Rexx RG45 Repair

[mb87]

Hey guys, I have an old amp lying around my place that belonged to my older brother, it has alot of sentimental value to me and I'm trying to fix it. It has a fried resistor. My problem is I cant for the life of me find a schematic of the amp online and have no idea how I would go about tracking down that information? But anyways I have taken a few photos here so you can better understand what exactly it is I am trying to fix. The resistor the was completely fried is R78, and there is some damage done to R77 and R79, so I am going to replace all three. My problem here is R78 is so friend I cant identify the value of the resistor via colour coding? I need some help, what do I do? How do I track down the correct resistor that needs to be replaced? Any thoughts and suggestions would be greatly appreciated.







upload pic

[Enzo]

Resistors do not burn up on their own. Something drew excess current through them. Usually a shorted semiconductor.

All I know is Rexx was a Canadian brand made by a guy from Yorkville.

[mb87]

I mean thing only has sentimental value to me so I want to fix it myself, really dont feel like paying someone to fix this for me, what would be my best bet to identfy what else has shorted, as there is nothing obvious on the board that looks fried.

[Enzo]

It appears to be well made, and a Canadian forum had guys saying how they liked them.

This will be hard. The big square cement resistors would b easy. First thing to my mind is your resistor might serve a 15v zener, which shorted. But that would require close inspection.

[mb87]

It appears to be well made, and a Canadian forum had guys saying how they liked them.

This will be hard. The big square cement resistors would b easy. First thing to my mind is your resistor might serve a 15v zener, which shorted. But that would require close inspection.

Ok so after further inspection I also identified a diode which failed and have since removed, its an N14004

Here are the accompanying pics.



sign image online

[J M Fahey]

I mean thing only has sentimental value to me so I want to fix it myself, really dont feel like paying someone to fix this for me

Unless you have Electronics experience enough to troubleshoot without a Schematic, I fear it´s above your head.

Replacing parts is easy, the task lies in *finding* the bad ones, as you see "sight" alone does not provide enough clues.

Just to give it a try, post a closeup showing those power transistors and parts around them, all labels, colour bands, etc. should be readable.

[mb87]

Unless you have Electronics experience enough to troubleshoot without a Schematic, I fear it´s above your head.

Replacing parts is easy, the task lies in *finding* the bad ones, as you see "sight" alone does not provide enough clues.

Just to give it a try, post a closeup showing those power transistors and parts around them, all labels, colour bands, etc. should be readable.

Well I have some experience with this stuff but its been awhile, I do have the multimeter to read values of each component, anyways ill post that stuff in a bit, just off to pick up a few things, will do once im back, any help is appreciated.

[dmeek]

Please post more photos including all of the foil side and better focus if you can.

[mb87]

[mb87]

it looks like r117 was changed, some work was done that i wasnt aware of, d16 is the diode i just noticed, i also just noticed a resistor was soldered on the back, so something was done, anyways any help is appreciated

[J M Fahey]

Check Q19 and Q20 for shorts, highly suspect.

That amp already suffered a repair attempt, Q19 must have been a TIP142, no Manufacturer will pay U$5.70 an NTE substitution part when the original costs U$2.20
That said, if that NTE transistor is not shorted, leave it there.

[Enzo]

I am still back on R77 (or 78 or whatever the burnt one is) Some of your diodes are marked as Z6 instead of D6, those are zeners. Make sure none are shorted. Also, check at the power pins of the ICs to see if either power rail is shorted to ground.

[dmeek]

Looks like there is a trace connecting the burnt resistor to the burnt diode but the photos of the foil side are still too blurry. Can you switch to a higher resolution on your camera? Component side photos are OK.

There are two round orange components at the input end beside R30 and R107. Are they tantalum capacitors? Check them for shorts.

[mb87]

Thanks guys, just busy at work today, when I get home I will follow all suggestions and will take higher resolution photos with a better camera, thanks so much appreciate it!

[nyota]

hola a todos, tengo el mismo amplificador que mb87 si tienes alguna duda te puedo ayudar