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Sunn Solid state amp not repairable?

#21
agedhorse said:
Any qualified service tech should be able to fix that amp. There's nothing unusual or remarkable about it.
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Passinwind said:
I fixed plenty of those amps back when they were still in production. Very easy to work on, for the most part.
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johnk_10 said:
i've repaired a lot of Sunn Beta and Coliseum amps over the years and IME, they're pretty easy to fix.
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I didn't get a chance to speak to the second tech directly, but he sent me a message about why he can't fix it:

"These amps are very badly made to begin with and are very prone to different issues, and very difficult to troubleshoot as well. Sorry we couldn't be of more help with this."

I know that these amps weren't considered high-end or boutique back when they were made, but I'm a bit surprised by this statement, especially after reading your comments in this thread.

I found a music store in a neighboring city that has a tech who can fix solid state amps, but he isn't available until August :meh:.
 
#24
TFM94 said:
I didn't get a chance to speak to the second tech directly, but he sent me a message about why he can't fix it:

"These amps are very badly made to begin with and are very prone to different issues, and very difficult to troubleshoot as well. Sorry we couldn't be of more help with this."

I know that these amps weren't considered high-end or boutique back when they were made, but I'm a bit surprised by this statement, especially after reading your comments in this thread.

I found a music store in a neighboring city that has a tech who can fix solid state amps, but he isn't available until August :meh:.
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I'll reach out to a good tech I know in Finland, who I initially met a few years ago on Basschat. Perhaps he can suggest someone who can help you out a little sooner than that.

Sunn as a company had a lot of ups and downs back when that amp was in production. I was a warranty service provider and a lot of the work I took in was related to their PA equipment, especially the power amps, which the outfit I worked for rented to institutions like schools and churches where they may not have always had pro operators. AFAIK they stayed fixed pretty well, I don't remember getting many callbacks.
 
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#25
Passinwind said:
I'll reach out to a good tech I know in Finland, who I initially met a few years ago on Basschat. Perhaps he can suggest someone who can help you out a little sooner than that.
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Your help is most appreciated, thank you very much! Please let me know how it turns out.

I got the amp back today and ran a few more tests: Here's what I observed:
1. the power indicator lamp turns on
2. Both channel input LEDs turn on when I plug into the respective jack.
3. When running either of the preamp channels in the fx return of another amp, there is a loud buzzing sound, but no sound from the bass itself. However, when I turn the treble control (which is a bit scratchy), I can hear that scratching noise through the speaker.

I'm not entirely sure what all of this indicates, perhaps there are multiple issues.
 
#30
paskisti said:
Has OP tried to ask F-Musiikki in Helsinki who is their approved repair shop? They used to be importer for Fender, ans supposed to be still. If they have official repair shop they could get service manual from Agedhorse.
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Thanks for the tip! I haven't tried F-Musiikki yet. I just checked out their website and they have an electronics repair shop in Vantaa, which isn't too far away. I'll give them a call tomorrow.
 
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#33
I now found a very reputable repair shop in Kuopio. I called and it turns out they have a tech who can work with solid state amps. I'll have to ship it to them (they are 5h away), but this was the first tech I talked to who was actually knowledgeable and helpful. He mentioned that of course there is always a small chance that they can't repair it, but it seems promising and I'll give it a shot.

agedhorse said:
If you find a Fender authorized service shop that is willing to work on it, I can share the service manual with that shop. The Sunn brand is still owned by Fender so I need to follow the proper procedure even though the brand is not current.
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While they frequently repair Fender amps, also under warranty, they're not an authorized Fender repair shop. The tech also confirmed my earlier suspicion: There are none in Finland.

Zooberwerx said:
I really hope you get this fixed. My first good amp was a Sunn Beta Bass w/ matching 2x15 cab. I recall the paper warranty sticker read "1980". The pre section is the "keeper", so to speak.
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I'm trying my best to get it fixed! Mine doesn't have the warranty sticker anymore, is there any other way to determine the production year?
 
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#34
TFM94 said:
I now found a very reputable repair shop in Kuopio. I called and it turns out they have a tech who can work with solid state amps. I'll have to ship it to them (they are 5h away), but this was the first tech I talked to who was actually knowledgeable and helpful. He mentioned that of course there is always a small chance that they can't repair it, but it seems promising and I'll give it a shot.


While they frequently repair Fender amps, also under warranty, they're not an authorized Fender repair shop. The tech also confirmed my earlier suspicion: There are none in Finland.


I'm trying my best to get it fixed! Mine doesn't have the warranty sticker anymore, is there any other way to determine the production year?
Click to expand...
This is good example why it does not matter how high quality and repairable modern amps are. Spare part price and lack of good service workshops makes things complicated. Most workshops replace just PCBs and when out of warranty, unit will be scrap due to high spare part costs. Markbass amps are good example.
 
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#35
TFM94 said:
I now found a very reputable repair shop in Kuopio. I called and it turns out they have a tech who can work with solid state amps. I'll have to ship it to them (they are 5h away), but this was the first tech I talked to who was actually knowledgeable and helpful. He mentioned that of course there is always a small chance that they can't repair it, but it seems promising and I'll give it a shot.


While they frequently repair Fender amps, also under warranty, they're not an authorized Fender repair shop. The tech also confirmed my earlier suspicion: There are none in Finland.


I'm trying my best to get it fixed! Mine doesn't have the warranty sticker anymore, is there any other way to determine the production year?
Click to expand...

I'm guessing circa '79. There was an entire Beta series with a corresponding Chris Squire "cut the crap" endorsement. I was 21 and bought the hype…turning 65 in 2 weeks so do the math. Paid $500 for the rig and that included the switching pedal. Another builder cloned the pre section in a dedicated pedal but I believe that went the way of the dodo bird. Still curious as to whether the "pre out" works. You could always slave a cast-off lead sled power amp.

Riis
 
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#36
TFM94 said:
I now found a very reputable repair shop in Kuopio. I called and it turns out they have a tech who can work with solid state amps. I'll have to ship it to them (they are 5h away), but this was the first tech I talked to who was actually knowledgeable and helpful. He mentioned that of course there is always a small chance that they can't repair it, but it seems promising and I'll give it a shot.


While they frequently repair Fender amps, also under warranty, they're not an authorized Fender repair shop. The tech also confirmed my earlier suspicion: There are none in Finland.


I'm trying my best to get it fixed! Mine doesn't have the warranty sticker anymore, is there any other way to determine the production year?
Click to expand...
PM me the service shop's information, I will see what I can do to help them.
 
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#38
Zooberwerx said:
Another builder cloned the pre section in a dedicated pedal but I believe that went the way of the dodo bird.
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There were/are a handful: Correct Sound made some but seem to be dead; Shift Line made what looks like it would have been an awesome Beta pedal, but it's discontinued; and Hilbish has both rack preamps and amp-amps, but they seem crazy expensive.
This is a design I would expect from a company like Master Effects, but nothing thus far, as far as I know of.
 
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#39
Fender used to have the service manual on their website for anyone to download.
I think there is only 1 IC in the channel switching circuit that is not made anymore, but there are workarounds for that problem with other components. All other components are available to buy in shops.
There are 2 variants of the schematic, the tone stage is slightly different between the 2 versions.
The pre-amp version that is in the larger service manual is the one that many people make into pedals, there is only 4 components different between the bass and the lead amps per channel.
You can turn a lead into a Bass by changing 4 capacitors per channel, 8 caps all together, but bass does not come with the reverb circuit added.

The power amp is the same in the alpha amp but the schematic is easier to read in the Alpha schematic so I threw that in as well.
Cheers
Michael
 

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#40
Tassieviking said:
Fender used to have the service manual on their website for anyone to download.
I think there is only 1 IC in the channel switching circuit that is not made anymore, but there are workarounds for that problem with other components. All other components are available to buy in shops.
There are 2 variants of the schematic, the tone stage is slightly different between the 2 versions.
The pre-amp version that is in the larger service manual is the one that many people make into pedals, there is only 4 components different between the bass and the lead amps per channel.
You can turn a lead into a Bass by changing 4 capacitors per channel, 8 caps all together, but bass does not come with the reverb circuit added.

The power amp is the same in the alpha amp but the schematic is easier to read in the Alpha schematic so I threw that in as well.
Cheers
Michael
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Thank you very much, this is very useful. Is this the same service manual/schematics that @agedhorse and @Fishheadjoe were talking about?
 

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