s), you’ll be able to derive nominal regulator output voltages and thus needed input voltage.
Be sure to inspect bridge rectifier diodes. There may be a short that led to transformer failure.
Is there more than a single transformer? Maybe logic current is modest and drawn from shared positive supply.
If you can sort out resistor values near the regulator adjust pin(s), you’ll be able to derive nominal regulator output voltages and thus needed input voltage.
Be sure to inspect bridge rectifier diodes. There may be a short that led to transformer failure.
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