Haffler Transnova query.

[bob s]

Hi again folks, back with another question. I have a Haffler Transnova 9305 that has high D.C. Offset on one channel. I haven't tried to connect loudspeakers to it at risk of blowing the amp or speakers. I need to sort this out so any guidance would be extremely appreciated.
Thanks everyone.

Bob S

 

[avionic]

high D.C. Offset on one channe

How high is high ?

 

[bob s]

The right channel is showing 9.15 volts, the left, .01 volts. I haven't even tried to put signal through it or hook up loudspeakers.

 

[Binkman]

combined 9303 and 9505 user man. and schema's. down page from parts list.
https://www.hifiengine.com/manual_library/hafler/series-9303.shtml

 

[mondialfan]

The easy check,,,,, Did you check the DC rail fuses?
Is yours an early or late model? The late models moved from through hole to surface mount components? The early models (the through hole version) had issues with random failures on Q8, 9, 10 & 11 due to overheating. On these models the transistors in question are usually easily identified because the board is darkened around them due to heat. These are MSPA56/06 transistors and they can be replaced with MPSW56/06 models which are the same device in a higher power dissipation (1 Watt) TO-226 package. I would say your problem is probably either these driver transistors or the output mosfets. The output mosfets are going to be expensive to replace as you'll need matched sets for each channel. If you have to replace the output mosfets you can get matched sets from Profusion here SK1058 & SJ162

Let us know what you find.

 

[Binkman]

The late models moved from through hole to surface mount components

I saw that thru hole note in the schematics, too. I was thinking drivers with excess offset as two amps this week came up with drivers and high dc offset and as noted 'heat" very possible. (no heat sinks.)
But a gorilla mover with no idea of "fragile" and drop it one foot? and all the stuff inside will be subject to a 'drop test'. So really close inspection is needed for same and solder joints and even cable connects come loose.
hope it helps
bink​

 

[bob s]

Thanks for alll the information. I do not know if it is old or new version, haven't popped the lid on it yet. Just trying to get some clue on what it might take to get it fixed and how much it might cost. Trying to decide if I want to tinker with it or sell it as is. I am trying to downsize my project pile that seems to be getting larger than I can cope with.
I will take a peek inside and post results.
Thanks so much.

Bob

 

[dshoaf]

Hi Bob,

From us propeller-heads of audio, trying to diagnose and estimate effort to fix something is roughly like standing outside your car, on the phone, and saying it isn't running but with no other information.

I'd suggest you pull the top off, take some pictures of the internals, especially anything that looks or smells like it might not be right. Post the pictures here at AK and let some of the arm-chair bench techs help you step through basic troubleshooting.

To help get you oriented to troubleshooting, here's a good thread here at AK titled: A Troubleshooting Flowchart.

That's a nice amp and you can learn something about it if you'd like with the help of AK'ers. You have to decide if you want to put in the effort and time is all.

Cheers,

David