Phase 90 troubleshooting help

[solarplexus]

Hi,

I just got a Phase 90 today from my local store.  The owner wants me to repair it for him.  I looked at the pcb, looks clean everywhere, except the fact that the battery clip was cut off.  I replaced the battery clip but still doesn't work.  There is NO voltage from the input DC jack and NO voltage with a fresh 9v battery.  The jacks are plugged in, the adaptor is working, the battery is new, there is NO voltage to the input polarized cap or diodes whatsoever... or within the circuit whatsoever... could you give me any help ??

Thanks!

Matt

[tcobretti]

Did you check for volts where the + line connects to the board?  I'd start there and figure out where it stops.  If there's no power at the board, then the problem must be with the wiring.

BTW, tell that dude I'll give him $20 as is incl shipping.

[petemoore]

  Battery get hot ?
  Is there a short across V+/- ?
  Is V+ getting through the little resistor [isn't there a 100ohm between batt and circuit?] then to points on the board like Pins 8 of dual OA's?
  And ground, is ground getting to grounds and battery?
  and a Reverse polarity diode would work like a 1n4001, test that with meter .
 

[solarplexus]

the battery IS getting hot... I tried reversing the battery wires... nothing changed.

other than that... I really don't know what is going on...

could it be that one of the diodes at the dc input are fried ?  (even though they don't look fried) ?

[solarplexus]

BTW there is NO voltage reading at all from resistor to pin 8 of OA.

[solarplexus]

I also changed the dc input jack... nothing changed.

PLZ help!

[mdh]

A hot battery probably indicates a short between V+ and ground, as Pete suggested. Remove the battery, plug a cable into the input jack, and check for a short across the battery snap. If you see a short there, that's the first thing to fix. Look for solder bridges, possibly where the battery snap is soldered to the board, possibly elsewhere.

EDIT: to clarify, when I say plug a cable into the input jack, I mean a guitar cord in the effect input, *not* a power cable in the DC jack. This is just to be sure that the negative terminal of the battery snap is connected to ground when you test for the short. If the snap is shorted when there's no cable in the effect input, that's a clue that the problem is actually the battery snap itself, or where it's soldered to the board.

[petemoore]

  I'd do the close in light, mag glass if you got it inspection,
  Add no power during testing and only after V+/- are disconnected.
  Then I'd start opening things, like the DC jack circuit, cause it's probably easy to open/resolder, but first I'd check for grounds and what connects to what when [DC plug is in, testing where + and - actually go, DC plug is out...battery etc.].
  Then I'd pull a DC jack wire and test.
  Taking notes during the entire process of mapping the PS,DCswitch/jack/circuit/battery with unpowered DC plug in and removed.
  Ground short can be a process of discovery at best, then it becomes a process of elimination, the meter becomes useful again only after you lift something to test or something is changed, it can only say 'yes' or 'no' about connections.
   

[solarplexus]

thanks guys.... I checked everything I could.  checked with the magnifying glass, everything seems ok.  Changed the  battery clip, the DC input, still nothing will go in the circuit.  Every soldier looks good... damn... what else could it be?

[mdh]

Did you actually check (with a DMM) for a short, or otherwise low resistance between V+ and ground? If the battery is still getting hot, there is still a path of low resistance between V+ and ground, there's no way around that. It's certainly possible that you've wired the DC jack in such a way as to short V+ and ground, so it might be best to remove that from the circuit and try to get it running on battery power alone.

[solarplexus]

there is no way I could've wire the dc jack wrong, because it solders through the pcb, unless the pcb traces are shorted but they look clean, have not been tampered with...

The battery does not get hot anymore.

should I remove the dc jack ?

[mdh]

If the battery is no longer getting hot, then no, you should probably just leave the jack in there and move on to other avenues of troubleshooting. Start with the suggestions on the third line of petemoore's first post, or, of course, the instructions in the "What to do when it doesn't work" thread. If there still are no voltages to report anywhere past the battery clip, then you need to focus your efforts in that area. Sorry, we can't really debug this thing by remote control. You gotta follow your nose.

[e178453]

Fixed one of these with help from this forum a while back.  Suggest you replace the 5.1V zener even if it is not obviously bad, that is one problem I had.  The EVH model I fixed does not have series diode reverse voltage protection, it had a diode in parallel with the DC, which is not as good.  Had someone else been attempting to repair this before you got it?  That can be a bad thing.
scott

[Samy]

My bet goes to the zener and/or the diode right after the DC jack or battery clip. Check them with your DMM if they are OK but i bet that they wont ...

[solarplexus]

Thanks to everyone for your help...  I did learn new things and I think that my troubleshooting skills has improved with your help.

Diagnosis :  the input diodes weren't working.  Replaced them, everything works now.

Next time I have a pedal that doesn't light up, I change those first ! lol

Thanks again everyone!

Matt

[petemoore]

  Id, and test it first. Most all of these Si parts of a certain type will test like another known good one, that's nice  cause if you have another, you can see what a good diode reads on the meter display.