rockford fosgate 500M questions

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lampredi

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Joined 2013
#1
hi, i purchased these,
i removed the bottom cover, and realised some caps are damaged,and one was even removed. im refering to the big caps near power supply circuit ,they are the 4700uf 80vw caps. there are supose to be 4 in total, 1 cap has been removed,
the amp works according to the guy i purchased it from, i never tested it yet.
i want to know what replacement caps do i buy ?
panasonic or nichicom ?
i found this : http://za.mouser.com/Panasonic/Passive-Components/Capacitors/_/N-5g7r?P=1yzvjj0Z1z0wqt9Z1z0x6qa

there are a few variants of the caps 4700/80v ,
i asume those with higher operating temperature range would be good ?
or should i get the nichicom cap as the amp came with originaly ?

i want to buy quality parts and have the amp reliable for many years to come.
i have 2 of these amps and want to re-cap both .
 
#2
105 deg should have longer life. If you can, look up the spec sheet of the original caps. Taking particular note of rated ripple current. Provided you are the same or better with the new caps (and low enough ESR) they will probably be ok.

If the original caps are specifically for SMPS then you might need to make sure that the replacements are ok for SMPS also...

Tony.
 
#3
thank you, i will check and take it from there,
wich would be better between the equivilant panasonic vs nichicon cap ?

both 500m 's will need repair, the one does not power up,and the other plays but has missing cap ( 4700uf 80v cap missing )
my plan is to buy some of the parts myself eg. quality caps,proper fets etc. and send both amps for repair,but with my parts purchased.
dont want rockford repair centre to use cheap parts like caps,fets,
so i will provide my own parts where i can like the caps, and let rockford centre fix the amps. hope i make sense.
 
#4
Difficult to say without comparing spec sheets. It also depends on your goal. By the sounds of it the original Nichicons have not fared well, so replacing them with something with better specs (eg 105deg instead of 85deg or higher ripple current rating) may be better for your goal of longevity.

For Power supply caps, I would say higher ripple current handling, and lower ESR are two things to consider as being superior.

Tony.
 
#7
i have checked the power supply fets in both amps ( i have 2 of them ) and one amp has
IRFz44R 's , while the other amp has IRFZ44 's in power supply.
both amps need repair. so i want to replace all gate resistors,power supply transistors.
output fets,source resistors, SMD transistors ( if needed) .

wich power supply transistors would work best in these amps ? IRFZ40, IRFZ44R,IRFZ44,IRF3205 etc etc ?
output fets are IRF640/IRF9640 .i want to replace all of them and the resistors aswell.
wich output fets will work well with these amps ?
main goal is reliability and power.
 
#8
if you are wanting to change all the transistors and resistors out you should probably go with the IRF3205 with a lower ohm resistor. I think around 47 ohm is what I read. I think that punch used Buzz11s in that amp originally so someone may have already swapped out power supply transistors already. You already have decent fets in the channels irf540/irf9540 were the standard specs used in a lot of amps back then so irf640/irf9540 would be fine to use again unless something's changed in the past 10 years. 500m's are nice amps, I would not buy any parts from ebay. I ordered a batch of irf3205s and they were counterfeit so I usually gets them from Jameco or Digi-Key now. I would not send it in to Fosgate for repair by any means. There are techs here that will do the quality repair you are expecting. Good luck


Oh, and don't buy the cheap transistors, I always buy International Rectifier when possible.
 
Last edited:
#9
jeffb30 said:
if you are wanting to change all the transistors and resistors out you should probably go with the IRF3205 with a lower ohm resistor. I think around 47 ohm is what I read. I think that punch used Buzz11s in that amp originally so someone may have already swapped out power supply transistors already. You already have decent fets in the channels irf540/irf9540 were the standard specs used in a lot of amps back then so irf640/irf9540 would be fine to use again unless something's changed in the past 10 years. 500m's are nice amps, I would not buy any parts from ebay. I ordered a batch of irf3205s and they were counterfeit so I usually gets them from Jameco or Digi-Key now. I would not send it in to Fosgate for repair by any means. There are techs here that will do the quality repair you are expecting. Good luck


Oh, and don't buy the cheap transistors, I always buy International Rectifier when possible.
Click to expand...

thank you,
there's still some reading to do my side, need to understand more regarding these amps. i need the schematics for the following pcb: 0776 d and 0776 e

i realise that one of the amps have resistor R57 removed. i dont know why,but i came across some rockford tech notes that advise to remove R57.(modification notes) see bellow
for 500m/250m:
"Change R40,41 to RM/10-680B. Make R2 a Jumper (0ohm). R57-Removed. Change all output FET's gate resistors to RM/10-101B"

I need to figure out why they recommend this ?
i want to link both amps as one amp,so i asume the internals of both amps should be similer,and NOT have one amp with a few different parts/parts removed....
 
#10
lampredi said:
thank you,
there's still some reading to do my side, need to understand more regarding these amps. i need the schematics for the following pcb: 0776 d and 0776 e

i realise that one of the amps have resistor R57 removed. i dont know why,but i came across some rockford tech notes that advise to remove R57.(modification notes) see bellow
for 500m/250m:
"Change R40,41 to RM/10-680B. Make R2 a Jumper (0ohm). R57-Removed. Change all output FET's gate resistors to RM/10-101B"

I need to figure out why they recommend this ?
i want to link both amps as one amp,so i asume the internals of both amps should be similer,and NOT have one amp with a few different parts/parts removed....
Click to expand...

Maybe the notes were made because the original Motorola fets were soon discontinued after the amp was produced and those were the modifications needed to use replacement fets?? And you assume correctly. Both amps should be identical when linking them. I am by far not an expert but I am learning a lot from this website. I try to help you with what I do know but Perry Babbin Is the man who could confirm most anything you have a question about. I've fixed a lot of amps but I am not anywhere near the skill level of Perry. You could possibly repair them yourself if you could chat with him. He is an genius in his field. It always helps to post pictures of the boards also. Get the pics posted and I'll try to help you and possibly other members can chime in with advice.
 
#11
R57 would have added deadtime. Maybe the decided that it wasn't necessary.

R40/41 are in the differential amp. The changes could have been for a lot of different reasons. One possible reason is not enough range in the biasing circuit.

R2 was between the left and right shield grounds. It could have causing noise problems or they decided that it didn't need to be a resistor.
 
#12
thank you Perry,
im going to concentrate on 1 amp first.it plays but had 1 4700/80v cap removed believe it or not. so im going to add the cap.
im also still in proccess of gaining knowledge regarding amp repairs,reading on your website.( i mailed you regarding the static IP enquiery)

so for now,im just reading/researching ,before i attemp the reapairs myself.
just a quick question though, as this is a mono class ab amp with a big transformer/caps : wich power supply transistors would be best suited without making too many other changes ? reliabilty/power being main goal.
 
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