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Phase Linear 700-II repair advice needed

gadget73

gadget73

junk junkie
Subscriber
I'm working on a Phase Linear 700-II for a friend. He shorted the speaker wires together, and I found a shorted output transistor. The rail fuse popped, and it seems to have saved the amp. With the defective transistor out, tests per the service manual for shorts come up OK. It has all original XPL-909 output transistors, which apparently cross to a Delco DTS411 transistor. If I can come up with a genuine Delco part, is there any reason I can't just replace the single bad transistor and make this live again? I would verify the current sharing per the service manual and all that fun stuff.


Before I buy parts, I will fix my transistor tester and see if the rest of the outputs check OK. So far I've only checked them for shorts with my DVM.

Thanks for any input. Solid state is well out of my realm of experience.
 
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Oh, something I noticed. The stickers on the back of the amp call for a 10 amp power fuse, and each of the rail fuses are 5 amp. it has an 8 amp power fuse, and 4 amp 32v rail fuses installed. Should I change those back to the higher rating, or just change out the rail fuses for 4 amp at an appropriate voltage?
 
It's tempting to experiment but with PL700 output topology you'd rather call it 'luck' if after replacing only one shorted output the amp will continue to work reliably and not to oscillate. Most probably it won't work as desired - this amp is indeed sensible on any difference in current sharing, so careful testing is definitely required. But moreover with >100 VDC on rails some power transistors that seemed to look fine after your output stage failure occurred may now get shorted in any moment, giving you tons of DC to the speakers...

There is a specific factory bulletin on this point: http://home.earthlink.net/~dimlay/sitebuildercontent/sitebuilderfiles/outputs.pdf. You must not mix different types of outputs per single channel (upper & lower pole). To save money and time you should rather consider replacing the whole bank of power outputs, in which the shorted transistor was found. Not only the one that has gone. If outputs used are obsolete, then the whole output stage (both channels) calls for replacement... The ON MJ21196's and 95's (depending whether quasi- or fully- comp topology in place) are good subs.

Check again the 700 II Service Manual for troubleshooting details and you may have a look here too: http://www.audiokarma.org/forums/sho...293316&page=17 -> specifically see post #245 and it's attachments.

When you decide doing so, put in the driver first (originally RCA-410's) and bring it up on the dim bulb. A dim bulb tester is a must. A variac will limit voltage, but not current. If everything is fine with drivers installed, put in another row (power outputs) all the way accross, then power on with dim bulb again, then another row accross, etc. Get the bias set close as possible on the first row, but you'll have to adjust it as you go.

There are many posts on the topic here on AK and on http://forums.phxaudiotape.com/forum.php - you have true PL believers there and knowing how to repair this amp. :-)...
 
Damn. I was hoping to get away with a single or maybe a couple transistors. They are indeed obsolete types. It runs the XPL909. I found the Delco part number in the PDF file you linked.

I suspect my friend is not going to want to spring for a set of 20 output transistors either. I guess I can price it out and see what he says. I will bet that he'll tell me to get the one transistor and try it though. I'm not putting it to my speakers for a while. I have a dummy load that I can feed about 80 watts to. I'll just have to run it around that power level for a while to see what happens.

Either way, I'll make up the test leads on my transistor tester tonight and see if that will tell me more about the condition of the output stage. Luckily i have one good set to compare to. Only one of his speaker cables got shorted.
 
I have boxes of XPL-909 transistors I have taken out while converting 400's and 700's to the new White Oak boards. You will not find any XPL-909's and a genuine DTS-411 will cost you 15.00. If you will PM your address I'll send you a hand full of XPL-909's.......BUT as Przem has eluded to, the XPL's are a disaster waiting to happen. On-Semi MJ 21196's have a much greater current rating and much higher SOA and at 3.00 a pop very cheap insurance, especially if you are not running any DC protect in that amp...
 
gadget73 said:
Oh, something I noticed. The stickers on the back of the amp call for a 10 amp power fuse, and each of the rail fuses are 5 amp. it has an 8 amp power fuse, and 4 amp 32v rail fuses installed. Should I change those back to the higher rating, or just change out the rail fuses for 4 amp at an appropriate voltage?
Click to expand...

The factory spec was 10 amp mains in 250 volt rating, the rail fuses are 5amp 250 volt fast blow types.

When convertionmg 700's to the White Oak boards I pre test the stockj configuration to see how robust they are. To do that I actually put 10 amp fast blows in place of the 5 ampers to get a max output at 4 ohms( which is 775 watts both loaded and driven just before clipping) , and they seem to live just fine, so a 5 amp is way under rated output....at 4 ohms anyway. A 5 amp will stay in during the max output test onto 8 ohms...


A trasistor tester will show leaky on those outputs. The only definitive test is the operational curret sharing as indicated in the service mnual...
 
gadget73 said:
Damn. I was hoping to get away with a single or maybe a couple transistors. They are indeed obsolete types. It runs the XPL909. I found the Delco part number in the PDF file you linked.

I suspect my friend is not going to want to spring for a set of 20 output transistors either. I guess I can price it out and see what he says. I will bet that he'll tell me to get the one transistor and try it though. I'm not putting it to my speakers for a while. I have a dummy load that I can feed about 80 watts to. I'll just have to run it around that power level for a while to see what happens.

Either way, I'll make up the test leads on my transistor tester tonight and see if that will tell me more about the condition of the output stage. Luckily i have one good set to compare to. Only one of his speaker cables got shorted.
Click to expand...

I'd follow Lee's advice. He's the expert on PL gears. And buying obsolete transistors you also run a risk of getting fake ones... -> see these links: http://sound.westhost.com/counterfeit.htm and http://sound.westhost.com/fake/counterfeit-p1.htm

Good luck!
Przem
 
laatsch55 said:
A trasistor tester will show leaky on those outputs. The only definitive test is the operational curret sharing as indicated in the service mnual...
Click to expand...

The service bulletin does say that. I just want to see if they all test similar for beta or gamma or neutron or whatever the heck it is transistors use. The sandy version of transconductance :)


Also, I've owned that Hickock 890 for probably 3 years now and have yet to make test leads for it. Finally I have an excuse.


I'll run it by my friend and see what he wants to do. Whats a good source for the MJ21196's ? Are those a drop-in replacement, or do I have to make other changes to the unit? If he wants to go cheap on it, I'll shoot you a PM to take you up on the offer of an XPL909 pull. I do very much appreciate the offer.

If this were mine, I'd probably just overhaul it with better parts, put in a DC protection board because that seems like a good idea, and re-cap it. My friend doesn't tend to believe in spending money to fix things correctly, and I refuse to spend my own money to fix other people's stuff. He wants to play this thing loud through crappy PA speakers. As long as it makes a lot of noise, he doesn't care about much else.

If its inclined to blow 5 amp fuses before it hits full rated power, I'll go with that. I think his speakers are 4 ohm, and who knows what kind of impedance curve they present. I'd rather under-rate the fuses a bit so they blow and hopefully save the amp rather than running it flat-out until the smoke comes out.

Anyway, I appreciate the input guys. I don't mean to sound like I'm ignoring your experience, but its not my call. I'm just seeking info so I can present options to the guy who owns it. I'm not a solid state guy at all, so this is alien territory for me.
 
Oh, something I noticed while I was in here. Is there any reason to not bridge the two sections of the power switch together to increase it's current handling capacity? Looks like there are two sets of NO contacts on the back end of it, and only one set is in use. I presume the NC/NO sets on the front of the switch are low current and should not be used.
 
I was told these were PL. Not sure what for, they are here if they'll help, send a PM please, I probably won't remember to check back. Hope you get it going.
Dan
 

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Recpro said:
I was told these were PL. Not sure what for, they are here if they'll help, send a PM please, I probably won't remember to check back. Hope you get it going.
Dan
Click to expand...

Those are outputs for the Pl 300 Ser II. Also the same output used in the mighty Pioneer SX 1980...
 
gadget73 said:
Oh, something I noticed while I was in here. Is there any reason to not bridge the two sections of the power switch together to increase it's current handling capacity? Looks like there are two sets of NO contacts on the back end of it, and only one set is in use. I presume the NC/NO sets on the front of the switch are low current and should not be used.
Click to expand...

Don't see why not, just make sure they are NO..
 
Also, I've owned that Hickock 890 for probably 3 years now and have yet to make test leads for it. Finally I have an excuse.



I have an old Sencore TR-139B , pretty darn handy...
 
If you need some serious cash, check old e-bay listings , some of those output pairs bring SERIOUS money. You could be sitting on 800-1,000.00
 
gadget73 said:
Oh, something I noticed while I was in here. Is there any reason to not bridge the two sections of the power switch together to increase it's current handling capacity? Looks like there are two sets of NO contacts on the back end of it, and only one set is in use. I presume the NC/NO sets on the front of the switch are low current and should not be used.
Click to expand...

Just talked to Ed Blackwood. He parallels that power switvh on every amp he does that has it. You should also put a 1,000 volt .027 to a .05 uf ceramic cap to keep the arcing down...
 
laatsch55 said:
If you need some serious cash, check old e-bay listings , some of those output pairs bring SERIOUS money. You could be sitting on 800-1,000.00
Click to expand...

There is a never installed 900 display board also...totally forgot they were here until I saw this thread.
 
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