hi guys i have a rotel RB-870 with what i believe is a broken transformer, among other things.
this model of amp has 2 BANDO T-180GBE11-EJX transformers, when i pass current through them, one produces less than one tenth of the voltage of the other, while the current's going in are the same. the bando company is still trading!! unfortunately they are located in Malaysia. a google search yields none for sale.
my questions are- is it possible for me to fix at home? and is it worthwhile doing so? how difficult would it be?
i have sent an email to a transformer "rewind" company, and am awaiting a reply (hopefully not with a large quote).
any advise would would be appreciated.
gaz
ps i'm quite new to diy audio repair, never actually built an amp (yet)
this model of amp has 2 BANDO T-180GBE11-EJX transformers, when i pass current through them, one produces less than one tenth of the voltage of the other, while the current's going in are the same. the bando company is still trading!! unfortunately they are located in Malaysia. a google search yields none for sale.
my questions are- is it possible for me to fix at home? and is it worthwhile doing so? how difficult would it be?
i have sent an email to a transformer "rewind" company, and am awaiting a reply (hopefully not with a large quote).
any advise would would be appreciated.
gaz
ps i'm quite new to diy audio repair, never actually built an amp (yet)
Have you looked for a service manual?
https://www.google.com/url?sa=t&rct...e-Manual.pdf&usg=AOvVaw0bOvlxSkiHDuAC70GosJPG
This shows a single transformer with 2 secondaries each 40-0-40V.
Total power consumption is given as 500W.
As your model has 2 identical transformers, you could measure the voltage from the working one and find a transformer that matches the voltage and the physical size.
However, the cost might be prohibitive. A toroidal transformer might be easier to source if it will fit in the same space.
https://www.google.com/url?sa=t&rct...e-Manual.pdf&usg=AOvVaw0bOvlxSkiHDuAC70GosJPG
This shows a single transformer with 2 secondaries each 40-0-40V.
Total power consumption is given as 500W.
As your model has 2 identical transformers, you could measure the voltage from the working one and find a transformer that matches the voltage and the physical size.
However, the cost might be prohibitive. A toroidal transformer might be easier to source if it will fit in the same space.
How did you measure this? Did you have any load on it?
If it was open circuit with a digital meter, chances are there is a break secondary winding somewhere. The secondary winding is usually on top, so you might be able to find it
Brian
hi guys, thanks for the replys
my amp is the 870 not 870bx, i have tried to upload the manual but it exceeds the .pdf allowable file size.
after posting i realized that when i tested the transformer, i had not disconnected the fuses which i believe has given me a false belief that the transformer is faulty, so i retested with fuses disconnected and both are exactly the same. when i tested i used "variac"(made from fan speed controller) and a light bulb in series. i only put about 40 volts through it and there was no load. after reading Brians message i tested for continuity and both were the same(0.6 Ohm secondary's) but, when i re-connect the fuses the bad side drops to 0.4 Ohm. so i'm begging to think the transformer may be ok.
re- other faults i have some transistors that have blown, and could do with a hand locating them. i have a couple of meter's and a secondhand scope, but TBH only know the basics of how to use them.
any advise would be welcomed
gaz
my amp is the 870 not 870bx, i have tried to upload the manual but it exceeds the .pdf allowable file size.
after posting i realized that when i tested the transformer, i had not disconnected the fuses which i believe has given me a false belief that the transformer is faulty, so i retested with fuses disconnected and both are exactly the same. when i tested i used "variac"(made from fan speed controller) and a light bulb in series. i only put about 40 volts through it and there was no load. after reading Brians message i tested for continuity and both were the same(0.6 Ohm secondary's) but, when i re-connect the fuses the bad side drops to 0.4 Ohm. so i'm begging to think the transformer may be ok.
re- other faults i have some transistors that have blown, and could do with a hand locating them. i have a couple of meter's and a secondhand scope, but TBH only know the basics of how to use them.
any advise would be welcomed
gaz
Sounds like the transformer is ok
I would take the fuses out and measure the input of the bridge rectifier. This should be high resistance as most meters won’t give enough voltage to turn on the diodes. I would then use diode test on your meter to check the bridge rectifier itself
Brian
I would take the fuses out and measure the input of the bridge rectifier. This should be high resistance as most meters won’t give enough voltage to turn on the diodes. I would then use diode test on your meter to check the bridge rectifier itself
Brian
hi again Brian
just checked it and, it seems to have an issue compared to the one on the other channel.
i have one i can scavenge from a another broken amp, which i will use temporarily.
i've got a basic scope, is there a correct procedure for using it to locate any broken transistors ??
gaz
just checked it and, it seems to have an issue compared to the one on the other channel.
i have one i can scavenge from a another broken amp, which i will use temporarily.
i've got a basic scope, is there a correct procedure for using it to locate any broken transistors ??
gaz
Hi Gaz,
I would try to test the transistors in situ using diode test on your meter again - test them as two back-to-back diodes. This isn't always successful and you may have to take some out to see if they are good or not. When you are testing in circuit, there can be so many other paths that the readings don't make sense
Brian
I would try to test the transistors in situ using diode test on your meter again - test them as two back-to-back diodes. This isn't always successful and you may have to take some out to see if they are good or not. When you are testing in circuit, there can be so many other paths that the readings don't make sense
Brian