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    #21
    Re: Crest CPX1500

    took the crowbars out, plugged in and I still have short :S gonna check all diodes I can take out of circuit because many are zeners and are smd mounted.
    I did check a load of them but in circuit, and quite a few gave me readings backwards, but I didn't take much notice because it was in circuit, and none were shorted.

    I also noticed that on u200 I have 31.4ohms between vcc pins both ways...

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      #22
      Re: Crest CPX1500

      Originally posted by 5inc View Post
      ok, I took the regulators out, plugged in and no short. While I was reconnecting them i got a spark between 2legs of +15v regulator(I luckilly have a couple lying around so I just replaced it), from the main capacitors i guess.

      When I plug everything back on I still get the short. That's probably because I still haven't removed the bad zeners, so I'll get down to that now. I don't know if I should test it without anything in there. Should I?
      short appears to be on one or both of the 15v rails .

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        #23
        Re: Crest CPX1500

        Along with your other troubleshooting, which seems very agonizing to me, I see that the underside of the pcb shows about 50% of the connections are cratered. That means spending a little time resoldering. I would do that first.
        Is it plugged in?

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          #24
          Re: Crest CPX1500

          Thanks Longbow, will take your advise and get on to resoldering the board. After I search for the best way to do it with the tools I have.
          I apologize for my workflow, I studied carpentry, and no one ever tought me anything about electronics... that's why I joined this forum on the first place

          on the few free moments I had this week I gave with the short, it was on CR405/CR406.
          Went to the shop and got the zeners, and these fast diodes. They only had the 30v zener (CR321) in 1w, they told me it wouldn't matter, but being in a protection circuit (crowbar?) something tells me it might be a bad idea, am I wrong?

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            #25
            Re: Crest CPX1500

            Being rated for higher power (ie. higher current) won't matter in this case, as long as they're the same voltage
            Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

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              #26
              Re: Crest CPX1500

              Hi there!
              After a long break I decided to get back on this monster, have been fiddling around with it for a few days now, sorry for letting it cool down so long.

              What i've done this time is replace the shorted zeners, re-balled all connections nice and shiny(only the main board) and that gave me what seems like a good 30-0-30v line [by good I mean I tested that line alone, and fan spins + both GCL tm (protect) red leds stay on from the begginning, then (only) channel A green pwr LED comes on after a few secs, and nothing heats up excessivelly. NO short]
              Allthough I wonder why channel B pwr led won't turn on.

              I moved along assuming that was ok, and realized when i connect any of the 80v lines and fire it up first time fan turns on, my testbulb starts blinking a few seconds as if the short was intermittent(or something like that),leds blink along with bulb. Then everything dies, and bulb stays on bright, GCL protect led blinks randomly.
              After that when I switch it off and start it again it stays dead, fan goes around once and GCL leds still blink randomly.


              Starting to wonder if the power transistors I replaced in it's day are counterfeits.... or if there is a bad component that only acts bad when its in ON cycle.... I just can't find any more shorts with it unplugged on my DMM.

              does that ring any bell?
              Last edited by 5inc; 04-19-2017, 06:47 AM.

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                #27
                Re: Crest CPX1500

                Can you take some photos and re-upload them to the forum? The original links have gone dead
                "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                -David VanHorn

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                  #28
                  Re: Crest CPX1500

                  here are some pictures of the top and bottom of the main board, the diagnosis mentioned yesterday was for the other channel, that is fed by the red and yellow wires.
                  But this main board, that is fed by blue-black(80v line) and the orange-white has almost the same symptoms, when fired up a short blinks intermitently, pulsing 2-3times per second, and never stops. using a laser thermometer i checked if anything got excessivelly hot, but only mild warmth around q110 power transistor... about 23C' after a long minute blinking




















                  I didn't know where exactly to focus most so i just made a few generals, if there's anything precise you want to see just say..
                  thanks
                  Last edited by 5inc; 04-20-2017, 07:05 AM.

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                    #29
                    Re: Crest CPX1500

                    Thanks, but the photos are too small!

                    Please upload them to the forum in full size, as explained here: https://www.badcaps.net/forum/showthread.php?t=1868
                    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                    -David VanHorn

                    Comment


                      #30
                      Re: Crest CPX1500

                      Sorry about that, here are the best pictures i could take, the two last ones show closeups on tiny ceramic caps that read low resistance:
                      c202(32,8ohm)
                      c207(4,3)
                      c102(100)
                      c107(73)

                      I also have low resistance through diodes:
                      cr100(140ohm)
                      cr101(114)
                      cr200(85,5)
                      cr201(57,3)

                      Hope it's something...
                      Attached Files

                      Comment


                        #31
                        Re: Crest CPX1500

                        Those caps are smd mount, so I rather not take them out untill I'm clear about them, the schematic states they are surface mount capacitors, value (0.1) so the only reference I have is the size (0805) and this value 0.1

                        I 'm guessing it's nF, by the fact that the only other values in the scheme written on caps are uF and pF, but i'm not sure...



                        thanks

                        Comment


                          #32
                          Re: Crest CPX1500

                          Ceramic capacitors listed 0.1 are most likely 0.1uF which is 100nF

                          What I am interested in is what seems to be a blown component near a heatsink? Which part is that? I can't read the silkscreen.

                          Which LED blinks? CR307\CR301 "DDT LED"?
                          Attached Files
                          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                          -David VanHorn

                          Comment


                            #33
                            Re: Crest CPX1500

                            Originally posted by 5inc View Post
                            Sorry about that, here are the best pictures i could take, the two last ones show closeups on tiny ceramic caps that read low resistance:
                            c202(32,8ohm)
                            c207(4,3)
                            c102(100)
                            c107(73)
                            I assume you have probed each capacitor in both directions with your meter to ensure you are not measuring a forward voltage drop or such?

                            You may still have some short on the 15v rail(s) somewhere.

                            For example, C202 and C102 are in parallel with each other and also in parallel with CR115 and CR215 - via R121\R221 and R194\R294 at point 15+PA.

                            If CR115 or CR215 was bad, you would read a low resistance across C102 as well.
                            What resistance do you get if you measure directly across those diodes?

                            Also check CR224 and CR124.

                            Originally posted by 5inc View Post
                            I also have low resistance through diodes:
                            cr100(140ohm)
                            cr101(114)
                            cr200(85,5)
                            cr201(57,3)
                            What exactly do you mean by 'low resistance through diodes' ? Directly across the diodes themselves? Or from the diodes to some other point such as GND?
                            Last edited by Agent24; 04-24-2017, 08:25 PM.
                            "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                            -David VanHorn

                            Comment


                              #34
                              Re: Crest CPX1500

                              Thanks for your reply Agent24!
                              Yes that is a 220ohm resistor (r338) that had become toast, I replaced it for a salvaged one, and it has a little extension in a leg, that is what looks funny. I'll give the heatsink a scrub to get the stain off.
                              Then, both DDT(cr301,cr307) leds shine but also pulse brighter along with one signal led(CR302).
                              At the same time, power led (cr306) lights up on and off (unlike the before stated,by the fact these go completely on and off, whilst the others don't go off totally), at the same rythm as the others.
                              Finally, I think every 7 times all these blink, power led cr300 blinks once. the 7pulses happen in about 2seconds.


                              Now, about the caps, my DMM beeps whenever it reads a low resistance in diode mode, I believe around 100ohms or less, and also shows a value that I don't know if it is voltage drop, resistance, or what (the fact is good diodes read around 600-800 in one direction, 1800 or OD in the other.
                              I then probe a 4,7ohm resistor and it reads 003, and a 47ohm resistor reads 45... I imagine it will be voltage drop but not sure)

                              So in diode mode, I probed c202 both ways, and get a reading that says 30 (I then probed in ohm scale and read 32.8ohms)
                              I then go to the other side and probe c102 and read 100 in diode mode, and 98 in ohm mode.

                              c107 reads 72 on diode mode, 73.8 in ohm scale
                              c207 reads 97 on diode mode, 98.8 in ohm scale

                              CR100 reads 140 on diode mode both directions
                              CR201 reads 114 on diode mode both directions
                              CR200 reads 84 on diode mode, both directions
                              CR201 reads 56 on diode mode, both directions

                              Now I probed CR115 in diode mode and read 948 in one direction and 1616 in the other, in ohm scale it reads different in each scale
                              CR215 and read 740 in one direction, 1202 in the other. in ohms it reads around 4.5kohms and growing slowly.

                              CR124 reads 733 in one way and OD in the other
                              CR224 reads 725 one way and about 1780 in the other.

                              And when I say "low resistance through diodes" I mean directly across the diode itself (in circuit)...
                              I hope that was helpfull, I'm kind of confused right now.

                              I also have this doubt, in the schematic R221 is connected to what i believe is earth and ground, is that so? if so which is which?

                              Thanks!

                              Comment


                                #35
                                Re: Crest CPX1500

                                Since you had CR321 short and burn up R338, I am suspicious that U303 may have been damaged at the same time CR321 was.

                                It is part of the fan controller and over-temperature shutdown, and overrides the power-up delay signal from U300 if this happens.

                                I wonder if a fault in U303 is shutting down U300 repeatedly, and that is why the power LED blinks...

                                Can you show a close-up of U303? It seems to have a mark on it, I don't know if it's a burn mark or flux.


                                With R221 it's connected between earth ground and chassis ground. But I am not sure they have used the symbols consistently through the entire schematic. I don't think you need to worry about it at the moment. Unless one side is not connected when the PCB is not inside the case, which could cause problems.

                                Symbols are here: https://en.wikipedia.org/wiki/Ground...y)#Electronics
                                "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                -David VanHorn

                                Comment


                                  #36
                                  Re: Crest CPX1500

                                  The stain on U303 was flux, but i went down to the city this morning to get other stuff and got me 4 pieces of these just in case. And thanks to that I checked again & found a dead short between pins 2 and 8, that doesn't seem to be there in the schematic, will proceed to replace it and hope that solves the problem.

                                  Thanks again

                                  Comment


                                    #37
                                    Re: Crest CPX1500

                                    Originally posted by Agent24 View Post
                                    With R221 it's connected between earth ground and chassis ground. But I am not sure they have used the symbols consistently through the entire schematic. I don't think you need to worry about it at the moment. Unless one side is not connected when the PCB is not inside the case, which could cause problems.
                                    /wiki/Ground_(electricity)#Electronics[/url]
                                    I don't quite understand when you say "Unless one side is not connected when the PCB is not inside the case, which could cause problems". I DO have one side disconnected, I have the 6 red/yellow/black/red/green/black leads that power up the channel in the smaller board... (since both channels gave trouble i thought it might be wise to fix one then the other...)

                                    I just took out U303 and saw there is a line on the board from pins 2 to 8, so not a short. Replaced it for one of these I bought this morning, but it still acts the same.



                                    .....And what about the caps... shall I also replace them?

                                    Comment


                                      #38
                                      Re: Crest CPX1500

                                      check the small transistors that feed the base pin of the power transistors.

                                      i have seen people replace shorted power transistors before, without realising that the power transistors damaged the smaller transistors driving them.

                                      the result is the small transistors turn the new power transistors full-on causing an overload or blowing stuff again!

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                                        #39
                                        Re: Crest CPX1500

                                        I took out q106(mje15032) and tested on diode mode all combinations

                                        positive, negative reading
                                        collector-emitter od
                                        collector-base od
                                        emitter -collector od
                                        base -collector 573
                                        base -emitter 574
                                        emitter -base od


                                        And q107(mje15033) read

                                        collector-emitter od
                                        collector-base 596
                                        emitter -collector od
                                        base -collector od
                                        base -emitter od
                                        emitter -base 596

                                        Q102 (8050) read

                                        collector-emitter od
                                        collector-base od
                                        emitter -collector od
                                        base -collector 716
                                        base -emitter 716
                                        emitter -base od

                                        Q103 (8550) read
                                        collector-emitter od
                                        collector-base 690
                                        emitter -collector od
                                        base -collector od
                                        base -emitter od
                                        emitter -base 690

                                        Sorry I wrote the whole table, wasn't sure base was the significant pin. But appart from that, they look fine don't they?

                                        I still think about those tiny ceramic caps, do you think I could replace those for some small 104's?

                                        thanks!

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                                          #40
                                          Re: Crest CPX1500

                                          I also took out q104&q105(1837 & 4793) and they both read fine aswell...

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