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i have a very nice vintage DBX BX3 amp on which at least one channel fused.
power transistors literally burned down.

it is a very nice piece of hardware (4 channels with BTL capability 4x125W or 2x300W)
I would like to fix it myself. Having an electronic engineering degree, i think I should be able to undertake that venture but I never practiced (i've been in software for the last 40 years...)
So I need some guidance on the methodology to diagnose and track what went wrong.

I do have a scope, signal generator and I guess all required tools, as well as the schematics of the amp.
what I need is some help on locating the key parameters to measure and how to incrementally explore the different stages of the amp to find the faulty sections.

I guess I need to isolate the different sections of the amp but then, what ?

any help and advice will be highly appretiated.

 

When the speaker is connected to the 220V network, a hum appears in the bass speaker after 1-2 seconds. There are no buttons that do not work, the red power-on LED is constantly on. What is the reason, where to look for the fault?

Sziasztok! Szeretnék alaplapot cserélni a film nézős számítógépemnél, a legnagyobb probléma az jelenleg, hogy a régi alaplapon RCA koax sdpif kimenet volt, amit a házimozi erősítőre kötöttem. Az új alaplapon csak optikai spdif kimenet van, ugyan az erősítőn van optikai bemenet, de fény szálam nincs hozzá. Nincs valami fiókból összedobható SPDIF átalakító, ami csak a ,,közeget'' alakítja át? (tehát nem D/A átalakítót akarok)

Hello, I am in the process of repairing the Mackie ProFX12 V2 mixer for a client, and am running into the unavailability of schematics. Does anyone have a copy they could share? I have already reached out to Mackie directly but am still waiting for a reply.

Additionally, I am having trouble identifying the failure mode for the two channels that have failed: one produces loud static (indicating bad op-amp or feedback resistor perhaps?) and the other has the right channel producing a 60hz hum, the other is functional. (see board photos, with the two failed channels being marked with "F". The browned area is residual flux from having replaced two opamps, and having reflowed other components around them)


Any help on either of these fronts would be invaluable. I have mainly worked in laptop and computer repair, and am just getting started with my first scope and first set of board level repairs.