Inkel MA-620 Schematic

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First of all thank you for the service manual. From a quick look at the schematic it it is quite different from the MA-620 (which mrfeedback was asking for). I have an original service manual and will scan and send it to you(or post it here) once I´m finished with moving to my new flat. (Currently it´s somewhere buried in a box). Will take 10 days or so.
 
Schematics

I eventually found my MA-620 schematic. Attached is the part with the main
amplifier board.
If you need the complete schematic or higher resolution you may download
it here: Index of /ma620
 

Attachments

  • ma620_2.jpg
    ma620_2.jpg
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sorry to bring this back from the dead ......


It is very well known around the PA people that most of INKEL and earlier Inter M amplifiers are notorious for shelf destroying or generally destroy any speaker connected on them ..

I dont really think that there is any operative MA 620 as we speak but just in case here is the info :

At the MA 620 the pcb designer skipped or failed to design a proper vbe multiplier attached on the heatsink...The related parts are located on the pcb ...combine this with the poor ""natural "" cooling, the only vent exists in the device will ventilate the inside of the amp while the transistors will dissipate heat only from the quite big heat sink .... that is thermal run away

Now think ... the ventilator will cool down the inside of the amplifier ...the pcb, the vbe multiplier and while the vbe multiplier will think that the amp is cool will eventualy increase the bias while the output stage will be in a boiling status ....Double thermal run away .

Please replace Q109 R,L with a BD 139 use 3 leads of cable and attach firmly in any existing screws of middle output transistors .....

Adjust for 10mv over 0.27 ballast resistors

Expect the suggestion to preserve a very stable bias and start to decrease in a marginal level for distortion around 70 degrees on the heat sink but one way or another at this temperature the double safety thermostat will shut you down .

Kind regards
sakis

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