RF T20001bd: Keeps blowing fuses.

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I know there are people out there who know these amps in their sleep, and I really hope someone can give some of their valuable time to help me.

I have a RF T20001BD that just stopped working one day. I bought it secondhand a few years ago.

I removed it from my car, and I heard components rattling around in there.

Since it's old, and out of warranty, I took the top off, and found that both c441 and c462 had come off the pcb, (metal film caps) the screws for the fan were loose, and lots of the solder joints looked crusty.

I got the schematics for the amp, and found the specs for the caps, ordered new ones, and soldered them to where they should be.

Then I refreshed the solder joints on the components that are not smd, and I put the amp in my trunk next to my second battery.

Now I connected just power to my battery (with fuses).

so far so good.

Then i connected the remote to the B+ with a small wire, and after about 3 or 4 seconds the 250A ANL fuse was toast.

Nothing (except a growing pile of ANL fuses) looks burnt, nothing smells burnt nothing look fishy, no swollen electroltics or visibly burnt smd components.

Can someone please help me?

I have a DMM, soldering equipment and precision screwdrivers and such, but no scope.

Any input and/or help would be very much appreciated :)
 
Update

I removed the bottom plate and had a look at the bottom of the pcb, and it looked like there was dirty water dried onto the board.

There was also some corrosion from flux, thermal paste and other gunk. The corrosion shorted some of the transistors and rectifiers on the bottom side of the board.

I decided to clean it all up with 96% alcohol and an old toothbrush. Now I'll need to find the spec sheets for the transistors so I can see which legs to measure.

I'll need to reflow the solder joints which are corroded away by all the gunk too.

Added a close up picture of the corroded solder joints.
 

Attachments

  • 20170104_135531.jpg
    20170104_135531.jpg
    459.8 KB · Views: 73
Have you put a meter on any of the outputs or power supply FET's yet?

Measure them gate to source and post your readings.

If you have the board removed you will have to go from gate to ground terminal on the amp for the power supply FET's. With all the ground screws removed the source will appear open.
 
From left to right

Leg 1 = gate
Leg 2 = drain
Leg 3 = source

This amp uses IRFP3415 for the outputs. Half of the devices are audio output and half are rail switchers.

If you have any bad power supply FET's, I always use IRFP064N with 47 ohm gates as a replacement and have never had an issue.
 
What helped me grasp simple output/power supply fet checking some years back was using the meter in diode check(continuity should be okay also for initial testing because I think they only hold a beep if under 100 ohm resistance)If any combination of 2 legs and the meter held a beep and not a quick on/off beep then you likely have a shorted fet or driver etc.And that would quickly give you an idea without generally looking at the meter to read it.
The rectifiers which can look identical to the other heat sink mounted components like stated above can't be generally tested that way especially if there leaking and not shorted and would certainly need removed if suspect to check.They fail much less often than ps/output fets but it surely happens.
I assume you know what where the rectifiers are?Unless there an odd # you can easily google them to verify the polarity or general ID of them.

If you have any shorted outputs,remove them all and focus on making sure the power supply is working.Im guessing you have shorted ps fets and if so,remove all of those.
Oh and save yourself the misery and don't just "add" solder to any questionable joints.Remove old solder first assuming u have a solder vacuum of some sort?Then resolder because a shotty joint could frustrate you till you give up and lose any confidence you may have had.If you only have the cheap solder sucker from radio shack then you should stop and order the edsyn soldapullt ds017 I believe??Inexpensive and invaluable.Order immediately if you plan on doing any repair that's more than a fuse change...lol well a bit more than a fuse change...You get my drift

If you understand most of my little story then your on the right track.Once you have the basics and get down to technical questions without hopefully needing a scope.Perry will likely help you with amp specific issues.

Ps,plan on having issues and frustrations with many through hole component vias and hole clearing if you don't have a good iron also.If you haven't used a good iron before and only $20 radio shack irons.Your seriously missing out on how easy this type of work is with legitimate equip.
You should buy Perry Babins tutorial(links above).It starts from very basic and recommends everything you will ever need(the price is peanuts compared to the info he provides).Past the basics,help on the forum gets much easier.Most people don't have time or can't start from the beginning.Way too much involved generally.So it's tough just starting but obviously various people here have done it.

Frankly this may be my longest message....if you only care about getting that one particular amp working with no desire to learn how to fix them or learn how they work.You may be better off sending the amp out instead of spending X$$ and any possible equipment and parts and obviously no guarantee that the repair will be successful.

Read the basic amp repair page twice even after you think you understand it.All of a sudden it'll click.Just a little effort.
Sorry if I killed your spirit,Just read,tinker and read more.
Jon
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.