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 Post subject: ZPA 0.5 control board problem
PostPosted: Sun Sep 08, 2019 6:19 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 96
Long time ago I bought this amp on a second hand site. It's a standard V2 version.The outside of this amp is like in new condition. Also the plexiglas is in top condition. This is what convinced me to buy this amp. I payed the top price for this amp. When the outside is in top condition after al these years the inside would be the same. Well... this time I couldn't be more wrong... . Inside this is the most fucked up amp I have ever seen or had. The guy changed the psu caps and the 2 little rail caps. One side of the power supply fet's where partly changed. Two fet's had burnt the board badly taken the pads with them. They removed the control board and messed up all throug holes. Several diodes were changed and also a transistor just underneath the fan connector on the left side. The SG3525 was also changed. Man, this amp was a mess. :cry:
Very disappointed I started the Restoration of this amp. The amount of work I spend already on this amp is unbelievable. Until now I have changed the 12 psu caps, the 16 fet's with the gate resistors and the 4 rail caps. I repaired all the 20 through holes of the control board (man this is hell to do). Changed the SG3525 and restored the bad solder work.

So after all this work I powered up the amp. I just powered it up few seconds to see if something bad happend and yes there was life!
Al the 4 red led's were powered up and also the 2 green lights. Man I was happy... yes yes now it is coming... the second time I powered it up. All the led's stayed of but the fans are working. The amp is dead now.

I took out the fan board and the control board. What slipped my first repair attempt is that the transistor Q21 was changed with another one than the original C2389. I started looking for a replacement but could not find a good one. So I asked the question on the forum and Jason (thank you man!) gave me a good replacement. The counter part (Q20) is also not replaced (it's still the A1035).
Other components that are smoked are: CR13 /CR14 on the fan board, CR21 CR22 / C23. R51 is cooked on the control board. What could have caused this?
I can change all these parts but I'm afraid that when I power the amp up again and the cause of this problem is not solved I can start over.

so please some advise of the experts....


Last edited by Silverhorse on Sun Sep 08, 2019 8:27 am, edited 3 times in total.

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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Sun Sep 08, 2019 6:25 am 
the Floor Sweeping Hack with Golden Ears

Joined: Fri Dec 19, 2008 9:53 pm
Posts: 14483
do you have the switch to tell if the plexi is in bypassed?



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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Sun Sep 08, 2019 6:31 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 96
hello Ttocs!

the switch is not in it's bypassed...


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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Sun Sep 08, 2019 6:42 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 96
some pictures when the amp just arrived...


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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Sun Sep 08, 2019 8:25 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 96
starting restoration...


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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Mon Sep 09, 2019 6:30 am 
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Joined: Sat Apr 19, 2008 11:57 pm
Posts: 1465
Location: Beaverton 48612
R29 and R32 burned most likely due to the main rectifiers being out of circuit and the amp being powered up. A lot of power gets dissipated across them if the main rails are down. They normally only see a potential of ~10V, with the main rails down they see about 70v.

CR13 and CR14 are there zener diodes which provide regulated +-15V rails. They typically run hot, but shouldn't burn. You might have an excessive load on your 15v supply. Also check their ballast resistors. R35 and R36, these power resistors get messed with when people try to "v2" the amps. If the ammo was powered with those resistors out of circuit, that could explain the zeners burning. Get rid of those idiotic oversized power resistors. Use the recommended v2 parts, not the biggest you can find. They will screw you being unsupported hanging off a vertical board. I don't know who started this trend, but it's insane. I have ti remove this crap from so many amps. Not only does it look terrible, but the joints will crack or the leads will break if the amp is actually used.

CR21, CR22, R51, and C23 are more troublesome. All are part of the O/L protection. My guess would be that one of the diodes failed shorted as is common, and took out the rest. Other than that there is potentially an issue in the poweramp or the circuit in the poweramp that triggers overload. This is one of the few PG amps which do not have all of the protection circuits opto-isolated. This means a fault can potentially drive full rail voltage into a circuit designed for much lower voltages. The LM339 on that card is there comparator that handles each protection circuit and HV/HC rail switching. I would expect there comparator to be damaged as well if that was the case.

The transistor you had to replace is partly responsible for the rail switching. I can't think of a plausible scenario for it to fail. I would check though that the high side rail isn't stuck in HV or HC mode.

I have cloned both the PS and fan control boards and put their schematics in the FB group. I'll try to post them here in a moment.

The only other thing I'd say is be careful with the eyelets, especially on higher density locations like there daughter cards. I personally do not like and will not use eyelets unless there is no other possible way to repair it. I've seen many failed installations because people lacked the proper tools or skills, and once you've drilled oversized holes in the board, you are pretty well committed. I'm nor saying you did a bad job, I've just seen a lot more failed attempts than successful ones and I don't want someone stumbling in this post whom had no clue what they are doing and attempt it.

I'll try to post schematics in a moment.

Later,
Jason



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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Mon Sep 09, 2019 6:40 am 
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I hope these work, I'm on my phone and could only find the pdf for one of them, the other is a screenshot.

I'm also not sure I'd they are my final revisions, but I'll try to get them from my PC when I'm back to the shop.


Attachments:
PS_Card_schematic.pdf [421.29 KiB]
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Last edited by Jacampb2 on Mon Sep 09, 2019 6:55 am, edited 1 time in total.
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M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Mon Sep 09, 2019 6:52 am 
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I found a screenshot for the final draft of my modified power supply card. The pdf attached in the last post may be more useful since the attached here has several deviations from the stock design including a switch to lock the amp in HV mode and buffers for the sg3525 to allow the amp to drive modern very high current power supply mosfets. Other than that, component designations should be consistent with the factory card even though the layout is fairly different to accommodate the changes.


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FB_IMG_1568040296395.jpg
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FB_IMG_1568040300903.jpg
FB_IMG_1568040300903.jpg [ 75.17 KiB | Viewed 163 times ]

_________________
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Mon Sep 09, 2019 11:00 pm 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 96
Hi Jason!

thank you so mush for this info. Now I can start finding the problem.
The vertical boards are original V2 versions, I don't know why the first owner replaced so much components, I guess he handled the trial and error route.
Do you have a link to the FB page? I did a search but cant' find it (I'm not a intensive FB user)


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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Tue Sep 10, 2019 2:30 pm 
the Floor Sweeping Hack with Golden Ears

Joined: Fri Dec 19, 2008 9:53 pm
Posts: 14483
https://www.facebook.com/groups/1473298426288964/



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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Tue Sep 10, 2019 3:55 pm 
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Here's a link to my general tech group on FB as well.

https://www.facebook.com/groups/149769529274064/



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M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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 Post subject: Re: ZPA 0.5 control board problem
PostPosted: Sun Sep 15, 2019 7:17 am 

Joined: Sat Aug 06, 2011 1:18 am
Posts: 96
ttocs wrote:
https://www.facebook.com/groups/1473298426288964/


Hi ttocs, I tried several times to become member of this group but it doesn't work. Status says "in treatment"


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