EV PA4150L power amplifier - repairs

Amps, Cabs, Speakers, etc
Post Reply
User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

EV PA4150L power amplifier - repairs

Post by laurie » Sun Jan 16, 2022 1:20 pm

Last year I picked up a power amp that I was intending to use with my Fractal AX8.

It is an EV PA4150L - four channels, 160W into 4 Ohms per channel. My intent is to use two of the channels as left-right mid/high, and bridge the remaining two for subs.

I swapped a couple of pedals for it (a 32-OD and a 32-FZ). It was "working" when I got it (but not well).

When I dismantled it for cleaning it was immediately obvious that both cooling fans were seized.
.
20211019_064425sml.jpg
20211019_064425sml.jpg (119.26 KiB) Viewed 7638 times
Last edited by laurie on Sun Jan 16, 2022 1:40 pm, edited 3 times in total.

User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

Re: EV PA4150L power amplifier - repairs

Post by laurie » Sun Jan 16, 2022 1:33 pm

Having the fans seized shouldn't have been a problem - both heatsinks have over-temperature sensing and the amp would have been turning off when it got too hot.

So I ordered two new fans and proceeded to do a thorough clean and test of the amp.

Here is what I found, and what I am in the process of repairing:
  • Fans seized. New fans ordered and and installed.
  • The power-on delay relays for each channel are faulty - the wiring loom in the amp put too much strain on top connector on the relay and the contacts became intermittent. New relays ordered and installed. Wiring re-done to prevent a reoccurrence.
  • One of the channels had a 60 cycle hum. Traced the problem to the power-supply board. Even though the main boards were protected by the over-temperature sensors, the power supply board was not and the power supply to the opamps for one of the four amplifier channels has failed. The board is too burned to repair (see pic below) - the overheated traces fall apart when you attempt to unsolder components. I was able to order a new power supply board from the EV service agent here in Canada and it is ready to fit. I have also ordered a small (30mm x 30mm) fan that I will mount on the power supply board blowing over the voltage regulators to keep the air permanently flowing over them, not just when the main fans turn on.
  • The connectors near the burned area of the board had melted. New connectors ordered and will be fitted with new wiring (the wires going to the melted connectors have become brittle).
  • The level pots were so dirty it was nearly impossible to turn them and I could not even feel the detents. Pots cleaned and lubricated.
I think that's all that is wrong with it - when the replacement connectors come I will put everything back together and test it.
.
20220116_060123sml.jpg
20220116_060123sml.jpg (115.59 KiB) Viewed 7637 times
.
20220115_201157sml.jpg
20220115_201157sml.jpg (149.4 KiB) Viewed 7637 times

User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

Re: EV PA4150L power amplifier - repairs

Post by laurie » Sat Jan 22, 2022 4:50 pm

  • Fans seized. New fans ordered and and installed. FIXED
  • The power-on delay relays for each channel are faulty - the wiring loom in the amp put too much strain on top connector on the relay and the contacts became intermittent. New relays ordered and installed. Wiring re-done to prevent a reoccurrence. FIXED
  • One of the channels had a 60 cycle hum. Traced the problem to the power-supply board. Even though the main boards were protected by the over-temperature sensors, the power supply board was not and the power supply to the opamps for one of the four amplifier channels has failed. The board is too burned to repair - the overheated traces fall apart when you attempt to unsolder components. I was able to order a new power supply board from the EV service agent here in Canada and it is ready to fit. I have also ordered a small (30mm x 30mm) fan that I will mount on the power supply board blowing over the voltage regulators to keep the air permanently flowing over them, not just when the main fans turn on. FIXED
  • The connectors near the burned area of the board had melted. New connectors ordered and will be fitted with new wiring (the wires going to the melted connectors have become brittle). FIXED
  • The level pots were so dirty it was nearly impossible to turn them and I could not even feel the detents. Pots cleaned and lubricated. FIXED
A full test of the audio was successful - clean, crisp, perfect on all channels.

Testing of the cooling fans by running the amp at full-load uncovered one last fault. The cooling fan for the C and D channels does not work. The connector for the fan has 24VDC but when the fan is plugged in, the voltage drops to 4VDC. Clearly a fault in the fan drive circuit. Will track that down today.

As always with things like this, it is a "labour-of-love" ... to keep something good out of the land-fill/parts-bin. I guess I've spent about $500 on it so far, which is likely more than it is worth. Plus maybe 20 hours.
pepe - I know you can relate with rebuilding synths :)
.
20220122_094151sml.jpg
20220122_094151sml.jpg (138.5 KiB) Viewed 7577 times
Last edited by laurie on Sat Jan 22, 2022 5:12 pm, edited 1 time in total.

User avatar
Pepe
Posts: 1702
Joined: Thu Aug 16, 2018 2:19 pm
Location: Germany
SBZ: Multi Platinum
Bossarea: Double Platinum
Contact:

Re: EV PA4150L power amplifier - repairs

Post by Pepe » Sat Jan 22, 2022 5:08 pm

laurie wrote:
Sat Jan 22, 2022 4:50 pm
As always with things like this, it is a "labour-of-love" ... to keep something good out of the land-fill/parts-bin. I guess I've spent about $500 on it so far, which is likely more than it is worth. Plus maybe 20 hours.
pepe - I know you can relate with rebuilding synths :)
In the case of my synthesizers it is commonly that I weren't able to purchase one of them in working condition, because of the steep prices nowadays. But of course the personal value increases a lot if lots of hours of labour have been put inside. :)

Great job with the EV power mixer so far! :ugeek:
Pepe at YouTube and Instagram

User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

Re: EV PA4150L power amplifier - repairs

Post by laurie » Sun Jan 23, 2022 3:07 pm

There is a perfect storm of failures in the heat-management systems.

There is a thermostat that turns on the fan - it has failed, so the fan never turns on.

There are thermostats for each channel that turn off the channel if the heatsink temperature rises too far (e.g. if the fan fails) - these have failed, so that the channels never shut down.

So the fan doesn't work, and the channels never shut down, so the heat just "runs away"...

Fortunately the thermostats are cheap and available locally so it can be fixed easily.

If you have found this thread because you have a PA4150L that you are repairing - just replace the thermostats as you are doing the repair. Clearly the original ones are dodgy.

There is no schematic available so I had to make a judgement call about temperatures:
  • I selected a 50C thermostat for the fan. Turns on at 50C and off at 35C. Part number NTE DTC-120
  • I selected a 75C NC thermostat for the over-temperature sensing. Shuts down the channel when the heatsink hits 75C. Part number NTE DTO170.
.
Image2.jpg
Image2.jpg (234.4 KiB) Viewed 7557 times
Last edited by laurie on Tue Jan 25, 2022 4:03 am, edited 1 time in total.

User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

Re: EV PA4150L power amplifier - repairs

Post by laurie » Tue Jan 25, 2022 2:51 am

Picked up the new thermostats today. Initial testing is good - fan turns on when it should.

User avatar
The_Doc
Posts: 467
Joined: Fri Aug 17, 2018 6:02 am
SBZ: Gold
Bossarea: Gold

Re: EV PA4150L power amplifier - repairs

Post by The_Doc » Tue Jan 25, 2022 8:30 am

Great work Laurie ! Really interesting thread.

User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

Re: EV PA4150L power amplifier - repairs

Post by laurie » Wed Jan 26, 2022 1:08 pm

I mentioned it before, but this amplifier is a "labour of love".

The new NTE thremostats are 0.5mm taller than the original ones (even though the paper specifications said they weren't).

To make them fit I've had to completely dismantle everything off the heatsinks and machine "pockets" in the heatsink to lower the thermostats so that they have physical clearance. Not the easiest job - it really needs a $3000 milling machine that I don't have.

Then retest everything. Another 6 hours work.

There is no way I'd want to fix amplifiers "for money"...

User avatar
laurie
Posts: 1663
Joined: Fri Aug 17, 2018 2:07 am
Location: Canada
SBZ: Multi Platinum
Bossarea: Multi Platinum

Re: EV PA4150L power amplifier - repairs

Post by laurie » Fri Jan 28, 2022 2:50 am

Finished.
.
20220127_055340sml.jpg
20220127_055340sml.jpg (99.99 KiB) Viewed 7482 times
.
20220127_063044sml.jpg
20220127_063044sml.jpg (73.77 KiB) Viewed 7482 times

Post Reply