KA-7300 relay driver transistor

Hello everyone. I recently bought a Kenwood KA-7300 integrated amplifer. In the first few days of use I noticed that the relay would take a while to click. First time I turned it on it took about 30 seconds or so. Then the next time a little longer and then the next time almost 20 minutes. Then the next time I fired it up the relay would not click on no matter how long I left it on for. But the times it did click on the amp worked perfectly.

So I did some research about this amp and came across a thread over on Audio Asylum with a guy that seemed to have the exact same problem that I'm having. Here is the thread:
http://www.audioasylum.com/forums/vintage/messages/18/184035.html

The response to the question in that thread was:

posted by AlbuquerqueAudio on August 5, 2007 at 18:00:25
For some reason, the relay driver transistors in the KA-7100 and KA-7300 are almost always dead or dying. These transistors operate in saturated mode for their whole lives, and for some reason Vcesat rises as the years go by. I often see these models where you can turn them on, and 30 minutes later the relay will click.

Nothing special is needed for this driver transistor...it needs a Vce of 50V or better, and Ic of 200mA or better. I keep a pile of Zetex ZTX1056A's to use as relay drivers...that'll take care of the issue for the life of the amp.

Dk7 should be replaced (1N4004 is fine) as they can go leaky and steal current from the relay coil. Should also replace Ck7, Ck8 (non-polar), and Ck9.

Offset is a tad high, but that's not the fault of the module. Qe1 and Qe2 have lost gain over the years, and no longer are a close match, so base currents go up and offset looks bad. I've been using matched pairs of Zetex ZTX795B PNP's to replace input pair transistors with excellent success (but the lead layout is CBE instead of the stock 2SA750's BCE arrengement, so care must be taken in mounting). On a few 7300 that the owner wanted totally tweaked, I built a few opamp DC servo's to compensate. Kinda cool to see offset hang tough at 0.1mV.

Best 'O luck...you'll have that Kenwood singing in no time.

Click to expand...

So my questions are:

Is this most likely the problem with the amp?

Do both of these transistors in this picture need to be replaced or just the smaller one? http://img3.imageshack.us/img3/2282/circlespj.jpg

Is it absolutely necessary to replace Dk7, Ck7, Ck8, and Ck9?

And lastly and most importantly, how and where can I go about getting these parts?

Here is a view of the location on the schematic: http://i128.photobucket.com/albums/p173/stavenmist/aaaa.jpg

I'm pretty confident I can replace them myself. I've soldered many times, and I've done a little work with newer radios replacing parts. I would really appreciate any help at all. Thanks everyone.

Steve

You're quote was written by me...who the hell is AlbuquerqueAudio?

Anyway, if you're going in to fix it, why are you concerned about having to replace a few extra parts? The idea is to get in there, fix it, and be done.

Yes, the most likely problem is the relay driver transistor, Qk2. I'd replace ALL the electrolytic caps on the board, along with Dk7, Qk2, and the relay.

All the parts are available at Digikey. The Zetex ZTX1056A is NLA, so use the Panasonic 2SC1567S.

Qk2 -> Panasonic TO-126 - 2SC15670S-ND
Ck5,6 -> 470µf 25V Panasonic FM - P12388-ND
Ck8 -> 100µf 16V Panasonic SU Bipolar - P1167-ND
Ck7 -> 10µf 50V Panasonic FC - P10316-ND
Ck9 -> 100µf 25V Panasonic FM - P12924-ND
Dk7 -> UF4004 - MCC Diodes - UF4004-TPMSCT-ND
Relay -> Omron MY4-02-DC24 - Z2634-ND

All Digikey part numbers. Check that the cap values have not changed, as there are sometimes production changes on shipped products...the values above are based on the schematic values.

Thank you EchoWars. Man you've been helping me with everything

I have no idea who AlbuquerqueAudio is lol.

I assume that the Panasonic 2SC1567S is the same as Qk2 -> Panasonic TO-126 - 2SC15670S-ND, correct?

The smaller transistor circled in the picture, that one does not need to be replaced? And "Dk7 -> UF4004 - MCC Diodes - UF4004-TPMSCT-ND" is on backorder. Is there an alternative or should I wait until they get them in. It says March 16th.

Thanks again.

Steve

Stavenmist said:

Thank you EchoWars. Man you've been helping me with everything

I have no idea who AlbuquerqueAudio is lol.

I assume that the Panasonic 2SC1567S is the same as Qk2 -> Panasonic TO-126 - 2SC15670S-ND, correct?

The smaller transistor circled in the picture, that one does not need to be replaced? And "Dk7 -> UF4004 - MCC Diodes - UF4004-TPMSCT-ND" is on backorder. Is there an alternative or should I wait until they get them in. It says March 16th.

Thanks again.

Steve

Click to expand...

You should have no trouble using an On Semiconductor MUR160.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MUR160GOS-ND

Stavenmist said:

Thank you EchoWars. Man you've been helping me with everything

I have no idea who AlbuquerqueAudio is lol.

I assume that the Panasonic 2SC1567S is the same as Qk2 -> Panasonic TO-126 - 2SC15670S-ND, correct?

Click to expand...

Not the same, as they are obviously different numbers. But a fine replacement, as are all the parts I recommended.

The smaller transistor circled in the picture, that one does not need to be replaced? And "Dk7 -> UF4004 - MCC Diodes - UF4004-TPMSCT-ND" is on backorder. Is there an alternative or should I wait until they get them in. It says March 16th.

Click to expand...

The other small transistor is probably fine. As far as the diode, Digikey shows a stock of almost 10,000 of them, so I don't know where you're getting that they're backordered.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=UF4004-TPMSCT-ND

Oppps I copy and pasted the wrong part. The 100µf 25V Panasonic FM - P12924-ND is on backorder until March 16th. Is there an alternative to that part?

I was just confused when you said, "The Zetex ZTX1056A is NLA, so use the Panasonic 2SC1567S." But I assumed that is the Qk2 -> Panasonic TO-126 - 2SC15670S-ND you are referring to.

C'mon EW, that's not the first time you've been plagierized.

Stavenmist said:

Oppps I copy and pasted the wrong part. The 100µf 25V Panasonic FM - P12924-ND is on backorder until March 16th. Is there an alternative to that part?

Click to expand...

Sure. Use the Nichicon 100µf 25V PW, #493-1820-ND.

kcollins4 said:

C'mon EW, that's not the first time you've been plagierized.

Click to expand...

Someone probably did a botched job of quoting me. But I got other things to be worried about.

Well, I replaced all the parts recommended in echowars' order list above (pay attention: CK5, 6 --> that's TWO 470µf 25V capacitors! I missed that but fortunately I ordered extras).

My recently acquired 2nd KA-7300 which was taking 6 minutes, 20 minutes, sometimes not at all to power up -- now powers on in about 1-2 seconds!

I agree with sake as he mentioned in another thread, the relay is the toughest.

I first removed Ck9, Qk2, Dk7 to get a clear shot at the relay.
I tried to desolder the first two posts of the relay and prying between the circuit board and relay with a jeweler's screw driver, then the next row of four. As I got more space, I used a slightly larger small screw driver as a wedge. A lot of patience and jiggling with my fingers on the relay, it finally came free. Note the last row is not soldered at all.

I kept track of all the screws using a plastic ice cube tray. Empty egg shell cartons will work. Recommended to label where they go and take pictures as necessary. Easy to lose track and misalign the frame overlaps on this one. For easier access, you need to remove the side panels, remove screws holding the back panel on the side brace and screws on the chassis bottom. And 2 screws on the brace on the chassis that is by the Input selector shaft. The knurled knob just pulls out of the selector knob shaft.

I also drew a picture map of where each part belongs. Marked with specs µf/Volts. As I extracted the part, I just placed them on the map.

I used an x-acto knife on the glue of the first capacitor but after pulling on it, I found I didn't need it. The glue pulls apart like taffy.

When installing the new relay, be careful when inserting that the holes are clean so you don't tear the traces when poking through. Even so, I managed to heat and flatten the trace back down so it seemed ok.

I also resoldered some of the dirty looking solder points. One of the zener diodes looked slightly burnt, so I wasn't sure if that was one of the problems or was going to be a future problem, but since everything works after installation of all the new parts, I'm not too concerned.

I wasn't sure how the transistor Qk2 was oriented. The pdF didn't really help a newb like me. When I removed it, I saw in the light, that the front had writing that matched the replacement transistor. So I just installed it as the original.

The only other thing is the new black cylindrical replacement Dk7 diode had a bar on one end unlike the white unmarked oval original. I did a search on the web and just followed the symbol on the board -->| means the bar is oriented at the end of the arrow. Not sure if it would have made a difference but as I said, it works.

Good job!

Pic of the rear panel.

It looks intimidating with all the wires, but if you remove the screws securing the rear panel you should be able to pull it out to give you more working space to remove the relay.

Ok I know this is old but I just spent some coin on a very very clean 7300. Plugged it in and I get nothing. It has very little dc offset 6mv or so and playing a 1khz test tone provides a nice clean sine wave out on pin 6 all the way to pin 19 on the relay board. Same thing for the other channel. So I follow this post order the parts took me about an hour to install. Relay came out nicely with some wick and a suction gun.

But still no relay action wth is going on here been dying to hear this bad boy on some Klipsch kg4's

Nvm checked voltages and 50v feed was not making it through rk7. Replaced with two 1/4 watt 100k in parallel since that's all I had lying around.

This amp sounds very good. In fact I don't think the klipsch have ever sounded this good with so much depth and great bass. Imaging has never sounded this good either.

Hopefully get around to recapping the pre amp section but for now I'm going to leave it alone.

Hi Echowars,
I have a 7300 that is not sending any power to the speakers. In coming across your post I tried to add those parts from Digikey and it appears that the Qk2 -> Panasonic TO-126 - 2SC15670S-ND transistor is no longer stocked. Do you have any idea as to a suitable alternative by chance?

I saw in another thread that you mentioned the KSC2690AY will be a suitable replacement. Digikey seems to have two: KSC2690AYSFS-ND & KSC2690AYSTU-ND with the only difference being the DC current gain (SFS = 35 @ 5mA, 5V and STU =160 @ 300mA, 5V). Any recommendation here?

Many thanks!
Jon

EchoWars said:

You're quote was written by me...who the hell is AlbuquerqueAudio?

Anyway, if you're going in to fix it, why are you concerned about having to replace a few extra parts? The idea is to get in there, fix it, and be done.

Yes, the most likely problem is the relay driver transistor, Qk2. I'd replace ALL the electrolytic caps on the board, along with Dk7, Qk2, and the relay.

All the parts are available at Digikey. The Zetex ZTX1056A is NLA, so use the Panasonic 2SC1567S.

Qk2 -> Panasonic TO-126 - 2SC15670S-ND
Ck5,6 -> 470µf 25V Panasonic FM - P12388-ND
Ck8 -> 100µf 16V Panasonic SU Bipolar - P1167-ND
Ck7 -> 10µf 50V Panasonic FC - P10316-ND
Ck9 -> 100µf 25V Panasonic FM - P12924-ND
Dk7 -> UF4004 - MCC Diodes - UF4004-TPMSCT-ND
Relay -> Omron MY4-02-DC24 - Z2634-ND

All Digikey part numbers. Check that the cap values have not changed, as there are sometimes production changes on shipped products...the values above are based on the schematic values.

Click to expand...

It's the same transistor. The "TU" designates the packaging and stands for "tube" (whatever that means). https://www.mouser.com/Search/CompareProducts.aspx

The KSC2690 is a good sub here.

Before you swap the relay driver transistor measure pin #6 (has a wire attached, should be marked OUT)on the bottom of each amp board for DC voltage. You're looking to see milivolts here, 0 being ideal but unrealisitic. You'll likely see less than 100mv, more likely 20-50mv. Large amounts of DC here indicates a problem on the amp board or a toasted module. Large amounts of DC will prevent the relay from closing, as designed.

If that checks out do as EchoWars says and replace the relay driver as well as the electrolytic capacitors, the diodes and the relay. The power supply board on these gets wicked hot and failed caps are common.