Electronics > Beginners
Beginners Road To Repair Part 2
<< < (3/7) > >>
onesixright:
Hi!


Sent from my iPad using Tapatalk
Shock:
I recommend you move this post to the repair section of the forums.

Obviously be careful with a live circuit could be any voltages present. In the manual it states that the constant flashing is a amplification self test failure. It puts the unit in some kind of safe mode. I would test the op amps and transistors. Won't hurt to check the different power rails though especially if there is +/- for opamps and the logic supply.

There is a gain control pot as well you might want to measure where it was set at and then lower it so see if it makes any difference as well as apply an input signal. If you need a cheap floating audio signal source you can buy cheap Chinese function generators on ebay starting at about $10-$20.
Shock:
When I see big wattage resistors the first thing I look for is dry solder joints and I can see there is a possible dry joint there. If in doubt give them a reflow and ensure you have a low ohm path on any trace that connects to them.

The transistors and regulators on the heatsink can have insulated screws so make sure you keep track of what one was used where. That is a good early lesson to learn that because something is on  a heatsink doesn't mean it's meant to be electrically bonded to it. Heatsinks on many devices are a touch hazard and aren't always safety labelled.

That heatsink looks like it might be attached to the chassis. You can test this though to be sure and if other parts of the circuit that look like they should be are in fact properly connected.

The two electrolytic filter caps have plastic disc covers that often warp as the plastic shrinks a little. Nothing too concerning if the feel flat when you push them down.
don@cascadefellowship.org:

--- Quote from: tpowell1830 on October 02, 2018, 08:35:15 pm ---Hi Don, the big electrolytics on the lower right in the first pic seem to have bulges on the top, can you verify?

--- End quote ---

Sure.  It's possible that the one furthest to the right might have a minute bulge.  Very, very small though.  Here's a pic with the straight edge of the frame as a reference.
don@cascadefellowship.org:

--- Quote from: Wimberleytech on October 02, 2018, 09:12:19 pm ---I use solder braid but if you buy the cheap stuff...it is crap.

You will know if there is an issue with the caps once you measure the supply voltages.  This appears to be a linear supply, so a leaky or high ESR cap is unlikely to be the killer.

Can you provide the IC part numbers? Cannot read them from the pictures.

--- End quote ---

You bet. 

IC 6-8 LM324N

IC 1 & 3 TL074CN

IC 4 LM13700N

IC 2 TL072CN
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod