Looking for some help with my sx 1050

[Stinkpot75]

After replacing a bunch of capacitors I was checking DC offset on post 4 (like the 10th time) when my clip slipped and touched post 3 too. I thought it just blew the 10 amp fuse so I replaced it. Now I have a fried R1 on the surge suppressor 098 board. I found a replacement for that 3.3 ohm R1, but what else should I look at? What else might I have damaged?

Thanks

 

[Watthour]

Welcome Aboard. !

The AWX-098 soft-start board may have saved a lot of other damage to the unit by sacrificing the resistor when the unit was powered on after the "incident" with the meter probe.

That slip temporarily applied the -60V bus (rail) voltage to the amp output. It would be prudent to check the main amp board left channel emitter resistors R49 through R67, and the driver and output transistors Q13 through Q29. This should all be done with power off.

It would also be prudent to connect the receiver through a DBT to limit line current when powering the unit back on for the first time.

 

[merlynski]

The thermal fuse in series with R1 on the soft start board should have opened and protected R1 when it got hot, long before it destroyed R1. Unless somebody bypassed it, like on this one.

 

[Watthour]

Self-inflicted wounds are the worst. That NTE fuse is about four bucks. The resistor is probably $50. I just don't understand the logic of some people sometimes.

 

[embrown057]

If you need that resistor let me know, I have a few extra.

 

[Stinkpot75]

Thanks everyone. The thermal fuse is open and the resistor still measures 3.7 ohm. The coated wire tied around the two parts is what smoked. I've been looking for the right micro-temp and it seems hard to find a 109C 10A, most I see are 15A 250V. Since this is a thermal fuse I wasn't comfortable with just getting something close. What's a good replacement? They look fine, but I still gotta get in there and measure the parts Watthour suggested. Can the transistors be tested on the board?

 

[avionic]

Thanks everyone. The thermal fuse is open and the resistor still measures 3.7 ohm. The coated wire tied around the two parts is what smoked. I've been looking for the right micro-temp and it seems hard to find a 109C 10A, most I see are 15A 250V. Since this is a thermal fuse I wasn't comfortable with just getting something close. What's a good replacement? They look fine, but I still gotta get in there and measure the parts Watthour suggested. Can the transistors be tested on the board?

Exact replacement.. 109°C = 228°F 10Amp
https://www.alliedelec.com/selco-swtc-228-3535/70098743/

 

[avionic]

Can the transistors be tested on the board?

Not reliably..

 

[avionic]

When resoldering the new thermal fuse onto the board. Clip some kind of heatsink on the lead your soldering. Or solder very quickly . To much solder heat could destroy it.

 

[Stinkpot75]

Thanks avionic, I was wondering about that... just ordered a few of those fuses.

 

[avionic]

BTW welcome aboard stinky..

 

[slow_jazz]

Good luck.

 

[zebulon1]

Another option if you are using Parts Express:
Maybe order a few in case it opens when installing.

https://www.parts-express.com/nte-8...1457483&PID=8158976&SID=jk6xszipyg02ko3q0005c

 

[merlynski]

Another option if you are using Parts Express:
Maybe order a few in case it opens when installing.

https://www.parts-express.com/nte-8...1457483&PID=8158976&SID=jk6xszipyg02ko3q0005c

They are actually readily available for under $2.00 each. I got a bunch of that exact one!

 

[1MEGΩ]

After you replace the thermal fuse, before checking all those components in the amp, save yourself some time and power up the 1050 for the first time using the DBT. I would use a 60 or 75 watt bulb. The DBT will pretty much tell you if anything is shorted in the amp or power supply. If the bulb goes dim, you are probably good to go. But while powered up with the DBT, check the DC offset and bias. If all is good, you should get audio out to the speakers with the volume control set at low volume, around 9 O'Clock position but no higher.

 

[Stinkpot75]

Thanks again for the advice y'all. I'm gonna pull those parts and test them soon. Will have to build a DBT before any power too.

 

[Stinkpot75]

Without removing anything I went ahead and measured R49 through R67 and everything looked good except R51, which was 6k not 18k.

 

[Stinkpot75]

Finally got around to at least checking the left side output transistors. Looks like one bad 539C and one bad 287C. What's the advice here? Find two old ones, or replace all with new equivalents?

 

[merlynski]

My opinion: replace all with new equivalents. New insulators, fresh heatsink paste.

 

[avionic]

replace all with new equivalents?