Car amp repair

[static]

Hi all. I'm new to this type of repair, but I figured I would try. I have an early 90's Optimus car amp that Ive had for 15 yrs and it stopped working. There appear to be a few large capacitors leaking unless its supposed to look that way, and also a mini transformer covered in goop. I have uploaded some images of what I have. Mainly I am trying to diagnose what is the problem before I start throwing parts into it. Any info or help would be much appreciated. Thanks

 

[Heliman]

What appears to be leakage is glue. Very common for manufactures to glue components on before soldering.

 

[static]

Oh. that's good to know. So maybe it is the little transformer thing that went bad.

 

[Bluejets]

Difficult to say...pic is out of focus and too far from the suspect item.

 

[73's de Edd]

Sir static . . . . . . .

That formulation is one of the BETTER glues .

For starters look at the new YELLOW square designated capacitor pair.
With the board now being "naked" of heatsinking.
Use DC voltage reading of metering to be connected across one and then the other "YELLOW" electrolytic caps , for two tests.
Don't power up for more that 5 seconds to get a reading , in confirming that your power supply, over to
the right, is getting DC power over to your amp section at those caps.

After testing and with no power see if any of the pink transistors are dead shorted by ohmmic testing.

Does the PINK star emitter resistor have a crack slanting across it ?

REREFERENCING:






73's de Edd

 

[static]

Thank you for the input. I will try and test it tonight. When you say; "Use DC voltage reading of metering to be connected across one and then the other "YELLOW" electrolytic caps , for two tests" , I'm not sure what you mean. Do I connect a meter to test these caps, and then test with power on then off so as to make sure I am getting power to the caps? Sorry, I'm new at this and even connecting the test leads of my meter is unclear to me. Just set my meter to DC voltage and test for power across each cap with power briefly, then w/ power off test the PINK transistors w ohm meter? or test the caps w/ power off as well? Thanks, and I don't remember seeing any cracks on the transistors.

 

[Bluejets]

Hi Edd,
Can you tell me how you can see a crack in the emitter resistor?
I can't even see the resistor!
I think it must be because you are closer to th image in the US, in Aus we are just too far away.

 

[73's de Edd]

Sir static. . . . . . .

Do I connect a meter to test these caps, and then test with power on then off so as to make sure I am getting power to the caps?

The two caps are the storage reservoir caps for the negative and positive power supplies and the side by side capacitors are sharing their central, common positive and negative terminals.
The very outermost terminals are being the separate positive and negative supply points which then pass over to the power amp circuitry which is using a pair of transistors for each power output channel.

Take metering , place it in DC mode and above 50VDC scale and put one probe on the shared central +&- buss and the other probe goes to the outermost terminal of one cap and power up the system only a few seconds to see if there is a DC reading.

Look at the side spec of the capacitor and do not expect voltage above that number.

Keep the central probe in the same place and move the other probe over to the opposite caps outer terminal for its voltage reading, which would be of the opposite polarity . . . . at ~ the same voltage value..

If you do not get readings, the switch mode power supply, within your RED oval, is having problems.

Did you find any blown fuses ?

If you test the 4 power transistors, that will be done by ohmmeter mode and in a no applied power condition.

The emitter resistors . . .not transistors . . . . are the 4 white bisque ceramic units.
My PINK star was on one that appeared to have a crack sloping across its top . . . .unless that was just being an "optical collusion".

You told us OPTIMUS, but there are different series over a time period, with the full ID number, we might find a schematic floating around .


73's de Edd

Aside . . . . .
fer der Bluejets meister . . . . . .an 'ole F86, 105 and F16 thunderjockey here.
Emitter resistor further clarified above . . . .just awaiting his inspection.