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Help with SX-1980 New AWR-154 Board pleeeeze

Discussion in 'Pioneer Audio' started by Cheddar Bob, Aug 7, 2018.

  1. Cheddar Bob

    Cheddar Bob New Member

    Messages:
    6
    Location:
    BloNo, IL
    Hi AK folks. Long time lurker, first time caller! I'm normally a vintage tube audio guy but couldn't resist a 30 buck SX-1980 at a garage sale maybe 15 years ago. It has the typical toasty power supply board with much of the foil hacked up by a PO. Back then, I couldn't find a used board to rework, so it went to the "someday" shelf.

    A few months ago I stumbled on one of these slick new boards on ebay from txturbo and went for it. It looks like a great piece of work and I understand several here put in their two cents, so I hope I've come to the right place!

    I now have the new board by txturbo installed and i believe the wires are where they belong. But before I try to give it a go I'd like some direction on the resistance measurements I got as it looks like some are off. I've listed just the weird ones. Wires not listed measure per the instruction sheet.

    Measured resistance to chassis ground

    W3 30.8k, should be 36k
    W8 seems to act like charging a cap, never goes full short like instruction sheet lists
    W13 56.6 ohms should be 214 per instruction sheet
    W14 56.6 ohms should be 101
    W22 2.0 ohms, should be 2.8
    W23 2.0 ohms, should be 3.0
    W20 .6 ohm should be 1.5
    W19 .6 ohm should be 1.5
    W24 .2 should be 1
    W25 .3 should be 1

    A little more info.. .
    There is a chance I have a wire swapped on W13 and W14. There is one on 13 and two on 14 and they're all pink. But I don't think it matters since the board ties them together, right?

    Also, I've replaced the 22,000 uf power supply caps, and replaced caps on GWH-109 and GWH-110.

    If it matters, on the original Power supply board, the two 1A fuses were blown. The others were not.

    I suspect there are things going on with some of the other boards but I haven't gone down that road yet. Judging from the dust on them, they appear to have never been touched.

    I'd appreciate any tips or being pointed in the right direction.

    Thanks! Dave
     
    Last edited: Aug 8, 2018

     

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  2. macyjrm

    macyjrm AK Subscriber Subscriber

    Messages:
    1,206
    Location:
    Mississippi
    I’m not a tech so I can’t add any real value to your thread. I am certain you are going to be very happy with that new power supply. It’s like a new engine in your classic car.
     
  3. rcs16

    rcs16 Super Member

    Messages:
    3,893
    Location:
    Baldwin, Ontario, Canada
    W13,14, 13.5V supply, big schematic shows 250mA draw, so that is an effective 6 ohm load. it could depend on the source selector, what position does the instructions say for it to be in for these measurements? try to change to AUX,Phono to see if it changes?
    I have a 1980 in for ecap service, so I can check a few things out in my unit, since I was told it works.
    What 1A fuses are blown on th eold PS pcb? one set are for the +/-100V and the other for the 25V unregulated supplies.
    iirc the txturbo uses terminal blocks for the connections to the loads. if so I would wire up the PS to its unregulated supplies and leave the loads disconnected first to see if you get proper regulated voltages.
    W24,25 are the dial lamps
    Some voltages like the W15(5V) rely on a load current to be drawn to derive the correct V as shown on the schem.
    At times if you reverse the ohmmeter leads you will get a different reading as different conduction paths come into play such as in the case of W8.
    make sense of what supplies go where and the ckts involved. Like W8, wire "Y", it goes to the pwr meter ckt, it has two 15K ohms as the first connections which go to diode clamps, D9,10
     
  4. Cheddar Bob

    Cheddar Bob New Member

    Messages:
    6
    Location:
    BloNo, IL
    Thanks for the reply. I'll check the selector switch and see if moving it makes a difference, or swapping the leads. The instruction sheet that came with the board did not give info on what the switches needed to be set on prior to testing the resistances. But if I do seem to recall seeing mention of that in the service manual for the receiver somewhere. I'll see what I can dig up. The instruction sheet for the board does give a warning about powering it up without the resistance measurements and the rest of the unit being tip top, so I'm a little chicken to run it, even without the loads. And maybe I'll take a quick look at the boards these wires go to. I know W3 runs to GWH-109 or 110 and the corresponding wire to the other board gave a good 36k ohm measurement. So I'll probably poke around on the board for W3. I've already recapped it, so it's possible I botched something there. I'm also a little concerned about those transformer wire readings being so low too...

    The fuses were fuse 1 and 2 on the big schematic, can't recall the pin numbers (at work now) but they connect to the orange transformer leads.
     
  5. Cheddar Bob

    Cheddar Bob New Member

    Messages:
    6
    Location:
    BloNo, IL
    Man, you're not kidding. I'd basically given up on this thing and it sat on the shelf for 15 years because I just did not have hope that a rebuild of the old board was going to work out or last, especially since it had been hacked on at least once prior. I had a side hustle for awhile were I repaired vintage coin op video games and I'd been into enough fried/burnt/warped PCB's and monitor boards and power supplies to know it was a dicey proposition at best. So when I saw that thing on fleabay, it was a no-brainer. Now I just have to figure out how to catch up the rest of the thing to behave!
     
  6. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,817
    Location:
    Las Vegas Nevada
    Unplug both amp boards. There's plugs on top and bottom of the boards.
    If you don't have one build and use a DBT before powering up.
    Double check your work many times with breaks in between. Maybe a buddy cross check if you still feel a little rusty.
    Many times there are issues after the power supply is restored. Test the lamps and tuner once operating then plug in the amps one at a time checking for proper voltages and amp settings. Remaining on the DBT every time a new load is added - until everything checks out.
    The turbo boards are installed in a 1980 and checked before they ship so you can be assured it will work.
     

     

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  7. Cheddar Bob

    Cheddar Bob New Member

    Messages:
    6
    Location:
    BloNo, IL
    Thanks Zeb. I'm assuming a Variac will do instead of a DBT??
     
  8. kevzep

    kevzep Its all about the Music

    Not really, the DBT offers current limiting which the variac does not, you'll get to a point winding the variac and then suddenly various semiconductors will turn on and if there's a problem, nothing will save your amp....

    I have a DBT with a 120 watt bulb, it does most things, a 60watt bulb with give you plenty of current protection
     
  9. Cheddar Bob

    Cheddar Bob New Member

    Messages:
    6
    Location:
    BloNo, IL
    Good point. Maybe I'll build one after all these years!
     
  10. rcs16

    rcs16 Super Member

    Messages:
    3,893
    Location:
    Baldwin, Ontario, Canada
    Definitely need one. On mine I have a power switch and a lamp bypass switch.
     
  11. kevzep

    kevzep Its all about the Music

    Funny you mention that, I was about to wire in a bypass switch!!!
     

     

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  12. KingBubba

    KingBubba "Too Much Stuff" Subscriber

    Messages:
    9,790
    Location:
    Brooksville, Fl.
    Aside from being useful, the DBT also costs you very little. I usually start with a 60 w then go to 100 w. With the 1980, you might need to go to 150 w. I wish you luck on finally getting the beast fired up. I don't think I could even pick it up. Many years ago I met a guy to buy my 1250. He stepped out of his car with a parrot on his shoulder. He also had a 1280. I ended up getting the 1250 and 1280 both for $500. He also had a 1980 below the other two. He offered it to me for $500. I passed on it. As you can imagine, I am still kicking my own butt. Enjoy your beast.
     
    Last edited: Aug 9, 2018
    mattsd likes this.
  13. txturbo

    txturbo AK Subscriber Subscriber

    Messages:
    919
    Location:
    Austin, TX
    I did not record the switch settings when I did the measurements so that may impact the readings. :eek:

    I just took a look through my pictures at the current draw readings once the receiver is on and stable. At 115VAC it's .74A. You can see it in the upper right of the picture. I have a another reading that shows 1.2A RMS using a different instrument once it's stable.

    [​IMG]


    Inrush curent test:
    After a few tests the highest recorded current was 17.1A.
    The inrush lasted for ~.4 seconds. The average RMS current is 15.3a during the inrush period.
    Once the system is stable the current at zero volume is 1.2A.

    [​IMG]


    Do you have a variac, current meter and a 1A fuse? If so put the fuse inline with the current meter and the output of the variac to the receiver. The variac may already have a fuse holder.

    Disconnect the +/- 80 V from the board and isolate the lines.

    Slowly ramp the variac and watch the current. I think you will be under 1 amp at all times. If all goes well the display should light up and the tuner should be functional.

    If that looks ok and the +/- 80 is not shorted to ground reconnect them and repeat the test. If you find that it looks basically normal as you ramp and the voltage gets close to 115 but the current is close to the limit of the fuse you may beed a bit larger fuse.

    This is basically how the Sencore instrument works when I test the boards. I set the current max for 1.4A then slowly raise the voltage and watch the current. I can usually see if there is a problem long before I get to the max current. If I do hit it the instrument cuts the power. To be fair the receiver is known good in this scenario and I am only looking for power supply issues related to assembly.

    Or you can use the DBT method. Or you could make a hybrid with your variac, dbt, current meter and a fuse holder.....

    I bet the original PS was just cooked. Once you get it going under stable power then you can sort out what ever else might be wrong with it.
     
  14. Cheddar Bob

    Cheddar Bob New Member

    Messages:
    6
    Location:
    BloNo, IL
    Thanks txturbo. My variac has a breaker on it but I'm not sure what the rating is, so I'll probably add the fuse. I think I'm going to going to take a look at the awf30 board any maybe a few others too. I was just a little freaked out to power up your pretty new board since some of my resistance readings were not matching the list.
     

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