Attempting repair on a burned SA3.0X

[Jacampb2]

I'm working on the repair of the oldest of all my Phoenix Gold amps. This one came in a lot of 3 or 4 amps I snagged a few years back. I really had no intention of working on it, but a family friend wanted an amp and this is the only one I am willing to part with at the moment so I'm trying to fix it [emoji1]

It came with a bunch of nte generic parts subbed in the audio section and the power supply would not come up. I gutted the blown channel and got the power supply to come up yesterday. Today I'm trying to repair the board and then rebuild the blown channel with the proper parts...

Cause of the hole burned in the board? As far as I can tell the last tech did it. The output transistors shorted in the heat sink. It looks like the legs were left far too long. Anyhow is been a while since I have done this work, so it might take a while to get it fixed, but I thought I would share the process.

Pics to follow in the next post because I don't want to upload them with tapatalk...

Later,
Jason

Sent from my SM-N910V using Tapatalk

[Jacampb2]

Here are the pics:

Board with burned spot cut out:


Back side:


Taped off:


Filled with epoxy:


I decided to just fill this with epoxy rather than make a patch pcb. The top gold plated trace is in tact and I suspect it will look better with this repair then a patch piece.

More to follow when the epoxy sets.

Later,
Jason

[vwdude]

im watching this, id love to see how this turns out.

[Jacampb2]

Got a little more done after the epoxy cured.

Patch before sanding:


Sanded out:


Holes drilled and foil back in place:


Gotta go. Dinner time.

Later,
Jason

[Jacampb2]

I also fixed a dei 1100d while I was waiting for the epoxy to cure. I'll post up some pics a bit later...

[RayBuck]

Very interesting.

[trickyricky]

Don't forget to replace those leaky caps...the rails caps are also Panasonic caps that leak.

[lukeman269]

Very cool! I wish I had the patience and time to learn how to fix amps. My soldering skills are marginal at best and my understanding of small electrical components lack heavily. I'm glad there are people to pay to figure the stuff out for me!! Lol

[smgreen20]

Jason...... It's been a while, a long while. Glad to see you poking around still. I missing watching some of your work. Like that monster ZPA like amp you were doing, ZPA0.8 or something like that. What ever happened to that? If I recall, you seemed to disappear.


It's good hearing from you again. Loved watching you and Eric D perform magic on some of these amps.

[Eric D]

Nice work on the patch job. I love seeing people keep these rare amps going despite the effort required to do so.

[Jacampb2]

Thanks Eric. Unfortunately, I am really struggling with this one. I got it back together today and the left (unburned) channel is perfectly fine, the right has zero audio output. I found a few passive odds and ends that were bad, but still no audio. I had to use the NTE drivers that the other guy subbed in, I didn't have anything as close as his were. I did put the correct outputs in it and I have checked every transistor in this channel in circuit. When I had anything that looked remotely fishy, I pulled them and ran them through my super cricket. I haven't found any more bad ones. This channel is completely dead, no bias current or anything. I finally had to put it up for the day or I was going to screw something up out of frustration.

I will get it eventually, but apparently, today is not that day

Here are the pics from today. Had to do some kludges where some foil was broken and messed up but it didn't come out to terrible considering the amount of damage there was.





Later,
Jason

[trickyricky]

Hey PM me your addy and I'll send you the pre-drivers or any other hard to find components.

Don't know if you need these.

[Jacampb2]

Tricky, the photos might be just what I needed. I won't be back in the shop for a few days, but I'm thinking that part of the rebuilt channel has npn/pnp predrivers swapped. Any chance you still have the amp out of the sink and could send me some higher resolution pictures? I'll pm you my email address, but if your amp is back together, then don't worry about it. I'll get it via brute force eventually

Thanks,
Jason

[trickyricky]

I gave the amp to my nephew about 2 months ago, and the pics I have are over 3 years old back when cell phones only had 3MP cameras.

I can say though that the amplifier has an exact mirror right down the center (lengthwise), so if a PNP driver/predriver is near the RCA end on the working CH then it will be the same for the non-working ch. Of course verify with the schematics. I'll send you some pics I have but they are only about 3MP resolution so not that clear.


I wouldn't dare use NTE components, just can't even bare the look of them.

[Jacampb2]

The pics you sent were perfect, thank you very much. I'm not going to keep the nte components, but the closest match I had in stock was a pair of to-220 transistors and the device pin outs are backwards from the to-126(?) cased predrivers. I had those in there flipped originally for testing, and only went back to the nte parts to eliminate the possibility that the predrivers were the issue.

I'll keep you all posted, I'm back to work until Monday though. Thanks abrasion for the pics!

Jason

[Nick666]

Hey Jason

I thought mine was in bad condition until I saw yours. Awesome work in attempting to get the amp up and running again.

Nick


Sent from my iPad using Tapatalk

[Jacampb2]

Well, I didn't get anything done on my one day off, turned out my wife invited friends up for labor day... I did get 10 minutes in the attic electronics lab and managed to install this. I also hung a TI finish one on the door, but the picture did not turn out good...



Later,
Jason

[trickyricky]

You should install LED lights....Better lighting and color too. I made the switch and very glad I did.

[Jacampb2]

I have 4' LED fixtures over the bench, they are more than enough light for working. The other lights are not as yellow as they look. In fact, the one in the middle is LED...

[Jacampb2]

I finally got it! Yay!!! Turned out to be a few things. One, there was a trace on the top of the board that was broken, it was tucked under a resistor and the only reason I spotted it was because I replaced the flame proof resistors by the pre-driver, the 100 ohm one was open, the two 10 ohm ones tested good, but looked blackened so I just decided to change them. Really happy I did now!!! The other problem was the two pre-drivers. I have had them in and out a half a dozen times, but today I was checking for broken tracks and I found the traces from the pre-drivers didn't seem to go where they were supposed to. I started looking closer at the silk screen on the board and what was left of the component outlines for the right pre-drivers looked like they were installed backwards. I carefully went though the pictures Rick sent me and sure enough, the pre-drivers were in backwards. I turned them around, patched up the traces and hooked her up and it fired up and worked fine. Yay!!!

After that I went through and sanded out the burn marks on the inside of the sink where the pre-drivers had shorted to the sink. I glued in a thin piece of plastic to insulate that spot in case something caused the board to touch the sink again. Then I found that the other guy had missed a screw hole on the anodized insulator and scarred the insulator, so that was fucked. I cleaned it up and then applied a layer of sil/kapton tape and reinstalled. Washed the sink up and buttoned her up. It came out pretty good. I am glad I finally got it.

Also, I found some good subs for the pre-drivers. I don't recall the number off hand, but if someone needs it, let me know and I will dig it up.

Here are the pics:













Later,
Jason

[trickyricky]

Am curious to what predrivers you used, I have a few NOS in stock but would be nice to know for a suitable sub.

[Jacampb2]

Am curious to what predrivers you used, I have a few NOS in stock but would be nice to know for a suitable sub.

Sure, no problem. I just looked them back up. NPN:KSC2690AYS(clicky for Mouser). PNP: KSA1220AYS(clicky for Mouser).

Hope this helps. I also found another good pair of pre-drivers. The ones above are probably good for almost any but the biggest PG. I haven't actually looked at a Ti/ZX amp in a few years, so I am not 100% sure, but I don't think their rails were over 50V on any but the really big TIs. I have a set of pre-drivers I found which should work well if the amp has much higher rails. The KSA1381ESTU/KSC3503ESTU. However, I have not been able to find the KSC3503 readily available in the "E" beta range. I actually bought KSC3503DSTU. There is some overlap in the two beta ranges. My plan is to gain match them. I have a transistor tester and it should be easy to find matched pairs if they exist.

Later,
Jason

[Stravus]

Damn nice repair, I purchased a 1.5x one time that had the sub section burned out of it. So ended up getting a donor put in from TrickyRicky

[kg1961]

man that's a lot of work for a cheaper amp like that. mad skills but not sure if it was worth it

[Jacampb2]

I got the amp for next to nothing and I probably only put $15 in parts into it. This is only a hobby, so I won't put a value on time. As for a cheap amp, well, it was a inexpensive PG amp, but I would not call it cheap. It had limited x-over capability but was probably ahead of the competition at the time. It also wasn't seriously underrated like its bigger brothers, but with a pair of BJTs on each output I would guess it put out nearly the exact RMS power that they claimed. It is also a three stage output just like all of the PG non mosfet amps and seems to be built to a spec, but it wasn't any bullshit like the "Profiles" or "Pyramid" amps of the same time frame.

Personally I think any PG amp brought back from the brink is money and time well spent! If not for keeping a legend alive, then just for the sheer puzzle and deduction necessary to troubleshoot and repair.

Later,
Jason