Zx350 OVL then Steady Green after cap repair

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GettinOlder
Posts: 7
Joined: Tue Mar 30, 2021 4:06 am

Zx350 OVL then Steady Green after cap repair

Post by GettinOlder »

Ok, so I replaced the power caps and rail caps. I think everything went well but I energized the amp and the the OVL turns on for a second, the fan stops and then powers up again and get the green light. It stays lit and fan runs. This is with no speaker connected. So I then connected a speaker on one channel (left) and no sound. (Only tested this channel). I adjusted the gain pot and no sound (per say) but get static as I change the gain. The static sound pops here and there and does increase in volume as I increase gain. If I turn the gain all the way up, it turns off!? I’m using a little 12V power supply to test (didn’t want to use a battery or the car itself in case if blew up!). Should I use a proper 12V source (battery)? But checked the voltage at the rail caps and found 38.7 Vdc each cap. Any ideas?? Where I can start testing this Zx350v1 by the way. Thanks!!
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Jacampb2
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Joined: Sat Apr 19, 2008 11:57 pm
Location: Beaverton 48612

Re: Zx350 OVL then Steady Green after cap repair

Post by Jacampb2 »

Overload led for a few seconds and then green led is normal startup behavior. The o/l led is lit while the poweramp is muted during power up. This is to keep any pops or thumps from hitting the speakers.

The amp can easily overload a small DC power supply. You can run a more stout supply and either a 2R current limiting resistor or a serious 12v headlight bulb and it will save your bacon if there is an issue.

Why there is no audio, well, if you pulled the rail caps, I'd bet money on board damage. If you compromised the through hole plating both rails will not be present everywhere they are needed.

Other than that, the ribbon cables are common failure points as are the configuration switches. Double and triple check that the crossover is configured correctly.
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
GettinOlder
Posts: 7
Joined: Tue Mar 30, 2021 4:06 am

Re: Zx350 OVL then Steady Green after cap repair

Post by GettinOlder »

So I have been doing a lot on this amp and keep finding little issues. I have also visited another forum on fb and learning a lot. So far I have pulled both bass boost and gain pots, opened them up, cleaned them up with deoxit and made major improvements. Then ended up breaking the ribbon cable solder joints on the daughter board and ended up replacing with wires instead. Also, I pulled the fan, heatsinks, isolation plates and removed the old compound on the chips and replaced it with dowsil 340. Now all my channels have music and no static, thumps or pops while sweeping the gain. But my left channel is clean and performs well, my right channel seems to have some distortion. I bypassed the daughter board as a test and connected the mainboard XVR interconnect pin 8 (right channel signal) and pin 2 for shield to my rca input and made a huge improvement so I will remove my daughter board completely and put individual RCA jacks Jason recommended (his knows his stuff and boggles my mind!). I get a little thump while shutting down the amp still so I'll now checking my fusible resistors and see if any of them are open. The saga continues! Once I get this project over (I can feel it in my bones that the end is near) I'll post some progress pics and part #'s so I can help the phorum community in case someone else needs help. Stay safe.
GettinOlder
Posts: 7
Joined: Tue Mar 30, 2021 4:06 am

Re: Zx350 OVL then Steady Green after cap repair

Post by GettinOlder »

So all is good in the world now. Finally. With the help of Jason and my numerous questions (and he answered everyone!). So my amp had a few bad resistors in the right channel. No blown drivers but one fused resistors was shot and another couple burned to a crisp. I replaced them and my amp is better than new. The sound is awesome! I had a it run for an hour on my test bench driving to a pair 6x9’s (moderate volume) and no issues.

I ended up replacing the power caps, rail caps, some of the smaller caps with nichicon MUSE caps, removed the xover board, new fan, changed the 2W resistor for the fan to 1W and re-pasted under the heatsink. Hopefully it runs nicely for the next 20 years!
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Jacampb2
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Posts: 1562
Joined: Sat Apr 19, 2008 11:57 pm
Location: Beaverton 48612

Re: Zx350 OVL then Steady Green after cap repair

Post by Jacampb2 »

You will be very happy with it. Enjoy it and then pass it on to your kids. Build your own little phoenix phamily!
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
GettinOlder
Posts: 7
Joined: Tue Mar 30, 2021 4:06 am

Re: Zx350 OVL then Steady Green after cap repair

Post by GettinOlder »

Some of what is written below was mentioned in previous posts above but I decided to start from scratch. The last few months have been a blur so I'm going through the process I went through as I write it.

So, after many testing and determination, this ZX350v1 has a new life! I purchased this amp online and did not think I would end up rebuilding this amp except the dreadful leak on the power caps. The amp case was a 8 out of 10 cosmetically and the previous owner said it was wrapped up in a plastic bag for 20 years. He said it was working fine when he put it away years ago (obviously not), but he had no problems sending me pictures of the couple of scratches (minor blemishes for a 20+ yr. old amp) and even took off the cover to take pictures of the guts. He couldn’t find the plexi windows either. (in can you don’t know, these first versions of the ZX series amps were not bolted to the case but glued instead and many of the windows have fell off due to the adhesive losing strength from heat itself imagine). I decided to purchase the amp (it was a very attractive price after negotiating!) and hopefully revive this amp.
I did not power up the amp when I received. I took the cover off, pulled off the daughter board (xover) and noticed the rail caps. Two of them were bulged and I was going to replace the power caps anyways, I decided to replace the rail caps too. Except some dust bunnies, the PCB looked good. So, I ordered the caps. When they came, I replaced the caps with higher values like most do. Nichicon caps as well. Two of the power caps were in fact leaking and I cleaned the board and replaced all the caps. I couldn’t wait to hear the amp! Once I hooked it up, it came to life! But no sound… I was upset. I started to play with the gain and bass boost pots and awful scratchy, popping sound were coming out of my test speakers! After researching this forum, this happens and because the pots are obsolete, I decided to rebuild the pots following the sticky in this phorum. Cleaned it up, deoxit, tested with DMM and soldered them back on the board. Time to test again! This time music came out of my speakers! I was ecstatic! Until I heard it... The distortion on the right channel! Left channel was fine but the right channel had distortion there was thumping when I turned the amp off and on so I knew there was a blown component and my dc offset would be high on that channel.
Then I got talking to Jason C. Then I ended up diagnosing a bunch of issues and upgraded/modified the amp!
First of all, I removed the xover board completely and added SpeakerCraft rca jacks. Jason was explaining that the rca signals go through a bunch of components and junk and the signal would be better if I could bypass the board completely. Most headunits have DSP so really, I’d rather use that then the analog xover. As well, ribbon cable was tough and brittle almost and I ended up breaking the solder points on both the xover board and main board as I was working on both sides of the board. Jason had kindly helped me by printing a set of PVC xover delete plugs to cover the case holes that are affected when you remove the daughter board. He mailed them to me (took over a month from US to Canada via USPS and Canada Post) and I patiently waited to fill the holes! I used a pair of old PG rca’s and used them to connect the new rca jacks to the main board pins. I ended up breaking the solder points a few time while I was soldering the board, I got fed up and finally put a Molex header on the board and connector to the rca’s so I can remove them easily and not ruin my board with all the re-work on the solder points.
The major issue was a couple or resistors failed and were crispy like bacon on Sunday brunch. I ended up opening the heatsink isolators and tested each fusible resistor, diodes and output. Under the sinks, I found everything ok. Before putting the plates back on, I cleaned all the paste and put new dowsil paste. I found a couple of 51R fusible resistors that opened and one resistor with high value in the predriver stage. These 51R fusible resistors were replaced with flame resistant Vishay resistors on both channels. As well a few of the predriver resistors that were burnt, I replaced (887R and 475R) them high-quality Vishay flame resistant types. The distortion was now dealt with, but I ended up with a little DC offset (on both channels). With Jason’s guidance and expertise, I ended up replacing the diff pair trannies and ordered enough to match the transistors. These OEM transistors are obsolete, so I ended up referred to use A992 and C1845 transistors from Fairchild. Then I ended up changing the TO220 predrivers with Sanken 2SA1668 and 2SC4382 transistors and current source trannies with 2N4403 and 2N4401 as well on both channels. The coupling caps are replaced with Nichicon MUSE wet caps too. Since I replaced so much of this stage of the amp, I decided to change the diodes 1N4002 (two per channel) as well. After all of this, I had to set my bias voltage. Both channels are now set properly and used Jason’s guidance once again!
The fan was also replaced with a new ADDA fan and I replaced the fan resistor from 2W that was originally installed by the factory to 1W to match the newer ZX350v2.
Thanks to Jason and his amazing knowledge about PG amps, I ended up with a highly upgraded/modified/customized ZX350! But lastly, Jason thought I might wanted increase the SQ and upgrade the OP-AMP’s so I thought… Why not! So, my last purchased was a pair of Burr Brown op amps on sockets (so many I can switch them one day and experiment).
In summary:
-Custom made clear plexi windows. (I made a form and heated the plexi with heat gun).
-Nichicon Power Caps and Rail Caps
-Nichicon MUSE and UHE Coupling Caps (all)
-Sanken TO220F predriver transistors (both channels)
-Fairchild matched diff pair transistors A992/C1845(both channels)
-Fairchild current source transistors (4401 and 4403)
-1N4002 diodes
-Burr Brown Op-Amps
-Vishay Dale resistors
-ADDA fan and 1W resistor
-Adjusted bias
-rebuilt/cleaned sensitivity and bass boost pots.
-Molex header and connector for xover pins on main board
-SpeakerCraft RCA jacks
-Customized case hole covers for removed xover board.
-Maybe even more but probably forgot!
I big shout out to Jason for answering EACH of my questions and prompt responses. This overhaul took over 60 days for parts, time and patience!
I hope this can help someone else how has the same issues with this type of amplifier.
Stay safe.
Attachments
pg_amp resistors.jpg
pg_amp rail caps.jpg
pg_amp power caps.jpg
pg_amp opamps.jpg
pg_amp fuse resistors.jpg
pg_amp fan.jpg
pg_amp covers.jpg
pg_amp cover.jpg
pg_amp coupling caps.jpg
pg_amp cover1.jpg
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