Need schematic for Alesis gigamix 4 cd

[fredcapo]

This is a low end powered mixer with a built in cd player. Preamp out is ok but nothing from power amp. Nothing looks burned and transistors test ok in circuit. A scnematic would help. Thanks.

[doctor]

This is a low end powered mixer with a built in cd player. Preamp out is ok but nothing from power amp. Nothing looks burned and transistors test ok in circuit. A scnematic would help. Thanks.

Here is the power amp schematic.

[fredcapo]

Thanks doc.

To follow-up, in general, what is the prevailing wisdom as to repairing equipment of this type? This unit has a number of smaller circuit boards. Are boards typically available from the manufacturer at a reasonable cost to faciltate repair?

[doctor]

With regards to boards, you need to address to local authorized service.
As a rule, such companies do not sell spares directly to users.

[Jazz P Bass]

Alesis is not very good at supplying parts, let alone complete boards.

[fredcapo]

Thanks for the info. I am doing this work for a music store that may have a relationship with Alesis...I will need complete schematic at least to go forward on this.

Anyway when I made some initial measurements, I get +/- 61 vdc on the collectors of the output transistors, where the rails are shown as +/- 48 on the schematic, 0 vdc on base and emitter, AND the mother of all arcs when I discharge the rails to ground after powering off.

So, is the overvoltage just a symptom of nothing conducting...or other problem

and why are caps not bleeding-off... (same reason?)

Thanks.

[fredcapo]

Hey Doc. Can you please post additional pages of the alesis like power supply and perhaps a layout if available.
Thanks.

[doctor]

In what boards you have additional problems?
Layout of what boards you really need?

[fredcapo]

alesis

In what boards you have additional problems?
Layout of what boards you really need?

Doc. The layout of the unit is difficult to follow. I am having a problem identifying test points, signal sources and reference voltages to help me identify a point of failure. I described the condition observed on the power amp board in the above post and no one on this board has provided a comment. My approach would be to isolate and test the power supply and to trace the audio signal to the point where it is lost. I have not yet tried to contact Alesis. Also is it questionable if replacement parts could be identified since they appear to use proprietary markings, and the replacement value of this unit is pretty low. Thanks.

[fredcapo]

Contacted Alesis and they refused to supply a schematic. The mixer was sent to us for repair with other equipment by a very large school district here in Morris County. We made a point of suggesting to them that they refrain from any future purchase of Alesis equipment, except we didn't exactly use the word equipment...