Advent 300 No Worky

Discussion in 'Solid State' started by Superman541, Aug 26, 2017.

  1. stereoguy70

    stereoguy70 AK Subscriber Subscriber

    Messages:
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    Location:
    Salem, NH USA
    The ceramic capacitors are factory as is the black "lamp cord". Those other resistors I'm not so sure of them being factory as I have never seen a 300 with resistors mounted to the backside of the boards, and that melted heat shrink tube is a sure sign of a hack-job repair previously. As far as the 1000uf caps you got, I wouldn't use them. Not enough filtering capability for the power supply. I wouldn't use less than the factory specs (3000uf IIRC), as you may end up with more problems than you already have......even for "testing purposes"......
     
  2. northpaw

    northpaw Active Member

    Messages:
    156
    Location:
    New England
    I agree with stereoguy. Everything is stock except for those two resistors and the bungling around the heat shrink (that resistor is otherwise stock). The bungling is unattractive, but hopefully the hack job was effective (it may or may not be). And as for the caps, even if the caps you got were 3000µF, you would still need to verify they have a sufficient voltage rating. Never install a cap with a lower V rating.

    So I think the plan that Alan outlined is still the best course; just try to get that resistor in there and see what happens. On your fat-tipped iron, if a screwdriver-shaped tip, you can use a corner. Best to clean the tip well before use: melt a good dose of fresh solder onto it, and immediately wipe clean with a moistened sponge (never use that sponge for any other purpose after that) or a thick wad of moistened paper towel (thick enough so you don't burn yourself). Repeat if needed. Make sure you use rosin-cored solder, and if you have separate flux, all the better.
     
    stereoguy70 likes this.
  3. Alan0354

    Alan0354 Super Member

    Messages:
    2,090
    Location:
    Bay Area
    I have nothing to contribute on the pcb, never seen this amp before, I am kind of working on this at 10,000ft high in the air from a long distance!!! Only by the schematic.

    But I have some off topic comment. Depending whether you just want to fix this amp and move on or you are taking restoring and repairing as a hobby that's going to last for years to come. If this is a one time thing, see whether you can borrow a good soldering iron from a friend to work on this project. If you plan to get into restoring, but a better soldering station. The soldering iron make or break your amp!!!! I am born cheap, I am cheap on everything EXCEPT the soldering iron. Your 30W one is going to ruin the pcb and that spells the end of the amp.

    If you are to do this often, buy at least a Weller Station like this one:https://www.amazon.com/WTCPT-Temper...413&sr=8-16&keywords=weller+soldering+station

    I like this over the newer ones with knobs as this is higher power. Ebay has it a little cheaper. DO NOT get the more common names like Aoyue etal. Stay with the best like Weller and Metcal. These are industry standard....for very good reason. I personally have 3 soldering iron, the Weller above that I have over 30 years of experience, a Metcal M500 ( really really expensive) and the Aoyue rework station with fume absorber and desoldering iron. I cannot tell you how much I hate the Aoyue, only reason I have that is because I am extreme allergic to the smoke. I have to use it whenever possible. The iron cannot hold heat regardless of big or small tip. It doesn't not work on two or more layer pcb. Another thing that is more annoying is something to do with the metal of the tip, the Aoyue is slow on melting solder, you have to push hard and hold for a sec or two. My other two never have problem, as soon as the tip touch the solder joint, the solder melt. It's almost like the tip of Aoyue forms a layer of oxide and heat conduction is bad. Sadly the tips of Aoyue is used by other brands like Hakko, so as long as it's this type of tips, you might have problem.

    Bottom line, borrow or spend the money.
     
    Last edited: Aug 29, 2017
  4. Superman541

    Superman541 Member

    Messages:
    90
    Thank you. I don't have separate flux. The tip is conical. I will surely clean it good first. The caps are rated at 50V. Nichicon. My friend says failed caps can cause other problems and also, surely would be noisy....likely leaking AC. I recall a suggestion that I check for leaking AC. Yes, rosin core solder.

    Thank you for reporting that most of these bits on the underside of the board are likely factory. I'm satisfied that it makes sense to proceed. I also intend to stay with the original plan of first getting this thing to run at all, and then go from there. I also recognize the wisdom of, once the unit is running, replacing all the caps. At first though...baby steps.

    Yes, I need a good soldering iron or station.

    I am leaving for a week and will resume the project upon my return. I might also be picking up a pair of Large Advents on my trip. They, and this Model 300, have excellent reputations.
     
  5. Superman541

    Superman541 Member

    Messages:
    90
    It Lives! I installed the 47K resistor. I hesitate to show you a pic of the despicable soldering job, though I am confident I did not damage the board and I got a good connection. Hooked it up to a power amp and the preamp works!!!

    I got a CHEAP soldering iron at a store I almost never patronize because the tip on my Radio Shack unit is pretty fat. I could NOT get the new soldering iron to tin, but I coaxed it into doing the job.

    I have many questions. About soldering irons and technique and such. And also about next steps on this Advent 300. I envision replacing the filter caps now and perhaps just getting some solder braid and a handful of smaller caps and move forward on the refurbishing work. But I just wanted you folks to know that the plan worked. Thank you Alan, Northpaw and others who helped. I am very grateful. And happy.
     
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  6. Alan0354

    Alan0354 Super Member

    Messages:
    2,090
    Location:
    Bay Area
    That's what I suspect, you lost the Q402, the resistor proofed it. You need the -15 for everything, that's why nothing works when that failed.

    It's up to you whether you want to replace the Q402 or not. I tend to replace Q402, I like to keep things original. Few years later, you'll forget this whole thing and if that fails, you don't know why the resistor is there and nobody can help you as it's not in the schematic.
     
  7. Superman541

    Superman541 Member

    Messages:
    90
  8. Superman541

    Superman541 Member

    Messages:
    90
    Thank you so much, Alan. Truly.

    I am inclined to replace that transistor, as you suggest. (although...resistors are pretty reliable) As I say, clearly the visibly failed filter cap in the power supply and its buddy need changing. I think the various smaller caps are also a good idea to replace as well. I am, however, as I have reported, timid and ignorant when it comes to electronics. I fear damaging the board, or damaging components like transistors during installation. That said, I am smart enough to know some of the dangers. I have a lot of learning to do, but I am very grateful and comforted to know that I can get help here.
     
  9. Alan0354

    Alan0354 Super Member

    Messages:
    2,090
    Location:
    Bay Area
    You are welcome. If the filter cap spilled it's beans, you got to change it. I would hold off on the smaller caps unless it looks bad. If you really want to play it safe, measure to make sure you have good -15V, then leave the resistor there and don't change the Q402. Write a note and tape it somewhere inside the amp to remind you in the future that's what you did.

    Yes, the less you mug with the pcb, the better. This hold true even for me that have all the equipment and experience. I build my amp, I don't use the first pcb I built, test and characterized as I feel I work on it too much already. After I debug and bring the board up, I build two more new boards, and those are the two I put into the final amp build.

    I always believe and hold on to the theory that if it's not broken, don't fix it. I have seen people here can't leave the good thing alone, pull out transistors and replace them on a working amp, then they make some mistake and it doesn't work anymore. I make it a point not to help those because far as I concern, they ask for it.
     
  10. northpaw

    northpaw Active Member

    Messages:
    156
    Location:
    New England
    Well, so glad it works, and kudos to Alan for putting the finger on Q402 and coming up with an easy path to verify that it was the problem.

    You've got to replace the two large axial caps because they are leaking. Remember to get axial caps, esp. because the soldering effort will be much easier. I suggest you hold off on any "optional" repairs until you get more practice with, and develop more skills with, soldering.
     
  11. Superman541

    Superman541 Member

    Messages:
    90
    Report:

    Alan says if it ain't broken, don't fix it. Though I have little experience with electronics, from first hand experience I know the wisdom of this advice. I will replace the filter caps, as Northpaw mentioned. Meanwhile....

    what they say about the phono section in these 300s is true. Magnificent.

    The lights and switches I have used are working. The radio brings in some stations with real good clarity, though there is no antenna. I'm pretty pleased and so is the lady of the house. This is a very nice little workhorse. The sound is really good. I've used iPod (AUX), Phono and Tuner. AUX sucks compared to Phono and Tuner, but that's probably just a source problem.

    Perhaps one day I will use it as a full receiver and see what happens.

    Did I happen to mention how thankful I am for the help?
     
  12. northpaw

    northpaw Active Member

    Messages:
    156
    Location:
    New England
    I'm glad it is sounding so good, and you're welcome for any help I provided. I feel fortunate for having bought my unit back in 1977 and having it establish my personal bar for sound quality quite high.

    On the iPod, it should sound decent. It will sound best if you tap the line-out (via the 30-pin connector in older units; not sure what options are available via the Lightning connector). If you connect via the headphone port, best to turn the iPod volume up to 80% or so (some suggest 100%) and do all further volume adjustment on the 300.
     
  13. Superman541

    Superman541 Member

    Messages:
    90
    Alright, I am ready to place an order for the filter caps in the power supply. I see a Nickicon that is axial, 4700 uf, 50V. Stock is Mallory, axial, 3000 uf, 30V. The Nickicon appears to be a size that will physically fit in the same location. Am I covering my bases here?
     
  14. Alan0354

    Alan0354 Super Member

    Messages:
    2,090
    Location:
    Bay Area
    If the 4700uF 50V fits, get that one.

    Can you hold off for a day or so. You talked about SS amp sounds bad clipped. I want to look to see whether there is any easy way to put a schottky diode to prevent your amp from clipping and see whether you can hear any difference.

    Normally it's not that simple to design in anti-saturating diode circuit, but your amp only has +/-22V rail, that make finding a diode to do the job easier. I am busy today, I have to look at it later or tomorrow. Can you wait a day or so to see whether you want to try......and if I can find a diode to do the job.
     
    Last edited: Sep 9, 2017
  15. Superman541

    Superman541 Member

    Messages:
    90
    Yes, I will wait. However, I am using only the preamp section of this receiver. Running it through a Mitsubishi DA-7DC (70 wpc). Clipping, I assume, would be the Mitsubishi.

    In my posts on the other thread, I am assuming it is clipping that I hear. The sound starts to get scratchy/edgy, even at medium volumes. Harsh. Very subtle though, at medium volumes. It's not a big problem. It's just there.

    With decent tube gear, even though there may be clipping, it is simply not there. Lots of people don't hear what I hear, Alan. I'm just whiny, I guess.
     
  16. Alan0354

    Alan0354 Super Member

    Messages:
    2,090
    Location:
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    It is even safer if you are not planning to use the power amp in the future, you don't have to worry about screwing it up. Just listen to it loud ( to distortion) before and after the modification.

    Advent power amp.JPG

    Advent power amp1.JPG

    The diode you order is either:

    https://www.digikey.com/product-det...odes-division/SD101A-TR/SD101AVSCT-ND/3104398

    https://www.digikey.com/product-detail/en/stmicroelectronics/1N6263/497-2508-1-ND/603890
    You modify both channel as shown. It is not going to work as well as what I have custom designed as it has more components. But the diode should prevent the Q304, 305, 306 and 307 from all out saturation even with this simple modification. YOu only need to get 4 diodes ( well maybe one for good luck!!!). Let me know whether you can hear any difference before and after.

    If you are not going to order from Digikey, let me know where you want to order and give me the website, I can choose diodes from the place you want to order.

    Alan
     
    Last edited: Sep 10, 2017
  17. Trojan4Life

    Trojan4Life Active Member

    Messages:
    377
    Alan IS the man!
     
  18. Alan0354

    Alan0354 Super Member

    Messages:
    2,090
    Location:
    Bay Area

    Ha ha, I won't speak it so soon. This is a quick and dirty way to experiment.

    Problem with BJT saturation is when the base collector diode reach about 0.7V and turn on. Once it turns on, it takes time to turn off. They means it takes time for the transistor to come out of saturation. We called it sticking to the rail. The whole point is to keep the collector of Q305(Q304) from going 0.7V above the base, and collector of Q307(Q306) 0.7V below the base to prevent the base collector diode from turning on.

    Schottky diode has a turn on voltage of about 0.4V at low current. The schottky diode I put in literally in parallel with the base collector diode of the transistors so before the base collector diode reach 0.7V and turn on, the schottky diode already turns on and prevent the base collector diode from turning on.

    But with this simple add on, the base collector diode still has 0.4V, which is close to turning on. So the result is not as good. It might not be good enough to hear the difference.

    The better fix is like in my design where I keep the Vbc never more than 0V, so the base collector diode never comes close to turning on as shown:

    Saturation clamp.JPG

    If you look at Q44 in the schematic. I label the voltage Vb at the base of Q44. This means base Q45 is 0.7V BELOW Vb. D32 is the clamping diode to prevent the base collector diode of Q44 from turning on. So when D32 has 0.7V across it and turns on, the collector of Q44 is still at Vb, never goes above Vb. This means the voltage across the base collector diode of Q44 never goes above 0V and never come close to turning on.

    the circuit for Q50 is the same idea. this would be too complicate to modify into the existing amp. So we just hope for the best. Only about $2.00 to try, if it does not improve, we just laugh it off.

    But if it improves, OP might be happy just using the whole amp!!!

    I want to emphasize, this is a very old idea used in Schottky TTL design for over 40 years. Nothing original here.
     
    Last edited: Sep 10, 2017
  19. Superman541

    Superman541 Member

    Messages:
    90
    I have no idea what Alan is suggesting (he is a rockstar, I am not), but I can probably find the locations for those diodes. Using the two images, from the Advent schematics, which he posted at 12:51 yesterday (according to my screen). And I think diodes are directional, so when they are here I will need more coaching. Perhaps they could also go into the Mitsubishi DA-7DC power amp. Only....perhaps different values. For the Mitsubishi they would be different values....right?

    For the filter caps, here is the Nickicon I picked out. It is 52mm long, which I believe will fit:

    http://www.mouser.com/ProductDetail...GAEpiMZZMsh%2b1woXyUXjyNiHXRKgpUDESGiUfuUV2Q=

    Here is the Nickicon 4700uf, 50V cap I found at the Digikey site, and the spec sheet:

    https://www.digikey.com/products/en...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

    http://nichicon-us.com/english/products/pdfs/e-tvx.pdf

    From these, I cannot tell the length. These are probably also 52mm, but I just don't know. Can anyone verify that these caps will also fit. That way, I could order the caps and diodes from the same place.
     
  20. Alan0354

    Alan0354 Super Member

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    2,090
    Location:
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    Those diode can only use up to 65V max, you amp is +/-22V, so the max voltage swing is 44V. If you other amp is +/-30V or over, then the diode will not work. I have to find a higher voltage diode, but it's hard to find a schottky diode that is over 80V.

    Yes, when you get the diode, I will try to help you again.
     

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