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Just bought a Technics SU 8080 and it burnt - help

muzah

muzah

New Member
warning - I don't speak english quite good, I hope you'll understand my problem.

:) bonjour tout le monde !

As you can see, I'm not american and don't practice english every day, so I hope you'll understand the following words.

I recently bought an amp Technics SU-8080 for few bucks. Back home, I open it and plug. But it doesn't play. A resistor burnt near the big germanium transistors. I changed it but it burnt too.

Without the resistor, another one burnt on the card plugged into the main board. Here is a picture of the two "victims" :



Could you help me to find the problem or anyone has the service manual of this amp ? I'm not very good in electronic operation, but it's time to take some lesson from you :)

Thank you !

Regards from France :)
 
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let me be the first to say:
Welcome to AK!
I had problems with my receiver, and don't worry, the people here will take care of you
 
:beerchug: Congratulation ! You're the first :D

Thank you for the nice reception :)
I'm sure this forum is full of qualified and impassioned people :yes:
(I hope too, otherwise I'm screwed...)
 
You have a shorted transistor. Most likely it is the one associated with that resistor. One or both of those germanium transistors are shorted.
 
I don't see any wire or something that could shorted the transistors.
A transistor can be shorted inside ?
Then, there are two transistors on the same way, why could I verify witch one is "dead" ?
 
I just take continuity tester and put on the two pins of each germanium transistor.

On the "good" way, nothing append, on the "bad" way, the tester "biiip" for each two transistors. Could it be a clue for one of the transistors on the bad could be shorted ?
 
Bonjour Muzah, et bienvenue chez AK,

I have a schematic for the SU-8077 and there may be some similarities between the two circuits. First, I doubt there is any germanium transistors in this amplifier. And there must be three pins on transistors...

Can you tell us what is the part number for the resistor near the TO220 transistors. What are the part number printed on each of the TO220 transistors? I will see if the 8077 schematic can be helpful.
 
Hello ecluser :)

I'm not sure 8080 and 8077 are similar. First off all, the 4 power transistors are made of germanium :





The fact is they look like, isn't it ?

I just take a close look inside the amp, I don't find any TO220 transistor :/
 
You'll have to remove the transistors to test them, they cannot be reliably tested in-circuit, no way no how.

1. Download the datasheets from the link above
2. Determine which leads are Base, Emitter, and Collector.
3. Using the diode check function of your multimeter, test continuity between Base --> Emitter, Base --> Collector, and Emitter --> Collector.

Base --> Emitter should conduct ONE WAY ONLY with a voltage drop of ~0.7V
Base --> Collector should conduct ONE WAY ONLY with a voltage drop of ~0.7V
Emitter --> Collector should have NO CONDUCTION EITHER WAY.

If any of these conditions fails to be met, the transistor is bad.
 
dspear99ca said:
You'll have to remove the transistors to test them, they cannot be reliably tested in-circuit, no way no how.

1. Download the datasheets from the link above
2. Determine which leads are Base, Emitter, and Collector.
3. Using the diode check function of your multimeter, test continuity between Base --> Emitter, Base --> Collector, and Emitter --> Collector.

Base --> Emitter should conduct ONE WAY ONLY with a voltage drop of ~0.7V
Base --> Collector should conduct ONE WAY ONLY with a voltage drop of ~0.7V
Emitter --> Collector should have NO CONDUCTION EITHER WAY.

If any of these conditions fails to be met, the transistor is bad.
Click to expand...

Thanks for this reply, this is weekend, then I should find a moment to do this :)

Thanks to inductor too !
I haven't any scope by my side, but I can try to find one on loan.

regards :)
 
Great avatar, the bunny instead of Homer Simpson in Munch's 'The Shriek' ('skrik'). (Original may have been from a Peruvian mummy from a museum). link
El+Crit,+E.Munch,+1893.jpg


Traded one of those a few weeks ago. Technics, not the painting! I like anything with dual trannies...

The front black aluminum panel and especially the cast volume knob are heavy and sturdy--not like the BPC.

Weak link was two of the flip switches on the front. Direct/ - DC/. Intermittant behaviour. No amount of D5 would help. When it made the connection, it sounded quite nice. Better than the NAD 7250PE. But my speakers are too inefficient. Great office headphone integrated amp?
 
Does tourne-disque really mean "record player"?

muzah said:
warning - I don't speak english quite good, I hope you'll understand my problem.

:) bonjour tout le monde !

As you can see, I'm not american and don't practice english every day, so I hope you'll understand the following words.
Click to expand...

Welcome!

I thought your English was pretty good!

It may be better than some of our other Akers that only speak English!

Good luck on your repair! :thmbsp:
 
Susurus said:
Weak link was two of the flip switches on the front. Direct/ - DC/. Intermittant behaviour. No amount of D5 would help. When it made the connection, it sounded quite nice. Better than the NAD 7250PE. But my speakers are too inefficient. Great office headphone integrated amp?
Click to expand...

Say, I have that amp! I've got it working perfectly, now, it is a very sweet sounding amplifier, and it has more than enough power to drive my AR94s to quite loud levels.

muzah, here is the service manual for the SU 8080. Get it on paper, then start a repair thread. There are plenty of people here who will help you out.
 
tarior said:
Say, I have that amp! I've got it working perfectly, now, it is a very sweet sounding amplifier,
Click to expand...

Another success! :banana:

and it has more than enough power to drive my AR94s to quite loud levels. [...]
Click to expand...

Not sure if my main room was just too large for it.

And of course your recapped AR-94s are more efficient than most of my krew... (or your little Marantz has more Ooomph than its specs say...)

I'd given the SU-8080 a turn as part of a bi-amping setup, and it drove the highs belly smoothly...when I fidgeted with the switches to get it to play... :boxing:
 
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