Soundcraftsmen T6002

[clearchris]

Hello.

This project has been on the back-burner for maybe two years because it was way out of my skill level. Perhaps it's worth another look.

Soundcraftsmen T6002 AM / FM Stereo Rackmount Tuner

This is the most well put together piece of electronics I have opened. Top cover comes off, exposing a very well documented (printed, have no service manual) pcb with lots of jumpers for testing and adjustment. Bottom cover comes off for soldering the underside, while the frame stays in place. Old enough to still be hand-soldered and use proper Pb solder.

Symptom: When the stereo / mono switch is in stereo position, a fuse will blow. Otherwise, operation is fine. Before I narrowed down the behavior, I completely recapped the power sections. I avoided recapping the rest of the board for alignment issues. Radio probable needs an alignment anyway...

So, I know the stereo button leads up to the stereo section, and the stereo section drives an LED. Otherwise, I'm not sure of the interaction of the HA12016 chip

What do you guys think would be the best first steps here?

1. Obtain a variac and slowly bring up the voltage while checking for a short?
2. Alignment be damned - replace the caps in the FM Stereo section!
3. ???

Picures in next post.

Thanks!

[clearchris]

Re: Soundcraftsmen T6002






Whole board view:


Fuse section. The fuse on the right keeps blowing. Btw, what are the fuse mounts on the left called? I need to add them to the fuses on the right.


FM stereo section. What are the clear and silver components with the black glue on them?

[redwire]

Re: Soundcraftsmen T6002

That's a nice old beast. Check the power supply +13.7V by C147 is within spec.
Does the fuse blow if you are tuned to no station, and then hit "stereo"? (=stereo indicator off)

I've seen a stereo indicator lamp shorted but you have no dial cord...
I guess pin 9 on HA12016 connects to the fluorescent display. I'm thinking the display has a short, if the fuse pops when it lights.

The silver parts with black glue are polystyrene capacitors.

[clearchris]

Re: Soundcraftsmen T6002

Going off memory here, but IIRC, the fuse would blow within a day of the stereo button being selected. It wasn't immediate. This should be easy to test though, I could remove a jumper that links the FM stereo chip to the VFD.

[delaware74b]

Re: Soundcraftsmen T6002

I am seeing a lot of the yellow glue beginning to degrade in your third and last photos. It's turning brown, which does make it conductive. The worst glue I am seeing is at the ends of the ribbon cables and the transformer wires where they are attached.

I had a bad power supply in a HP EVO DC5100 mini desktop computer. Blew the fuse when plugged in, that yellow glue was brown. The power supply was FULL of glue, everything was covered. Took me 3 hours to get all that @%$ glue off the board and components. Glue removed, power supply was fine so I recapped it and it's been running 24/7 for 2 years as a fire/EMS scanner channel feed to broadcastify.com.

[clearchris]

Re: Soundcraftsmen T6002

Wow, i hadnt considered that.

Any thoughts on heating it with hot air then scraping? Maybe soften it up some...

[delaware74b]

Re: Soundcraftsmen T6002

I toughed it out and scraped/chipped the glue at room temperature. Probably why it took me so long.

[clearchris]

Re: Soundcraftsmen T6002

I accidentally left it on overnight. No fuses blew.

Today I removed what I'm calling "the glue transistor".



I used the hot air station ar 120C to heat the glue and it came off relatively easy.
Ill probably solder the jumper back on and see if it blows any fuses.

Unfortunately, the test conditions are not the same. I was downtown within a mile or two of most stations, but I moved farther out. So I might not br getting a good enough signal to light the stereo vfd and blow the fuse. Also I notice the alignment is totally hosed, I think the front end needs adjusting.