Replacement filter caps for AU-919

Phono board progress. Still waiting on some resistors and the 680uF caps.

This glue was by far the worst I've had to remove. I scraped at it with a filed down nylon o-ring remover and used acetone to soften and remove with q-tips.
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After cleaning. I had to remove several of the resistors.
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After replacing many of the components. See where the glue ate away at the paint on the heat sink? Also, can anyone spot a couple caps I failed to remove?
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The heatsink in this board tends to run quite hot. I am not srure if this is to be expected or if it is due to degradiation of some of the components. In the unit i have, the power supply board F2844 runs hot also which i suspect it is related to this. I would like to know what is your experience with these issues and if you find any solution to them.
 
I would like to know what is your experience with these issues and if you find any solution to them.
That heatsink doesn't get very hot in my opinion, so I think you might have a problem with yours, but it really depends on one's definition of 'hot' :)

At first not remembering the board number I thought you meant the F-2835 (MM Eq) board (pictured above) which does get hot in my opinion but it is part of the design. More important in my opinion is the periodic DC offset drift on the output of this board which can be at least 50mV and maybe more like 100mV on some examples. It seems to roughly observe the 'set point' but drifts up and down all the time. I have a possible (simple) fix for this pending for when I get time to implement it, I will of course post details of it in due course if successful.
 
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Onto the driver board, but first, some pics of the MC head amp:
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Here's a close up of R39 and R40 where I replaced the original 33 Ohm ones with 330 Ohm ones.
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The driver board glue damage:
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An eaten leg from one of the PP caps:
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Almost done with this thing. I stupidly ordered the wrong trim pot for the driver board. I ordered a 100k ohm one instead of 1k. Mouser seems to have duped me with the Panasonic FM 120uF 50V caps I ordered. They indicated that they were 5mm straight leads, but what I got were crimped leads. I didn't like the way they sat up from the board, so I replaced them with 100uF Panasonic FCs. They might not be quite as good as the FMs, but I think they'll do.

The FMs I got from Mouser:
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And the FCs I later installed. I think these are a much better fit:
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The full monty. Notice the missing bias trim pot?
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Here are the new relays on the protection board:
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The other side of the protection board:
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Nice work and great thread!

re: the crimped leads on the FM's, would there have been enough lead length for you to trim the leads pre-crimp and solder them into place?

Regardless, the FC's are fine caps and will do the job perfectly.
 
Nice work and great thread!

re: the crimped leads on the FM's, would there have been enough lead length for you to trim the leads pre-crimp and solder them into place?

Regardless, the FC's are fine caps and will do the job perfectly.
Thanks! I think on those FMs the leads at the base are only 3mm apart. I could have made them work, but I had the FCs that were the right fit, so I just went with those instead.

Leestereo recommended 120uF caps in those spots, but I think in this case, the 100uF ones will work just fine.
 
I could have made them work, but I had the FCs that were the right fit, so I just went with those instead.
Good decision :thumbsup:

Lead spacing often features very strongly in my choice of capacitors of all kinds. ;)
 
Thanks! I think on those FMs the leads at the base are only 3mm apart. I could have made them work, but I had the FCs that were the right fit, so I just went with those instead.

Leestereo recommended 120uF caps in those spots, but I think in this case, the 100uF ones will work just fine.

Ah, I see exactly what you mean! Thanks for the explanation. My eyes/brain weren't cooperating at first.
 
So, I just realized that along with all the missing screws, I'm also missing the bracket that secures the flat amp. At first I thought I'd just use a zip tie to secure it, but then I thought about fabricating one. I don't have any proper tools for this kind of work, so I had to use aluminum. Here's the end result:
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I got the AU-919 running. Did all the adjustments. The only problem I'm getting is with -10V adjustment on the left channel of the MC head amp. I'm getting zero volts on that side with no ability to adjust with the trim pot. I can get +10 and - 10 on the right channel and +10 on the left, but no -10V on the left. Does anyone know a common cause for this problem?
 
Does anyone know a common cause for this problem?

The regulators (or rather 'capacitance multipliers') supplying these voltages are located on the MM Head Amp PCB - you may have a failed component or perhaps more likely (as you have '0' Volts) - a broken connection from the MM Head Amp to the MC head Amp. Now that I have double checked I see these connections are via the multi way connector at the back of the MM Head Amp PCB F-2835, measure for -10V on pins 113/114 on the MM Head Amp, and then on pins 12/9 of the MC Head Amp to check for presence of that -10V ;) (sorry, I previously advised they were carried by the black ribbon cables, which is not correct).
 
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Ok, so I took some measurements.

First the MC head amp F-2833:
11 29V
15 30V
13 0V
17 -30V
09 28V

10 .7V
16 29V
14 0V
18 -43V
12 28V

Then on the MM head amp F-2835. These were taken with the connector removed. The interconnects are individual stranded wire, not solid ribbon cable.
106 43V
108 42V
110 7V
112 -43V
114 7V

105 43V
107 43V
109 Starts around 1.8 and then drifts down to 1.1V
111 -43
113 -42
 
OK, there is a multi way plug as well, I can see now on checking that it carries those connections. Those measurements indicate something odd going on - have you tried adjusting the trimmers on the MC Head Amp Board?

Note that you can't make meaningful measurements with that multi-way connector removed - as the trimmers that adjust the voltage you are reading are located on the MC Head Amp, and the transistors they control are on the MM Head Amp - thus the connector must be plugged in. ;)
 
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I was able to adjust all the voltages with the trim pots except for the -10 on one of the channels. I suspect a bad transistor on the MM board, but I'm a real novice when it comes to troubleshooting. I'm more of a shotgunner.:)
 
I'm more of a shotgunner.:)
Not sure which channel we are talking about so I'll give you the likely component numbers affected for both. :)

OK, well measure R107 or R108 - (whichever one it is) - should be 100Ω, if ok then, a continuity check between pin 111 or 112 (on F-2835) to ground with your multimeter on 'Ω' - and check that the respective MC board trimmer (VR05 or VR06) on the F-2833 board actually adjusts. If ok - then take out TR107 or TR108 - whichever one it is - and check it with the '6 way test' using your multimeter on diode check (or a transistor tester if you have one) - if ok move on to the next i.e. TR103 or TR104 and do the same thing. I am thinking the fault should be obvious as you have 0V output from the 'regulator' - so an open circuit junction (maybe C-E) is likely.

If any of that doesn't work as expected/described above, or you can't understand - let us know and we'll advise or otherwise explain.

OR - just shotgun those parts above :(
 
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