Peavey XR-700 Powered Mixer (tech info for repair)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Bee, May 22, 2015.

  1. Bee

    Bee Member

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    Ok boys, I have a Peavey XR-700 on my bench for repair. I can't find any schematics for the power supply etc. The only schematic I have found is for the preamp board(no voltages), which is not of much help cause I need to trouble shoot the power supply.

    If anyone has information, links to, or schematics they would like to share, I would be ever so grateful.

    Also if someone has this mixer and can take a few voltage measurements of the power transformer secondary AC voltage, that would be of great help, cause then I could calculated my way through the power supply if I know what the transformer is supposed to be putting out.

    This is old analog beast with spring reverb needs a second chance otherwise I will be parting it out.

    Thanks!

    Here is a picture (from google images) of the mixer for reference.

    http://www.bakerproav.com/images/peavey_xr700.jpg
     
  2. Bee

    Bee Member

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    Nice, Kyle!

    Thanks. So, +15/-15 +15/-15 both center tapped secondaries looks like. I don't understand why they don't show the Power Transformer in Schematic, ever seen the P.T. Schematic?

    P.S. Send the bill to my Wife! :anon
     
  3. Bee

    Bee Member

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    I'm not sure this is complete with the power supply, cause my unit has a 5000uf/75v main input supply cap and I can't find it on this schem. Hmm maybe someone was in this before? Either way this cap is leaking badly.

    If you come across anything else, let me know. Thanks for your time!
     
  4. Kyle B

    Kyle B Supporting Member

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    The schematics might quite possibly be missing "the power supply". But you have like 98% of the circuitry covered between those two schematics.

    It should be a relatively simple task to trace-out the remaining stuff. The power supply in that bad boy isn't likely to be anything exotic. Just a bridge rectifier, a monster-sized capacitor, and maybe a power resistor or two and probably some sort of thermal cut-off (likely located in the power transistors heatsink).

    Or try calling Peavey - They are really exceedingly helpful in tracking down old schematics!

    If the cap is leaking, obviously it needs replacing. Heck, that might be enough to get it working again! The chance of a bad power transformer is very very small really. Of anything in there that's not likely to fail, the PT would be near the top of the list.

    Insofar as how much voltage the transformer should be putting out... You can figure it'll be something significantly less than 75V! (Because that's the rating on the bad cap) You can even estimate the voltage by taking the rated output power in the rated load, then apply ohms law (P=V^2/R ... rearranges to SQRT(P*R)=V)
     
  5. Bee

    Bee Member

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    Thanks again Kyle.

    Great advice. I'm going to test and replace any bad caps in the power supply and then see where I'm at from there. Those damn 5000uf caps aren't cheap! I can't complain, I bought this mixer for $20.

    Most my experience has been with hand wired tube gear, so this is a good learning experience for me. I'm not a seasoned tech, but have learned enough to know I have more to learn. I greatly appreciate the info and time supplied by guys like you who have lots of experience and knowledge. I started servicing my guitar tube amps about 2 years ago with the plans to become self sufficient and avoid bench fees(goal accomplished). I have fell in love with this work and it's my passion now. I have a few repairs and custom builds under my belt. At this point I want to learn and work hands on as much as I can, and would like to start a small business on the side doing repairs and custom builds...to fund more projects! End of rant.

    P.S. I understand and practice all safety procedures EVERY time I perform any work or tests.
     
  6. mark norwine

    mark norwine Member

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    What exactly is wrong with it?
     
  7. Bee

    Bee Member

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    I bought this mixer as is, the guy said it would not turn on. Basically dead. I turned in on with my current limiter and a variac. No Shorts. But it will not pass audio (had an ipod plugged into it). The is a steady hum at the speaker output. So I turned it off and tested the Main input cap which is badly leaking. I didn't properly spend much time with troubleshooting yet. So I stopped there. Although I did notice I wasn't getting any voltage on filter cap following the Bridge Rectifier. There was voltage on the Bridge Rectifier diodes though.

    I will spend more time on this with more methodical troubleshooting rather than random test like I've done so far, now that I have the schematic.

    Also, none of the LED indicators turn on.

    Thanks for your time, I will do as instructed if you are willing to proceed with helping.
     
  8. mark norwine

    mark norwine Member

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    It sounds like it's in your B+ rail.

    Start at the source & work logically. You'll find it.

    Wait...back up...you *bought* (as in money?) a non-working '80s era Peavey 7-channel (!) powered mixer?
     
    Last edited: May 22, 2015
  9. Bee

    Bee Member

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    I tested the P.T. with no load on it. With 100vac on the primary = 2.6vac on the secondays Which seems really low? Maybe I don't understand this circuit or I'm just used to high voltages of tube gear.
     
  10. mark norwine

    mark norwine Member

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    2.6Vac is way too low.

    Was the secondary disconnected from all down-line components when you made that measurement?

    If yes, your PT sounds fried.

    If no, it could be a shorted component (diode) that's drawing a $hitload of current, which is sinking your voltage.

    It's almost impossible to troubleshoot components....especially transformers....while they're still wired into the circuit.
     
  11. Bee

    Bee Member

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    yeah, the transformer was completely disconnect from the circuit. My variac on the primary and meter on the secondary.

    I paid $20 for it. I'm just looking for gear to repair for educational purposes. I want to determine if the P.T. is toast cause there is no point in recapping etc. if that is the case...
     
  12. mark norwine

    mark norwine Member

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    if you're certain that you are applying the voltage to the right wires, then.....yeah.....sounds fried.

    Remove all power & measure DC resistance on the windings. My guess is that one of them (and I'm betting it's the sec) is burned open
     
  13. Bee

    Bee Member

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    Could it be partial open on the primary...cause there is still a small amount of voltage on the secondary and when hooked up to the circuit it does try to charge up the input cap.
     
  14. Bee

    Bee Member

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    I did measure dc resistance and the resistance was low enough to activate my continuity alert on the meter. I don't remember exactly the ohms but less than 1k range. I can check exactly what it is if you give me a minute.
     
  15. Bee

    Bee Member

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    Just re measured the dc resistance.

    Primary: blue(primary) to black(primary) = 2ohms


    Secondary:

    Orange to Orange/White(center tap) = 3.9ohms
    Orange to Orange/White(center tap) = 3.9ohms
    Orange to Orange = 6.6ohms

    Red to Red/White(center tap) = 1.4ohms
    Red to Red/White(center tap) = 1.4ohms
    Red to Red = 1.4ohms

    There is no continuity between the separate windings.

    Now that I type this out it looks like the Orange-Orange/White-Orange Secondary is the problem?
     
  16. mark norwine

    mark norwine Member

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    in an earlier post, you said that "the secondary [singular] was 2.6 vac".....but you now say that there's multiple secondaries. We're going to get nowhere with incomplete / partial information.

    Put 120 in the pri & make no-load ac voltage measurements of all windings. If you can, monitor the pri current as well.

    Report back
     
    Last edited: May 22, 2015
  17. J M Fahey

    J M Fahey Member

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    Agree and add:
    1) build a lamp bulb limiter http://www.ssguitar.com/index.php?topic=2093.0
    A 60W or 75W lamp will be fine.
    A real filament one of course, either the old type or the new semi high efficiency ones which have a small filament and transparent bulb inside a larger conventional glass one, not CFL or LED lamps.

    2) you will get somewhat less than 120V on primary, measure voltages in the center tapped windings you found.

    I'd expect around 15+15VAC on the low power (preamp) ones (Or , Or+Wh , Or) and around 35+35VAC on the high power (main amp) ones (R , R+W , R) so some 30VAC and 70VAC end to end respectively.

    Limiter lamp glowing red or dull orange= fine
    Bright orange/yellow/white= different degrees of trouble.

    Post results.
     
  18. Bee

    Bee Member

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    Sorry for the delay. I was away this weekend. (I don't have a smart phone, yeah really, so I can only access the internet at home)

    Anyways.. I will have some time today and this week in the evening after work to get back on this. I will report back with COMPLETE information and correct the false results I posted about the Transformer originally.

    I sent an email to Peavey before I started this thread asking for the schematics. They just got back to me and with the FULL set of schematics and PCB board/component layouts! Those guys are great! The transformer schematic is in there too. I re tested the transformer unloaded and loaded and can confirm it is in normal working order matching the schematic.

    I have do have a dim bulb limiter set up in series with my variac and have been using when powering the mixer up. No immediate shorts were presented so far.

    Like I said I will have to report back with details. I don't want to send you guys a wild goose chase anymore than I have already. And I apologize for the incomplete info so far.

    *I have a blown fuse on the OR-OR/WHT-OR secondary(this fuse is in series with the secondary to the 'power board'). I will have to find a replacement for it. Buss MDV1 250v axial

    There is a second fuse on the Red secondary that I could borrow for testing I suppose (with the Red secondary disconnected)

    Thanks!

    P.S. I will post all the schematics and board layouts for reference. Just got to figure it out real quick.
     
  19. Bee

    Bee Member

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    J M Fahey likes this.

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