Zpa0.5 repair issues/questions

[vwdude]

I will first fill in those who haven't seen.the previous thread. I bought a zpa for a good price but it was dead. It was previously "repaired" by a person with really bad soldering skills. I replaced all power supply caps(8200uf 16v 105*c). I replaced all power supply FETs with irfz48n and all of their resistors with 330 ohm 1% resistors.

When powered up I have a short. I replaced all FETs again yesterday and found a lead from a resistor that was not stuck to the board anymore and was not connected to the FET. I fixed that. Now it shorts before I even power the remote turn on.

So when I test the ground pin to the center pin I get continuity and when I test the other pin (connected to the resistor) it does not have continuity with the other 2. That doesn't seem right. I always assumed that the bus bars were powered and the board had that gold layer for ground.

Are the caps causing the apparent short? I get 63.4 k ohms across each cap. When I measure the resistance between the ground pin and center pin on the FETs some are 63k ohms and other go either up or down without an end. Does it seem like I have a short? It could be something else going on but I don't see anything else that looks bad.

Thanks for any help. If I can't fix this I might just sell it as is. Cosmetically it's in great shape I just have something strange happening here.

[trickyricky]

Man that sucks that you had to replace the fets twice and still no luck. I remember working on my ti500.4 and my dumb ass left it on without a heatsink or fan (yeah now I know, lol) and I blew out a channel's outputs, was lucky that was all the damage that was done.

When describing which pin is which it would be better off stating "base/collector/emitter/gate" rather than center pin or ground pin. That way we know exactly which pin your referring too. Maybe its just me.

[vwdude]

Thanks for the update. i didnt use the base, collector, emitter, or gate because I thought people would be more familiar with which pin it is.

So an update, ive been working with someone that has worked on a bunch of these. His suggestion was to remove the FETs and see if the short went away. Removed all FETs and theres still a short, but the ohm load went from 2.2 ohms to 160k ohms. A better way to describe the short is across all caps and collector/emitter pins I had a short.

It looks to me that I got rid of the short by removing all FETs, can anyone confirm or deny this? 160k ohms seems to be pretty close to open circuit. If this is the case I will reinstall the FETs one at a time and check the ohm load. Caps seem not to be an issue.

[zeropoint0.5]

I suggest you check the board before you place the fet's back in.....it Always could be a short cause of a little bid of solder connecting two pins.....

measure the board and traces out first for conductivity/no shorts......

Using the irfz48 and 330ohm resistors should be fine..... i have 3 or 4 zpa's 0.5 already with them in......

good luck.....

if you can't fix it yourself, i suggest you contact Eric D or Valeks before you mess up the amp........

[vwdude]

I removed all FETs and the short went away. I now have 1 FET per transformer and no short. I am ordering all new FETs again, and I will install them 1 at a time and verify that there is no short.

[trickyricky]

Check them before soldering them, one of them could of been a defective one (rare but possible). Time consuming but it will safe you lots of money.

[valeks1]

When powered up I have a short.

How do you know you have short? Amp draws lots off current?

[valeks1]

Because you use different MOSFETS you probable need to adjust GATE resistors.

[vwdude]

I know I had a short because the center pin (power) on the MOSFETS and the grounding pin read 2.2 ohms.

The gate resistors were changed with the new MOSFETs to the 330 ohm (IIRC) from the 33 ohms that it had.

So when I powered it up before, it would short before even connecting the remote wire. Now, i can have power and ground connected and its fine, but when I connect the remote it shorts. I am looking further down the line now for a short. I think this is going back to the amps initial problem, which must have been deeper than i originally thought.

I have always put all new MOSFETS in during this diagnostics...i will not reuse MOSFETs as I cant afford to troubleshoot with potentially bad MOSFETs.

The guy who sold me the amp said that one MOSFET was burned, and he had some guy replace it. When I got the amp, the power supply caps had leaked everywhere and I found bad soldering by the replaced MOSFET plus another totally burned one. I also found about 2 or 3 others that had slight burn marks under them. Thats why I replaced all MOSFETs, gate resistors, and power supply caps. Now it looks like there might be some bad stuff on the output side. I will check for fluid under the other caps, and see if i find any shorts in other transistors.

When all is said and done, I would love to use this amp to run my 12" Xmax off of. My McIntosh amp does not run a sub very well on channels 5 and 6. This way I can go active with my front 3 ways.

[zeropoint0.5]

I know I had a short because the center pin (power) on the MOSFETS and the grounding pin read 2.2 ohms.

The gate resistors were changed with the new MOSFETs to the 330 ohm (IIRC) from the 33 ohms that it had.

So when I powered it up before, it would short before even connecting the remote wire. Now, i can have power and ground connected and its fine, but when I connect the remote it shorts. I am looking further down the line now for a short. I think this is going back to the amps initial problem, which must have been deeper than i originally thought.

I have always put all new MOSFETS in during this diagnostics...i will not reuse MOSFETs as I cant afford to troubleshoot with potentially bad MOSFETs.

The guy who sold me the amp said that one MOSFET was burned, and he had some guy replace it. When I got the amp, the power supply caps had leaked everywhere and I found bad soldering by the replaced MOSFET plus another totally burned one. I also found about 2 or 3 others that had slight burn marks under them. Thats why I replaced all MOSFETs, gate resistors, and power supply caps. Now it looks like there might be some bad stuff on the output side. I will check for fluid under the other caps, and see if i find any shorts in other transistors.

When all is said and done, I would love to use this amp to run my 12" Xmax off of. My McIntosh amp does not run a sub very well on channels 5 and 6. This way I can go active with my front 3 ways.

Last week i replaced myself a total powersupply in a zpa0.5....there was one P55N06 fet burned, so next to the 12ps caps, i took out all 16 P55N06 and

16 33ohm gate resistors out to replace them with 16 irfz48 and 16 330ohm gate resistors and it works just fine !!!!!!

So probably something went wrong somewhere in you're work..... But diff to help from distance......

Valeks responded here to you.....why don't you send the amp to him for a total checkup/repair and upgrade to V2 if it's a V1......

would be better cause i'm guessing with al the solder/desolder jobs you are doing, you're will end with a messed up board.......

[vwdude]

I hear you. I am trying so e quick troubleshooting stuff before I give up. I suspect it's something beyond the power supply that is bad. I removed the rectifiers and will try it again. I suspect something further in the system as I know there's no short with the caps, and I'm down to 1 fet per transformer and it still shorts on 2 of the transformers. I will recheck the 330 ohm resistors as well to make sure there's nothing funny there.

I am determined to get this working. Changing caps, fets and resistors is simple for me. I did it for 8 years in college and for many years since in my job. The challenge, as many have said, is when someone was in there before me, mucking around and messing with stuff.

I almost wonder if the rectifiers are an issue. Either way, I will post up my results with testing after removing the rectifiers.

[trickyricky]

Zeropoint, I was told that the 33ohm would work with the IRFZ48's.

Am currently working on one, the power supply section. I already have the IRFZ48 and some fuse 330ohm resistors....are you sure you had 330ohm and not 33ohm? Maybe a pic of the actual board with the 330ohm resistors will convince me (not that you have to).

[zeropoint0.5]

Zeropoint, I was told that the 33ohm would work with the IRFZ48's.

Am currently working on one, the power supply section. I already have the IRFZ48 and some fuse 330ohm resistors....are you sure you had 330ohm and not 33ohm? Maybe a pic of the actual board with the 330ohm resistors will convince me (not that you have to).

the first time i putted the irfz48 in a zpaV2, i didn't know with some fet's they used 33 ohm gates, cause i based myself on the shematic.......

what happened was, directly after powering up, 3 of the 33 ohm resistor burned immediatly and the 3 irfz48 fets connected to it were blown also,

so i had to replace those 3 irfz48, and also the 16 33ohm gates to 330ohm gates......

http://www.newark.com/international-rec ... ch=Popular Products

http://www.newark.com/multicomp/mcmf0w4 ... ch=Popular Resistors

no, for 100% sure, with the irfz48 you need 330ohm gates, exactly as with the irfz44 who are in some V1 models.....

[zeropoint0.5]

with NDP7060 and STP55N06, mostly in the V2's, there are 33 ohm gate's in.....

with irfz44 and irfz48, Always 330ohm gate resistors..... in the zpa0.5................

[zeropoint0.5]

i have some pics but it is a bitch everytime to resize them....

send me you're emailadress in pm and i'll send you the pics by mail.......

[vwdude]

the person that is giving me advise on repairing this amp says that with the irfz48 I should use 47 ohm resistors. He has restored dozens of these amps. He thinks that my issues are due to the 330 ohm resistors.

[zeropoint0.5]

the person that is giving me advise on repairing this amp says that with the irfz48 I should use 47 ohm resistors. He has restored dozens of these amps. He thinks that my issues are due to the 330 ohm resistors.

i have done 5 or 6 zpa0.5's with irfz48 and 330 ohm gate resistors and they work as fine as they can be..... never ever the powersupply even

starts to get hot.....

My best guess now is, the moment you stop listening to that person will probably the day you're zpa0.5 will play again......

anyway, good luck........................

[Eric D]

If you have a short in the transformer, you can end up burning up good FETs instantly. If they keep failing on the same side of the amp, but not on the other, then I would guess there is a good chance you have a problem with the transformer.

[trickyricky]

Well I went with the more robust IRF3205's and the 33ohm gate resistors (fusible/flameproof) and powered mine up, I quickly notice the amp was pulling 10amp (fuse pop and my light bulb was bright) it also dropped my power supply voltage down to 3.5dcv. So I took it apart and went oven all my solder joints, all was good no solder bridges. Then I notice a trace was open and that was my issue. Solder a jumper wire and powered it up again with fuse and light bulb...this time the puppy had all four red LED's on and both green LED's on the vertical boards lite.

Now time to adjust the bias and dc offset as someone clearly has messed with them. My very good friend suggested I replace those dc off set pots with ten-turn pots....might consider doing just that.


VWdude....I would check very closely the small traces that go to the vertical board as that's where mine was. Now I didn't blow up or damage any of my fets or gate resistors when I powered it up and it was pulling excessive current, so if yours is damaging the fets you might have other issues.

[vwdude]

Well I went with the more robust IRF3205's and the 33ohm gate resistors (fusible/flameproof) and powered mine up, I quickly notice the amp was pulling 10amp (fuse pop and my light bulb was bright) it also dropped my power supply voltage down to 3.5dcv. So I took it apart and went oven all my solder joints, all was good no solder bridges. Then I notice a trace was open and that was my issue. Solder a jumper wire and powered it up again with fuse and light bulb...this time the puppy had all four red LED's on and both green LED's on the vertical boards lite.

Now time to adjust the bias and dc offset as someone clearly has messed with them. My very good friend suggested I replace those dc off set pots with ten-turn pots....might consider doing just that.


VWdude....I would check very closely the small traces that go to the vertical board as that's where mine was. Now I didn't blow up or damage any of my fets or gate resistors when I powered it up and it was pulling excessive current, so if yours is damaging the fets you might have other issues.

Thanks, I will take a look. I have been super busy and haven't had a chance to try anything. I did discovered that 2 or my "330 ohm resistors" were readin just over 100 on my dmm. I will order more resistors and FETs. Is there a better choice than the 48?

Btw the person that has been giving me advise (only recently) is Shawn k. I've seen his work he seems to know his stuff. So far the only thing I have down tht he advised me to do is to remove the rectifiers to see if the short is with the power supply or past the power supply. Like I said, been too busy to do much the last few weeks.

[zeropoint0.5]

Well I went with the more robust IRF3205's and the 33ohm gate resistors (fusible/flameproof) and powered mine up, I quickly notice the amp was pulling 10amp (fuse pop and my light bulb was bright) it also dropped my power supply voltage down to 3.5dcv. So I took it apart and went oven all my solder joints, all was good no solder bridges. Then I notice a trace was open and that was my issue. Solder a jumper wire and powered it up again with fuse and light bulb...this time the puppy had all four red LED's on and both green LED's on the vertical boards lite.

Now time to adjust the bias and dc offset as someone clearly has messed with them. My very good friend suggested I replace those dc off set pots with ten-turn pots....might consider doing just that.


VWdude....I would check very closely the small traces that go to the vertical board as that's where mine was. Now I didn't blow up or damage any of my fets or gate resistors when I powered it up and it was pulling excessive current, so if yours is damaging the fets you might have other issues.

Btw the person that has been giving me advise (only recently) is Shawn k. I've seen his work he seems to know his stuff.

I apoligize for my last words.....

I just did yet another zpa0.5 last night replacing the P55N06 and 33 gate resistors with irfz48 and 330 ohm gate resistors and again it plays

as fine as it can be !!!!!! Every post is to help you solving the problem......I understand very good the frustration of not getting an amp back

good . the only positive thing of it is, you learn...you learn how to search and solve the problem...... I hope you find it soon