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APEX JR. subwoofer amp blowing fuses, bad caps found

timsch

Feb 4, 2023
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Please post what data sheets you have there so we don't have to go searching.
Show what meter range you measured the semiconductors on.
Both datasheets were hyperlinked in my previous post.

I used the diode setting on the Fluke 177 which is auto-ranging.

Bridge is ok. Transistor seems ok too (the schematic link you give shows different designations than on your actual board i.e. schematic shows Q105/Q106 but the board is marked Q409 and .... dunno, can't see!)

Yeah, I was never able to find Q105/106 printed on the board either. Doesn't help things any.

Post #14 showed another sick-looking component. Any thoughts on the appearance?
 

timsch

Feb 4, 2023
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The info I found online regarding in-circuit testing of ICs indicated "may" have to remove, like in post #13, so these tests are done in-circuit using Fluke 177.

Transistor Toshiba C5198/A1941
V_BC = 0.580 / 0.525 V
V_CE = (0.585/0.838) / (0.533/0.874) V (values differed when switching multimeter probes)
V_BE = 0.996 / 1.001 V

Bridge RS402L
Pin 1-2 = 0.536 V
Pin 1-3 = 0.544 V
Pin 1-4 = 0.982 V
Pin 2-3 = OL
Pin 2-4 = 0.544 V
Pin 3-4 = 0.529 V

The transistors both measure within spec according to the datasheet. The bridge I'll need y'all's expertice on.
Apologies, but I believe that I likely assigned the values for the transistor measurements to the wrong pins. I'll have to verify when I get home later today.

Here are some pictures of resistance measurements I took from the area of the board where the dried substance covers it. With some areas measuring less that 1 MOhm, it seems that it could be generating shorts wherever it flowed.

IMG_20230207_223816447.jpgIMG_20230207_223724832.jpgIMG_20230207_223756819.jpgIMG_20230207_223740287.jpg


EDIT: changed kOhm to MOhm
 
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kellys_eye

Jun 25, 2010
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Values in the Megohm region aren't a particular issue - the capacitors really need their ESR testing before we go off on a wild goose chase.
 

timsch

Feb 4, 2023
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You seem terribly worried and distracted by the glue issue.
Forget it and move on.
Dude, I'm not terribly worried about $hit as far as this goes, I'm just trying to get to the bottom of things and am providing any info I think might be relevant - in this case something was present on the board that didn't look like it belonged and was conductive, so I threw it out there.

I don't deal much with electronic components on this level, but I do deal with glue, and if this is glue, it's a piss poor job of it, given that it wasn't under the caps, the caps pulled right off without any effort at all, and I was able to scrape it off the board surface easily with a small screwdriver. It also doesn't match any of the other adhesive they used all over the rest of the board.

Say what you want, but I still say it's melted cap skin. Doesn't really matter since the problem lies elsewhere apparently and I'm happy to leave it at that.
 
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timsch

Feb 4, 2023
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I redid the measurement for the transisters, in-circuit, since I screwed up the pin ID the 1st time.

5198
red/blk
blk/red
Vbc​
0.588​
OL​
Vbe​
0.842​
0.589​
Vce​
1.02​
1.02​
1941
red/blk
blk/red
Vec​
0.534​
OL​
Veb​
0.543​
0.881​
Vcb​
OL​
1.02​

Picture shows MM probe connections. Reading of 0.588 was measured with red probe on base & blk probe on collecter.

IMG_20230208_164911139.jpg

Looking at this link, measurements from C-E for 5198 show it to be bad. Is this conclusive, or do I need to remove it from the board to be sure?


Edit: I just saw that the 1941 has the opposite pin configuration as the 5198, so I just relabeled the Vxx in the table above. Here is the datasheet for it
 
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timsch

Feb 4, 2023
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I removed the transistors. Here are the readings. Seems to match the datasheets. They're good, right?

5198 – isolated
blk/red
red/blk
Vbc​
OL​
0.589​
Vbe​
OL​
0.589​
Vce​
OL​
OL​
1941 – isolated
blk/red
red/blk
Vbc​
OL​
OL​
Vbe​
OL​
0.525​
Vce​
OL​
0.514​

On the table in the post 28, I had the blk/red labels reversed. The way I measured them was as shown in this table above.
 
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kellys_eye

Jun 25, 2010
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Nope, those readings look ok to me.

Gluing capacitors to the board is common practise given their physical size and potential for movement. Whether or not the black gunge is the actual glue is debatable - not something I can go into in detail without seeing/smelling it for myself (capacitor gunge from leakage has a known 'scent' that experienced engineers can sniff out).

Using the white silicone adhesive is, however, a common method but since it WASN'T used on the big capacitors it seems reasonable that some other version of glue was.

The capacitors DO 'look' to be ok, they measure the right value but their ESR may be the main cause for the problems you're seeing - that said there are other potential problem areas that would need to be isolated individually to prove otherwise. There are two low voltage regulators (each on their own heatsink) either one of which may have gone dud, the main amp driver device (chip) could be shorted etc. Best way forward would be to test the ESR and refit if ok, power up again BUT with the two low voltage regulators isolated, the amp chip isolated and the output transistors removed then fit/test the bits/sections going from the main smoothing capacitors to the output transistors.

Somewhere along that route you will discover the PSU powering up properly, no fuse blowing etc. This might all be possible by selective removal of PCB link wires and/or track cutting but I won't go there as it would take an age - it's something quite easily resolved with the right application but I'm sure, if you keep up the determination, you will get there yourself anyway.
 

timsch

Feb 4, 2023
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I looked into testing the ESR of the caps; this may be beyond the limit of what I'm able to do. I have only basic electrical diagnostic knowledge & equipment.

I removed the two components from their individual heatsinks. There were no markings on them but the board lists them as IC104/105 and the schematic shows them to be 7815 / 7915. I measured them as I did the transistors. I numbered the pins left to right as viewed in the picture for both sets of voltage readings even though the ground-input-output order is opposite from each other.

IMG_20230209_093841935.jpg

IC105 – isolated
blk/red
red/blk
1-2​
0.654​
OL​
1-3​
0.826​
OL​
2-3​
OL​
0.581​
IC104 – isolated
blk/red
red/blk
1-2​
0.546​
OL​
1-3​
0.547​
2.338​
2-3​
OL​
0.689​
 

kellys_eye

Jun 25, 2010
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kellys_eye

Jun 25, 2010
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If you can't do the ESR test then just purchase new capacitors - they're probably cheaper than buying a tester.....
 

timsch

Feb 4, 2023
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If you can't do the ESR test then just purchase new capacitors - they're probably cheaper than buying a tester.....
I just bought the tester. I'm quick to order new tools, particularly when they're inexpensive & well regarded, which this seems to be. It should be here on Saturday. I'll see whether there is even enough pin left to check with this tool....
 

Bluejets

Oct 5, 2014
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Nope, those readings look ok to me.
Op should not be getting a collector to emitter reading for 1941 as in #29 nor should there be an open on the base to collector in both dirtections.
Haven't looked any further as Op apparently is getting confused as to just what is being measured where.
I'll leave it to you to sort out but in my mind you have to start there and rectify that first.
 

timsch

Feb 4, 2023
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I just bought the tester. I'm quick to order new tools, particularly when they're inexpensive & well regarded, which this seems to be. It should be here on Saturday. I'll see whether there is even enough pin left to check with this tool....
Finally got one working. Here are the readings of the low voltage regulators that were on the individual finned heat sinks

IMG_20230217_145159657.jpgIMG_20230217_145223952.jpg

And here are the large electrolytic capacitors

IMG_20230217_153325274.jpgIMG_20230217_153259225.jpg
 
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timsch

Feb 4, 2023
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I back-burnered this a while due to other issues, but got back to it yesterday, putting it back together, made all connections & powered it up again with a new fuse. This time I watched the component side of the board when I did and it did immediately blow the fuse and the transformed sparked on the coils on the opposite side from the output wiring. Next, I disconnected the transformer wiring connection from the board and powered it up again with a new fuse and the fuse did not blow. I then checked the voltage across the transformer output wires going to the bridge rectifier and got readings ~ 5mV.

I assume this means that the transformer is shorted. If it's shorted, does it make sense that the fuse would blow with the connection being made and not blow without the connection made? I was not able to find any information on the transformer (shown in post #3) searching for the model # HK86H-103 / TTJ1201-001
 

Martaine2005

May 12, 2015
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Yes, sounds like the transformer is shorted. . I presume you checked the bridge rectifier?:
Edit: check the bridge first.

Martin
 

timsch

Feb 4, 2023
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I contacted the supplier of the amp and they don't have any datasheet on that old transformer. Looking at how to test transformers, knowing what the specs are was always stressed, but without specs, am I SOL or can something still be done?
 
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