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Soundstream TRA 1000.2 help
Soundstream TRA 1000.2 help
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Old 5th November 2017, 02:38 AM   #1
dukmang is offline dukmang  United States
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Default Soundstream TRA 1000.2 help

New member here. I have a TRA 1000.2 I'm attempting to repair. It belonged to a friend that passed earlier this year. He had given it to me because I'm an electronics geek, and figured if anyone could fix it, it was me. It got put on the back burner and recently have I been motivated to fix it.

It was a mess. The power supply fets were visably blown along with one of the PNP driver transistors. With help from Perry's repair tutorial I also realized that the burn under the driver was conductive and needed to be excavated. Also Q4 is barely passing current, replacement on order. 3525 replaced and functional when shorting B+ through Q4.

The area where I need some assistance is U3. I don't have a source for a schematic so I'm not entirely sure what its function is but two nearby resistors were overheated. R69 (Ha!) got hot enough to melt the solder and slide off one pad and R8 is completely missing from the board.

I'm looking for the value of R8 if anyone can help. I'm also curious what value DZ1 is since its nearby the missing resistor and needs to be confirmed. Any insight on U3 would be helpful since it doesn't look to be in the input path like the other opamps nearby.
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Old 5th November 2017, 03:20 AM   #2
Perry Babin is offline Perry Babin  United States
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Contact SoundStream Monday to see if they will send you the diagram.
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Old 9th November 2017, 01:24 AM   #3
dukmang is offline dukmang  United States
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So far no joy. The pics on ampguts of any of the TRA series aren't clear enough to make out any of the values. If I wanted to know what the amp looked like from five feet away that would have been five bucks well spent.

It does look like the TRA800.2 and the TRA500.2 both have similar board layout. Does anybody have any info about either of these amps?
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Old 9th November 2017, 02:30 AM   #4
Perry Babin is offline Perry Babin  United States
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Have you tried the german amp guts site?

Keep emailing them until they send it or tell you it's not available.
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Old 9th November 2017, 03:54 AM   #5
dukmang is offline dukmang  United States
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Nothing that looks close on the German site.

I can't help to wonder why this is proving so difficult. There seems to be a lot of other Soundstream amps with readily available info. Production numbers low? Tough amp with few repairs? Crap amp not worth fixing? Super secret Soundstream technology?

When repairing the power supply on this amp I traced the circuits and drew out the schematic. It was tedious. I'm really not looking forward to it but it looks like I'm going to have to sketch out everything around U3 and try to infer its function and an appropriate value for R8. Presumably its a low to moderate value to dissipate enough heat to liberate itself from the board without leaving a burn behind.
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Old 9th November 2017, 09:56 AM   #6
Perry Babin is offline Perry Babin  United States
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email me
babin_perry@yahoo.com
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Old 10th November 2017, 01:50 AM   #7
dukmang is offline dukmang  United States
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With Perry's help it was determined that U3 is used for the bias control and R8's value needs to match R10. 4.7K in this particular amp.
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Old 26th November 2017, 04:56 AM   #8
dukmang is offline dukmang  United States
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I finally had time and parts to finish up working on this amp. I've now got +-55V on the rails and +-14.5 on the op amps thanks to a complete rebuild of the power supply.

When I had the amp apart and inspecting it for damage something curious jumped out at me. All of the NPN output transistors had a similar looking burn mark on the bottom of the center lead near the body of the transistor. Unable to find a matching burn mark anywhere on the board or heat sink I chalked it up to a manufacturing artifact. The transistors all tested good so I didn't think much more about it.... until I powered it up all screwed down in the heat sink. SNAP! SNAP! two loud arcs came from the vicinity of the outboard output transistors. I shut it down quick and pulled the clamp to look for the problem. Nothing obvious. I screwed it all back together and connected the RCAs to a deck, a speaker on the outputs, and put a signal to it. Plays fine on both channels and bridged. Fiddling with the deck controls I got a 3rd SNAP which also hit the speaker pretty hard. Otherwise it sounds great and nothing is heating up.

Needless to say I need to get to the bottom of this arcing from the center lead of the NPN transistors. FWIW, this amp has 6 NPN and 6 PNP (TIP 35 and 36) spaced out as 3 NPN, 6 PNP, and then 3 NPN. Despite being separated by 6 transistors all of the NPN have the very similar mark on the center leads. Both outer leads on all of the output transistors (and several other components on the sink) have insulating sheaths. I suspect that this arcing is what originally destroyed the power supply in this amp. There doesn't seem to be any ill effects from the couple of arcs I witnessed but if all 6 are arcing I'm sure my new power supply wont last long.

Can anybody shed light on this problem? What should I check? Any tests I can do? I don't feel like I can reposition the leads enough to make a difference.
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Old 26th November 2017, 10:03 AM   #9
Perry Babin is offline Perry Babin  United States
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Although it would be unlikely for the center lead, it is possible for the leads to break just inside the casing. That could account for the problem your having.
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Old 26th November 2017, 07:12 PM   #10
dukmang is offline dukmang  United States
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I'll double check that but to be clear the arc was to the chassis not from the lead to the body of the transistor. A bright blue flash accompanied the arcing similar to an automotive ignition coil. What I referred to as a burn wasn't the traditional burned up components look. The spot I'm struggling to describe looked like a small dot of heavily oxidized solder in about the same spot on all of the NPN center leads. Wish I had taken a picture now.
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