New member and new Sunfire Load Variant Stereo Amplifier with issues

[Johnnyhigh5 17]

Hello, I am new to this site and new to Carver gear. I've been buying, selling, collecting, and fixing vintage stereo equipment for about 10 years now. Love this hobby!

 

I purchased a Sunfire Load Variant stereo amplifier in non working condition. I found that a previous owner did the famous tinfoil around the main fuse trick. I have a melted transistor and diode that I am hoping someone can help with the correct part numbers and a schematic or service manual. The amp boards look fine, just issues with the front board.


Q22 - Q23 is a PNP MJE2955T. Maybe Q22 should be a NPN MJE3055T?

D16 - the diode next to it is a 1N4004.

Thanks in advance!

[BobTFM35 2,316]

Welcome to the Carver site!

 

As for schematics and service manuals, what is in the sites database is all that is available at this point in time. The only thing that one can hope for is a confirmation from someone that has the same unit.

 

This is only a hunch.

 

Looking at the schematics that are available might give some clues and maybe support for your one assumption on Q22.

 

Look at the drawing 653-111-000 page 1, in particular Q21 to Q24. You will see that Q23 and Q24 ( MJW3281A NPN) are complimentary to Q21 and Q22 (MJW1302A PNP).

 

I guess this kind of supports your assumption for the Q22 question?

 

Good luck on the repair of the unit.

 

 

[AndrewJohn 9,401]

Welcome, @Johnnyhigh5, glad you found us.

 

The schematics we have are posted in the library.  Sunfire docs are tricky..., they were never released, so we rely on donors that come across them, to share them here for the library. In addition, Sunfire had many in-production revisions, so not all units match the schematics that we do have in our library.

 

After you do a bit more activity here on TCS, you'll be able to post pictures (it's a thing we do here to prevent spam).  Pictures of the board where you are observing damage would be helpful.  I am not a tech, but an enabler..., 

 

On other suggestion is that replacing burned up parts is important, but not as important as finding the underlying reason for these part to be fried.  It may be the fuse/foil - but likely something else that made the previous owner put the foil in there in the first place..., something was causing that fuse to fail.  That is the issue that needs to be diagnosed and corrected as well - as I'm sure you know with your years of experience.   

 

Please post a picture as soon as you can.

[4krow 5,863]

Welcome.

 

 I look forward to hearing more about this amp and especially what will get it back to working order. Too bad that someone was only smart enough to bypass a fuse.

[Rob 4,833]

Welcome to the site. 

[Johnnyhigh5 17]

Thanks to this great site, I was able to find the power supply schematic and confirmed Q22 is a MJE3055t and D16 is a 1N4004.

 

Here is one picture. The rest were too large to post(over 1 MB).

 

Edited September 10, 2024 by Johnnyhigh5

[Johnnyhigh5 17]

[Johnnyhigh5 17]

[jeffs 3,056]

Transistors don't typically show that much physical damage.

 

Looking at the schematic, the best case scenario for you is that C29 shorted, causing excessive current thru the diode and transistor.

I noticed C29 is removed in one pic. If it measures shorted, it's likely the cause of the damage.

 

The resistors in that circuit can get hot. Their proximity to the 1000uF caps can shorten the life of the caps.

 

I would recommend replacing the 1000uF caps in that circuit, and mounting the replacements on the back of the board.  Can alleviate future potential thermal problems with these caps.

[Johnnyhigh5 17]

2 hours ago, jeffs said:

Transistors don't typically show that much physical damage.

 

Looking at the schematic, the best case scenario for you is that C29 shorted, causing excessive current thru the diode and transistor.

I noticed C29 is removed in one pic. If it measures shorted, it's likely the cause of the damage.

 

The resistors in that circuit can get hot. Their proximity to the 1000uF caps can shorten the life of the caps.

 

I would recommend replacing the 1000uF caps in that circuit, and mounting the replacements on the back of the board.  Can alleviate future potential thermal problems with these caps.

 

Hi Jeff, that is a good idea to mount the caps on the back. I didn't mention it before, but the Zener diode D12 was also shorted.

 

I have ordered new diodes, high temp caps, and transistors. Actually, I ordered all new caps minus the main filter caps.

[Rob 4,833]

3 hours ago, jeffs said:

Transistors don't typically show that much physical damage.

I have seen damage very similar in many other Carver amps typically in TFM's. They get very hot and burn boards. But that one looks like it was cooked nicely. 

Edited September 11, 2024 by Rob

[Johnnyhigh5 17]

8 minutes ago, Rob said:

I have seen damage very similar in many other Carver amps typically in TFM's. They get very hot and burn boards. But that one looks like it was cooked nicely. 

 

The results from the previous owner wrapping the main fuse in tin foil. 😕

[Eyexlr8 85]

22 hours ago, Johnnyhigh5 said:

 

Hi Jeff, that is a good idea to mount the caps on the back. I didn't mention it before, but the Zener diode D12 was also shorted.

 

I have ordered new diodes, high temp caps, and transistors. Actually, I ordered all new caps minus the main filter caps.

No , mount the big resistors on the back side not the caps.  
 

[Cring08 197]

Welcome! Good luck on the repair!

[Johnnyhigh5 17]

Update on the Sunfire Load Invariant Stereo amp:

 

I replaced all the caps in the amp minus the main filter caps. I replaced 2) 13v zener diodes, 2) 1N4004 diodes, 1) MJE2955T transistor, and 1) MJE3055T transistor.

 

Now it works and sounds great! Pairs great with the Sunfire tube pre amp. I would take pictures but they are too large to post 🤷

 

P.S. My amp is an early generation with an attached power cord and slightly different and simpler power supply design. No on/off/auto switch on the back either.