700M made a sizzle noise....POP....won't power up.

I did "live chat" with a Digikey customer service rep via their website.
Having all of my info at the ready helped, such as order number, customer number, etc.
In the live chat, I sent links to the listings on both vendors websites, pointing out the manufacturer's part number for the product, to show that they were indeed the same product. Requested the price match, and it was approved. She guided me through the process of adding the adjusted price to my order. In this case it was pretty simple.
 
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Massive variation in cost and type (Silicon/non; conductive/non) for thermal grease, isn't there? I'm inexperienced with this stuff. I need to grease the mica washers attached to the TO3 outputs. What's the recommendation here? I just need a small amount and would like to spend as little as possible. Arctic Silver 5?
 
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The silicone oil tends to separate from the zinc oxide while sitting, and if you buy a jar of the stuff it may need a good stir before use.
 
If Digikey was out of stock with 2SC4793's for awhile, and I wanted to substitute another transistor for Q9 and Q10 on the Driver Board, does anyone have a suggestion? I want to place my order but this item is backordered so it's holding me back.
 
Latest rebuild of a 700M, parts used:

Qe1, Qe2 - 2SA970BL
Qe3, Qe4 - KSC2690AY
Qe5, Qe8 - ZTX795A
Qe6, Qe7 - ZTX694B
Qe9 - 2SC3902T
Qe10 - 2SA1507T
Qe11 - MJF15030G
Qe12 - MJF15031G
 
Latest rebuild of a 700M, parts used:

Qe1, Qe2 - 2SA970BL
Qe3, Qe4 - KSC2690AY
Qe5, Qe8 - ZTX795A
Qe6, Qe7 - ZTX694B
Qe9 - 2SC3902T
Qe10 - 2SA1507T
Qe11 - MJF15030G
Qe12 - MJF15031G

Once again, you're of great help.

Once I get underway with the recap, I will try to add pics of the project to this thread. Just so that it might be of use to others. We all like photos, right?
 
Latest rebuild of a 700M, parts used:

Qe1, Qe2 - 2SA970BL
Qe3, Qe4 - KSC2690AY
Qe5, Qe8 - ZTX795A
Qe6, Qe7 - ZTX694B
Qe9 - 2SC3902T
Qe10 - 2SA1507T
Qe11 - MJF15030G
Qe12 - MJF15031G

Ok, A small point of confusion with the list. My Driver board Q9 and Q11 are the same, both are NEC D381, stock, I think. Whereas your list above contains two different transistors, with different values. Why not replace two D381's with two substitutes, but keep them the same, not one for Q9 and a different for Q11?

Same goes for my Q10 and Q12- they are both NEC B536 native to the board, whereas you have non-similar subs in your list.

Is this an old board vs. new board question? Mine's a new board, I think.

Thanks.
 
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Yes, we are referring to the new style board, just like yours.

Kenwood used TO-220 devices (2SB536 & 2SD381) in the pre-driver stage. Not sure why. Note that although Q11 and Q12 are heatsinked, Q9 and Q10 are not. Reason being that, two stages away from the output devices, the collector currents are much lower, and thus power dissipation as well. A TO-220 in this position is not really necessary, and you can get much better current gain with a good quality TO-126 that can handle the voltage and current, and be capable of dissipating a watt or so as well.

Might note that it's pretty common for the threads on the soft aluminum heatsinks for Q11 and Q12 to be pretty much trashed. I get a nut to put on the back side of the heatsink with some Loctite small-screw threadlocker (3mm, 0.5mm pitch, or just trash the thread completely and use a SAE #4 machine screw and nut).
 
Thanks for clarifying.

Funny, Digikey doesn't even seem to stock 2SA970BL. It's not that they are out of stock or backordered They don't carry it; well, no listing anyway...seems odd to me.

I may just stick with the ZTX795A's that you suggested ordering a couple dozen of, for close matching.
 
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Just to be totally certain, if I have a new style driver board, x07 1310 00, I should install the Q5 transistor such that the Collector and Emitter are reversed, relative to what is stated on the circuit board, correct?
 
Here's a fairly important detail. I just measured the HFE gains of my ZTX795A's for Q1 and Q2 on each driver board. In descending order, below, are the values. All those above 500, I didn't consider for selection, because the spread of values was too large (515 to 557). So, in terms of keeping similar gains (within 5%) but also high gains, I am thinking of picking 499 and 496 as a pair, and 492 and 489 as a pair. Will this be ok? Also, is it a problem that the first pair (499/496) on one board, would have a slightly higher average gain overall than the second pair (492/489) on the other board?

557
539
531
515
499
496
492
489
488
486
483
472
471
469
468
461
452
450
446
441
436
434
427
422
 
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Once the gains get high enough, the disparity in the gain from one to the other starts to become less and less important. I'd take the first four and call it good.

As far as Qe5's orientation, refer to this post. The only way for the foldback circuit to work is if Qe5's collector connects to Qe7's emitter (and the output line). Qe5's emitter must connect to the base of Qe9. Every 'new' style board I have ever seen has this wrong. Since your board is not here for me to look at, I cannot say with 100% certainty that yours is the same way. Study the orientation on your board and figure it out.
 
Once the gains get high enough, the disparity in the gain from one to the other starts to become less and less important. I'd take the first four and call it good.

As far as Qe5's orientation, refer to this post. The only way for the foldback circuit to work is if Qe5's collector connects to Qe7's emitter (and the output line). Qe5's emitter must connect to the base of Qe9. Every 'new' style board I have ever seen has this wrong. Since your board is not here for me to look at, I cannot say with 100% certainty that yours is the same way. Study the orientation on your board and figure it out.

Thanks for the tips on the gains, Echowars. I'll go with the 500+'s for Q1 and Q2.

As for the Q5 and Q9 question, happy to say I did install it correctly on my board. Attached are a couple of pics for anyone interested. Hope they might help someone in future. Note, my board is apparently the "new style" x07-1310-00. The Q5 I used is this:

http://www.digikey.ca/product-detail/en/0/ZTX795A-ND
 

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I've mounted the aluminum soft start resistor directly to the chassis, on the little steel mount thing that the old ceramic SS resistor was formerly attached. Aluminum is conductive. Is this a problem? Should I assume that the new resistor is shielded on the inside?
 
I am very close to powering up my 700M after an almost-complete recap and overhaul on the electrolytics, v/i transistors, all 12 output transistors, soft start resistor, bias trimpots, speaker relays, etc.

What I didn't replace: SS relay, zener diodes, and two oil filled caps (though I should), and those two jumbo filter caps ($$).

I've built a dim bulb tester, hopefully that will prevent any disasters upon firing it up.

NOTE: I am uncertain about how to adjust the trimpots on the driver boards. What bias setting they should be at. What the method of adjustment is. However, I just adjusted it so that it was super low, using a DMM to dial it down to almost no ohms. Bad idea? Just uncertain about this. Will look at service manual.
 
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Ok, so i powered up using my Dim Bulb Tester. I'm totally new to the idea of a DBT, but I followed the instructions carefully and made one with a 100w bulb. Here's the video of the DBT test:

Here's the video:
https://www.youtube.com/watch?v=rIu5qRUTVy8&feature=youtu.be

My attempt was not the most promising: after turning it on, the bulb illuminates fully, then gently fades. First relay >click< (SS relay?), nothing happens, bulb just continues to fade. Second relay >click< (speaker relays?), the bulb goes full bright. I have a short, or some other problem here, right? Can any AK geniuses help me with the logic of the problem?
 
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