SX-1010 won't Power On...

LWB said:

On 1010 Power Amp Board AWH-032-0, I'm wondering why you replaced diodes D7 & D8, which were each originally a single 1S1885 diode (rating: VRRM 100 Volt, IFSM 66 Amp) with two Fairchild UF4004 (rating: Repetitive peak reverse voltage 400 Volt, Peak one cycle surge forward current 30 Amp) in series. This seems like less protection rather than more in terms of the current capability of the replacements. Am I missing something?

I attach ccheath's illustration of the components from his earlier posting and a pic of my original unmodified board.

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Here's why, when I was working on Maddart's sx-1010, it had stv3's instead of 1s1885 diodes and one was bad.

then this (post 60):

http://www.audiokarma.org/forums/showthread.php?p=1494762#post1494762

explains EVERYTHING.

Correction

My board is labeled AWH-032-A, the manual labels it AWH-032-O. I did notice that an earlier photo posted by ccheath showed a U-shaped component attached to the output heat sink, and my unit doesn't have such. What is the code on your later Power Amp boards? Can't read it on the latest photo.

LWB said:

My board is labeled AWH-032-A, the manual labels it AWH-032-O. I did notice that an earlier photo posted by ccheath showed a U-shaped component attached to the output heat sink, and my unit doesn't have such. What is the code on your later Power Amp boards? Can't read it on the latest photo.

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That component is a thermal compensation diode and is CRITICAL. There are TWO, one for left and one for right.

LWB said:

In my unit, STV-3H (called Varistors in the Service Manual) are in positions D5 and D6, as per the SM, and are little U-shaped dohickies that attach with a single screw to each side of the heat sink beneath the Q9 & Q10 transistors. Your photo appears to show one of these mounted on the right side of the heat sink, but not on the left side. The service manual shows 1S1885 diodes in the D7 and D8 position, as in my unit (my serial # indicates Sept 74 mfr according to Strangelove's scheme). Are we referring to the same components? What are the components in positions D5 and D6 on your board? I wonder if the board traces are any different.

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Yes, we are referring to the same components. It does sound a little confusing when I say STV-3 which I might have meant STV-3H. I actually mean STV-3 (without an "H") which is an axial lead 3 diodes in a single package which is located on D7 and D8 position. Same position as your 1S1885. On my amp the STV-3H (U shaped horseshoe), one is located on the driver heatsink, and the other is located on the output heatsink connected to pins 21 and 22.

Yes, the traces are a little different with some additional traces and some deleted traces and some components were rearranged a little. My stereo is made in Oct 1975.

And, I wonder if I should make some changes? On the one hand, I know the former owner of this unit liked 'volume', and it hasn't failed yet. On the other, I'm interested in making sure it doesn't fail...

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Only thing is your receiver does not monitor the heat on the output heatsink but both only on the driver heatsink. If the output heatsink gets real hot while the driver still stay cool, you may get a thermal runaway on the outputs. If it was mine, I probably will do some mod but I wouldn't really sweat it unless Markthefixer or Echowars recommends any mod to make on an older board.

Last question - why 'high speed' diodes? The 1S1885 is a general purpose rectifier.

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I recall Echowars suggest that lower speed diodes wouldn't do as good a job as faster diodes. I can't recall exactly what he said on this part. I had subscribed threads but lost all of them because I forgot to update my email info. (stupid me) Maybe Mark has an answer on this part.

Mark answered before my last posting.

My last pic is of AWH 032-D

LWB, here are a few pictures of the STV-3H diodes on the heatsinks, as Mark mentioned, one for the left and one for the right. I am VERY familiar to them as I busted one then the only remaining hoof of the one on the left heatsink. You will notice it is secured to the heatsink by a round washer. They are not very easy to come by either. Hope the pictures help...

markthefixer said:

Not likely, conductive thermal paste would be something like arctic silver and if you got the stuff I specified, that's non-conductive electrically.

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Yes that's exactly what I'm talking about, non-conductive compound. IF a considerable amount was carried by the transistors INTO the sockets, it would surround the transistor leads inside the sockets and might cause bad connection inside. Would this limit the conductivity between the transistor pins and the inside of the sockets?

D.E.K said:

Yes that's exactly what I'm talking about, non-conductive compound. IF a considerable amount was carried by the transistors INTO the sockets, would it have a negative effect on the conductivity between the transistor pins and the inside of the sockets?

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I got some goop on mine even on the pins that gotten into the sockets when I reinstalled the original for testing and it didn't cause any problem. Later when I replaced the outputs with brand new ones, I did actually cleaned them out completely. I don't think the compound is causing contact problem from the symptoms you're describing.

That's a relief, thanks a lot.

I still think your problem may be the regulator board but I'll let Mark lead you there. From what I read, you are still on the protection board project. Your patience has been fantastic for quite awhile.:thmbsp:

Hey EW, received the STV-3H safe and sound. Thank you very much :thmbsp:

I dabbed a spot of epoxy on the body where the leads exit to protect them...hopefully that one will prove a little more durable.

The dot on the body is the cathode. Needless to say, installing it with the leads reversed is a bad thing.

Will keep in mind "the dot" I received the desoldering braid today and practiced a bit. It works good and there has been some burnage on the little board I have been working on but nothing major, better than I expected. No peeling off any traces or anything like that. This can actually work. The components from Mouser is en route.

What wattage soldering iron are you using? I use a fixed 40 watt most of the time. It's hot enough to get in and get out without having to leave it on the joint so long that you cook everything around it. It's too hot for small stuff, but works for me anyway on these boards. The pros use variable temperature units that they can adjust for whatever they are doing, but they are expensive.

The one I'm using is 30 watts so it shouldn't be too bad. Though I think the solder I have might be a tad too thick. It's 0.62''

Over 1/2 an inch? That's some serious solder.

Yeah, one touch of the tip and a big BLOB drops. I will get a smaller one today.

EchoWars said:

Over 1/2 an inch? That's some serious solder.

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:lmao: That's obviously a typo. 0.062 is what I meant. I got some 0.032 today. Looks more like it.

I am going to solder the STV-3H today. Wish me luck.

I soldered the STV-3H diode EW gave me and insulated the wires the best way I can. It looks like sh!Q@* but it's strong and stable. I powered up the unit following the installation with DBT and without it after. No fireworks and no relay click. Waiting for the parts to arrive.