For the Love of Crown PSA-2's

[CaseyWKC]

I recently came into around 16 of these or so.

I repaired four, maybe five?

Customer gave me the rest, two or three are so bad they're parts.

Three are PSA-2's two are PSA 2HXs.

I have repaired plenty of these now,

every time I disassemble the output modules and reassemble with new paste, they don't power on.

I get a short.

I'm using the exact same output transistors with the exact same spacers between the middle output modules specified in the service manual.

I swear to God I have read all 126 or whatever pages.

What the hell am I doing wrong?

 

[twiiii]

I don't have the answer for you, but have seen the issue before with my PSA2 and DC 300A's back in the 70's and 80's. Fortunately, Crown was still around and when our three techs could not get my amps fixed I packed up my Crowns and sent them to the factory. They were out of warranty! But Each time they came back with a 5 X 5 inch bag full of small transistors small caps and diodes at no charge. But not one output transistor or emitter resistors had failed. There might be a few signal diodes and a power supply diode included. They were fixed each time at no charge. A sheet was included telling me they had restored the unit to like new with the results of the tests they had run. They never said why the amps had failed or if components were the issue. Needless to say when Crown was bought by Harmon from the Church I got rid of my Crown amps and returned to Mcintosh amps without auto-formers. My speakers at the time didn't like amps with low damping factors. There was one exception, the infamous Mcintosh MC 3500 tube amp rated at 350 watts and put out 480 before clipping.

 

[CaseyWKC]

I don't have the answer for you, but have seen the issue before with my PSA2 and DC 300A's back in the 70's and 80's. Fortunately, Crown was still around and when our three techs could not get my amps fixed I packed up my Crowns and sent them to the factory. They were out of warranty! But Each time they came back with a 5 X 5 inch bag full of small transistors small caps and diodes at no charge. But not one output transistor or emitter resistors had failed. There might be a few signal diodes and a power supply diode included. They were fixed each time at no charge. A sheet was included telling me they had restored the unit to like new with the results of the tests they had run. They never said why the amps had failed or if components were the issue. Needless to say when Crown was bought by Harmon from the Church I got rid of my Crown amps and returned to Mcintosh amps without auto-formers. My speakers at the time didn't like amps with low damping factors. There was one exception, the infamous Mcintosh MC 3500 tube amp rated at 350 watts and put out 480 before clipping.

appreciate the insight there but yeah, I need a bit more to get these guys going.

Really want to haha.

Thank you!

 

[CaseyWKC]

I should also add the PSA 2 outputs all measure with an hFe around 15-70, a couple of the NPN modules I found in these 2HX's have an hFe of 300+!

By a couple I mean seven or so between each negative output module (might be positive I sometimes confuse the two that have all NPN's until I pull up a picture or the schematic).

 

[CaseyWKC]

Hey everyone, update here.

All is well with the PSAs! - my issue wasn't hFE or any of that nonsense, my dbt was letting me know there was a short and preventing the units from powering on yes, but it was of my own doing.

I ordered some shitty mica insulators from amazon and more than half of them came cracked. I chose to use the ones that looked solid anyways instead of just going through the trouble of returning and between that and my tendency to sometimes overtighten things, it was shorting through to the energized heatsink the output modules were mounted on.

Replaced with some quality insulators and didn't tighten as hard (just hand tightening) and they all powered right up. Got bias adjusted to 2.5mV, adjusted offset, stressed them, and called it a day when they held up.

To shed some light on the PSA-2XH thing that confused me, the output modules and rail voltage are the only things different about them. The output modules must have a higher turn on speed, apparently that is part of Crown's grading process. The Crown facebook group had this image I will attach as well regarding output module changes, names, and numbers/etc.

Rail voltage is 95v on the HX compared to the 75v on the Crown PSA-2's, and apparently there are ways to modify standard PSA-2's to achieve this as well, though I haven't looked into this yet.

Anyways, thanks all!

 

[toddalin]

The line transformer has two sets of windings..., American @~120 volts and Japanese @100 volts. When ShowCo did a gig in Japan they converted over to the Japanese windings. When they returned, they forgot to re-wire them and when powered up, nothing blew. But, the rail voltage had increased and they picked up a bunch of headroom/power at higher impedance settings. There may have been a few changes made after this to accompany the higher rail voltage (e.g., slightly higher voltage filter caps?).

I say at higher impedance settings because the amp is still limited to its 20 amp input which will ultimately determine the power at the impedance. BTW, I run my PSA-2XH bridged in mono at 12 ohms, so I don't pull near 20 amps and can take advantage of the extra power available at that impedance.

 

[Blue Shadow]

Replaced with some quality insulators and didn't tighten as hard (just hand tightening)

Check the spec sheet for transistor mounting bolt torque.

It almost says so loose you think it will fall out but is really 6 INCH-Pounds

https://www.ti.com/lit/an/sboa020/sboa020.pdf.

I think most non-techs and some techs on ak are over-tightening the mounting screws. There is no way that amount of torque will cut through a silicone pad, but some have done it.

How many repaired amps did you end up with?

 

[CaseyWKC]

Check the spec sheet for transistor mounting bolt torque.

It almost says so loose you think it will fall out but is really 6 INCH-Pounds

https://www.ti.com/lit/an/sboa020/sboa020.pdf.

I think most non-techs and some techs on ak are over-tightening the mounting screws. There is no way that amount of torque will cut through a silicone pad, but some have done it.

How many repaired amps did you end up with?

Will do! Thank you!

This is actually still an issue while repairing I’m just taking my time now that I know what the issue is.

I should have three up and running by the end of the next couple of days given the amount of outputs I have left.

Some are the not recommended 5481 or 5841 whatever it is so I will have to order some new outputs for the last one when I have the extra cash.

If it specifies it should feel so loose it should almost fall out I’m over tightening everything and that is concerning!

 

[Blue Shadow]

If it specifies it should feel so loose it should almost fall out I’m over tightening everything and that is concerning!

Well it doesn’t use those words but once you torque them down to spec you will feel they might just. 4-7 inch-pounds isn’t much. But then I’ve been calibrated for automotive work in the 35 foot-pound range.

 

[CaseyWKC]

Well it doesn’t use those words but once you torque them down to spec you will feel they might just. 4-7 inch-pounds isn’t much. But then I’ve been calibrated for automotive work in the 35 foot-pound range.

It was a mix of too much torque and the screws for the middle module making contact with the heatsink, yeah I will be more mindful going forward!



Also after finally working up the courage to trust them powering my Aerials this thing sounds DAMN good.

It has the woofers moving like I've never seen from another amplifier. Truly a two ohm capable amp, I cannot wait to get the second XH I have going and mono block these. The only legitimate concern home audio users will have is the fan, it does get loud under load. But to be fair if you're driving something loud enough to engage the high speed fan then you aren't going to hear it anyways.

I have been a huge fan of my Kenwood 3300D for years but this is making me think.

 

[Blue Shadow]

The SA-2/PSA-2/PSA-2XH will control woofers and make them sound righteous. The high end can falter a bit compared to a top quality amp as the McCormack DNA-1 and Luxman MB3045 both sounded a bit better but they lack 100 watts a side for the 1 and 215 a side for the 3045.

They are nice solid amps and I didn’t know they blow up and need repair. But if one trips over a dozen of them, we know they were not treated as regular hi-if gear. Glad you got em going and enjoy the tunes.

 

[CaseyWKC]

The SA-2/PSA-2/PSA-2XH will control woofers and make them sound righteous. The high end can falter a bit compared to a top quality amp as the McCormack DNA-1 and Luxman MB3045 both sounded a bit better but they lack 100 watts a side for the 1 and 215 a side for the 3045.

They are nice solid amps and I didn’t know they blow up and need repair. But if one trips over a dozen of them, we know they were not treated as regular hi-if gear. Glad you got em going and enjoy the tunes.

Guess I got ahead of myself a bit here too.

The first PSA 2XH is still kicking no problem, but the other PSA 2XH is suffering from the same problem I had with the others.

Still a short somewhere between the heatsink and the output board, I can’t find it, I can’t pinpoint it. It seems to happen at random depending on the tension of the screws. I can’t determine which transistor it is and at this point I have invested more time than I am comfortable with and am considering parting the rest out as I’ve had them so long.

I am pretty sure I just lost all four outputs in my negative channel after thinking the short was no longer there and confirming this with my MM.

R401 burnt up and it took the pre driver with it.

Going to step away from these for a couple of weeks again and think things over.

Beyond frustrating.

 

[powerman]

Have 8 of those PSA 2XH ‘s also and not been used in 10 yrs. Following your thread as I will slow start them this summer and see what will work after this amount of time. Ours all have a 30 amp plug and badge rating 30 amps on the back. Good luck with your endeavors

 

[CaseyWKC]

Have 8 of those PSA 2XH ‘s also and not been used in 10 yrs. Following your thread as I will slow start them this summer and see what will work after this amount of time. Ours all have a 30 amp plug and badge rating 30 amps on the back. Good luck with your endeavors

Only word of advice here is don’t take apart any of the output modules if you don’t have to.

I didn’t have a single issue with a single output module I didn’t have to take apart to clean and reapply grease.

I had at least one issue with every single one I did.

Anything can be tested in circuit so just avoid the mistakes I’ve made. lol.

 

[powerman]

Only word of advice here is don’t take apart any of the output modules if you don’t have to.

I didn’t have a single issue with a single output module I didn’t have to take apart to clean and reapply grease.

I had at least one issue with every single one I did.

Anything can be tested in circuit so just avoid the mistakes I’ve made. lol.

Thanks somewhere around here are a couple of complete NOS modules I bought years ago too. Also faceplates for PS400’s and 200’s.