Myryad MA 240 service manual

[Bix]

Hi all, my amps not clicking on. When I disconnect the power rail the relays click on, but they don’t when connected. DC is fine.

Hoping someone has a service manual? Maybe even help me diagnose the problem.

Thanks gang

 

[huggygood]

to my knowledge, there is no service manual for the ma240.
I am repairing a z140 and the only document I found
and the manual service of the T40 which has a bit of the same circuit.
you'll find it here, you can compare with yours.

MYRYAD SYSTEMS T-40 INTEGRATED AMPLIFIER 1982 SM Service Manual download, schematics, eeprom, repair info for electronics experts

 

[Bix]

Thank you very much, I’ll check it out. The board is well laid out, guess I’ll take my time and test things slowly. PSU seems fine and the relay seems to be doing its job. Visually I cannot see any damaged components.

 

[huggygood]

by experience,check the underside of the pcb,it is very hot under there.
mine is very beautiful above but cooked below

 

[Bix]

Yes, mine was running pretty hot before hand. I’ll take the board and have a look. This will be great learning experience for me I hope. I’ve built a few projects, chip amps, Salas FSP but this will be my first repair. Fingers crossed I can get it working again.

 

[huggygood]

think to write on the forum, I will follow you and answer you as I can

 

[Bix]

by experience,check the underside of the pcb,it is very hot under there.
mine is very beautiful above but cooked below

You called it. Looks like quite a few transistors have burnt out. I’ll have to order a solder sucker today.

 

[huggygood]

check all drivers and all output transistor .
the drivers are realy hard to find but you can replace them with mje 15030 and 15031
the output transistor are commun and really simple to find

 

[huggygood]

also controls the regulated supply

 

[Bix]

Thanks you. I’ll keep you posted. I have to go to work now but will have another look tonight. While I wait for the solder sucker, is it possible to test the transistors while in the board? I’ve only tested with DMM set to diode setting.

 

[Bix]

also controls the regulated supply

I didn’t realise there was a regulator. I’ll go through it all tonight when I have more time, thanks again

 

[huggygood]

DMM set to diode testing or resistance with buzzer (short circuit)

 

[huggygood]

have a good day

 

[Bix]

Ok then, so I’ve ordered a soldapullt. The Ouputs seem fine the bad ones are a1479 and c3789, I’ve found this link 2SA1479 p-n-p transistor complementary npn, replacement, pinout, pin configuration, substitute, marking A1479, equivalent smd, datasheet that has replacement suggestions at the bottom. What would you suggest maybe? I suppose the question is why would they have burned out? Too hot, over powered?

 

[huggygood]

the sa1479 and sc3789 are the drivers ?
you can substitute them with mje 15030 and 15031

 

[Bix]

Hi, my previous order didn’t go through so I’m putting in a new order today. Solder pump, Capacitor for another project FSP, Bnc to crocodile test lead for signal gen, 8 ohm 150 watt dummy loads and new transistors for my busted amp. Thank god for the old chip amp.
So the transistors that need replacing are before the pre drivers, input pairs or something. I’m not sure exactly there function but they are: 2sc3790 D and 2ca1480 D. I’m attaching a screenshot with details.

Any suggestion for a substitute would be greatly appreciated.

 

[Bix]

I found this one at Mouser, suitable? Advice appreciate.

 

[Bix]

Would anyone like to help me save my amp?

I’ve replaced the regulator Q504 - 503, 505, 506. Q501 and 502. Please see pictures, any advice on how to find the fault please.

 

[huggygood]

hi bix
sorry to hear this :/
can you repeat the various operations that you conducted on this amp ?

 

[huggygood]

where are you bix with your myryad ?
i'm on new Z140 with a strange probleme