# rebuilding/possibly looking to upgrade an older memphis pwer reference



## shackleford (Feb 24, 2013)

so ive got an older memphis pr150.2 the black one with the chrome shroud(?). i was walked through the troubleshooting process by 2 people over facebook. one had me test whether or not the power supply was supplying voltage to the middle leg of the output transistors(fets?) and i got i wanna say 29.8V?? i forget if he had me do ac or dc. second person had me pull the output transistors from the board and do a voltage drop test in diode check to see if they were ok. all the results from this testing were all over the place and he said they were bad. i wanna say i got one or two good readings across pairs of legs not whole transistors out of the whole bunch of 16 to be tested. the were all either abnormally high .7v+ or abnormally low <0.3v.EDIT retested tonight and found that all the a1693s read OL on diode check from the middle to outer leg. otherwise all the other readings on everything was fairly consistent(within .005V). so ive looked into replacing them and ive found the 2 sold in a pair on ebay for $5.50/pair of c4466 a1693, but its from singapore.... thats the downfall.

the 2 types of transistors are c4466 and a1693 on the output side. there are two of each per channel totaling to 4 of each. and the transistors in the power supply are irfz44n, there are 4. is there any room for improvement? and are there any mild upgrades for the output side that are available in quantities less than 5 in the united states?

the amp was my second amp and i mistreated it and clipped it to death. it sat in my garage fairly useless for a while. before i decided to tear into it, it would power on and you could feed it a signal and max the gain. i know this doesnt mean much but it does mean it could create rail voltage without going into protect. no i did not think to measure the voltage it could produce. but as soon as a load(speaker) was connected it would hop in and out of protect at very low gain levels. one channel you couldnt run it at anything but minimum or itd start jumping in and out. the other channel you could get maybe an 1/8th turn on the gain before itd start hopping in and out. i know i keep referencing the gain as a volume knob and this will be one of my first post but the signal i was feeding the amp to test it was directly out of my phone through a 3.5mm to rca cable. so the gain pretty much would have to be maxed to match the input level to the amp. i doubt im getting more than 0.5v out of my phone lol

could i get a1694/c4467 or even a1695/c4468? or would these just fry the rest of my board? does anybody have any experience ordering components from singapore off of ebay?


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## shawnk (Jan 11, 2010)

Not sure about the output transistors (never heard of those part numbers before... pics?), but right off the bat, you can upgrade the power supply fets with IRFz48 fets, or even better.. IRF3205 fets (gate resistors will likely need to be changed however)

Please keep in mind though, upgrading the power supply fets won't necessarily gain you anything other than slightly more reliability.


btw...there is quite possibly going to be a DiyMobile meet and greet in VA Beach this summer....perhaps you could join us!


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## ATOMICTECH62 (Jan 24, 2009)

The 93's are a more robust transistor then the other two.
If the amp comes on and puts out signal but shuts down when a load is connected,it could be an emitter resistor that is open.But without a scope you will never be able to pinpoint the problem.
Those older amps use a resistor/zener diode ciriut for the +/- 15 volt supply and they go bad a lot showing similar problems.

I could do it for $50 if you pick up shipping.


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