Kenwood KA-7100 needs help

[EchoWars]

hpsenicka, L channel blown.

Squidward, transistor is in wrong.

 

[Squidward]

hpsenicka, L channel blown.

Squidward, transistor is in wrong.

I'll go see if I can fix my screwup. Is putting a transistor in wrong ever fatal to other parts of the circuit, or the transistor itself?

Thanks again, I'll report back.

 

[hpsenicka]

hpsenicka, L channel blown.

d'ya think? :scratch2:

Obviously it looks like the L channel output transistors are shot and need to be replaced, but it seems to me there must be more to it that that.....

It wouldn't be as simple as installing a new pair of outputs would it? I'd expect that something else is wrong as well, and that I'd likely just blow up the new output transistors as well.

I haven't a clue where to look next... but am game to poke around and attempt a repair, provided someone is willing to spend some time coaching, and putting up with stupid questions along the way.

Another possible limitation is that I don't have access to a o-scope... just a basic DVM and a soldering iron.

 

[Squidward]

At least one happy outcome

I would like to extend a heartfelt thank you to EchoWars in particular, and everyone who makes this forum what it is in general. I'm listening to sweet music through my now working KA-7100. Not only do I now have noe sweet amp that's been saved from the landfill, but I learned something in the process. What could be better?

 

[bully]

Don'cha love it when a plan comes together!
Way to go AK!!
:thmbsp:

 

[hpsenicka]

congrats!

Way to go Squidward... glad to hear you were successful!

 

[SPL db]

Great job Squidward! :thmbsp:

Kudos to the great EW! :ntwrthy:

Scott

 

[twocoaster]

An old thread... thanks to all so far, especially EchoWars

Too funny...

I don't know why, but every single 7100 I've ever worked on needed a new relay driver transistor. Every bloody one...(OK, there might have been one that was OK, but I've worked on a dozen or more of the things and probably 11 of 'em needed a new driver tranny).

The suspect transistor is Qe34, and is at the very front of the horizontally mounted 'motherboard' of the unit, just about dead-center. I believe that the component designations are silkscreened into the board, so you should have no problem locating it. Immediately next to it is a ground terminal with a couple of black wires on it.

The view here is from the conductor (foil) side of the board.

This pic labelled C1213 is the Q34 position piece in my KA-7100... correct one for relay?

If there is about .6 ~ .7V on the base of the transistor, and 25 to 30-something volts on the collector, then the transistor is bad.

Even a cheapie RatShack 2N3904 will work fine for a replacement, but the pinout of these RatShack transistors cannot be taken for granted...you must determine for yourself which lead is base, collector, and emitter.

It seems that with the three pins, this could only be installed correctly, or 180 deg opposite. Am I thinking right on this?

Thanks!

tc

 

[EchoWars]

This pic labelled C1213 is the Q34 position piece in my KA-7100... correct one for relay?

Looks like the one...

It seems that with the three pins, this could only be installed correctly, or 180 deg opposite. Am I thinking right on this?

No...just because you can get three leads into three holes doesn't mean they are in the right place.

The connections on that transistor are (from rear to front): Base, Collector, Emitter. Not all transistors are laid out that way. While most Japanese transistors have the collector as the center lead (and the base sometimes on the left, and sometimes on the right), many European and North American transistors have the base in the center. I frequently use Zetex ZTX1056A transistors (British) for relay drivers, and they have a CBE layout. They just don't get installed as neatly as the original.

 

[twocoaster]

EchoWars, than you very much for taking the time to explain this! I'll run the checks you described earlier in the thread to determine the configuration of the replacement transistor I use (when I get it).

tc

Looks like the one...No...just because you can get three leads into three holes doesn't mean they are in the right place.

The connections on that transistor are (from rear to front): Base, Collector, Emitter. Not all transistors are laid out that way. While most Japanese transistors have the collector as the center lead (and the base sometimes on the left, and sometimes on the right), many European and North American transistors have the base in the center. I frequently use Zetex ZTX1056A transistors for relay drivers, and they have a CBE layout. They just don't get installed as neatly as the original.

 

[rage]

Just wanted to send all of you guys out a thanks for this old thread. I bought a KA-7100 at a swap meet for $30 and was sadly disapointed that it did not work when I brought it home.

Checked the voltages at Q34 transister, tested bad and replaced with the .79 cent radioshack part. Amp fired right up, relay clicked and it sounds great!

Thanks again guys!

 

[Blue Shadow]

Welcome to AK. Nice first post, shows lots of respect for the members (you used the search function) and quality work on your part. I guess you have already done the Deoxit cleaning while you were in there?

 

[Strawman]

What an interesting thread to be revived. I now happen to own Ed's 7100 purchased from last years 'Fest. This year's 'Fest I added a KT-7500 from ZebraBlvd. Very nice mid-fi matching.

 

[jgmacv]

Just wanted to send all of you guys out a thanks for this old thread. I bought a KA-7100 at a swap meet for $30 and was sadly disapointed that it did not work when I brought it home.

Checked the voltages at Q34 transister, tested bad and replaced with the .79 cent radioshack part. Amp fired right up, relay clicked and it sounds great!

Thanks again guys!

Purchased mine yesterday from the local Goodwill. Same symptoms. After reading this post, got the transistor (2N3904), replaced it and presto!!!! Thanks all!