Hi can anyone give me advice on how to repair an Arcam a65+, The symptoms are, thump sound at turn on or off and very high DC offset of over 700mv in the right channel it plays fine for ten minutes and then switches off and comes back on and carries on playing. The left channel is fine.
If someone can give me advice on where I need to be looking that would be great. Thanks.
If someone can give me advice on where I need to be looking that would be great. Thanks.
Ok I had a look c702 is reading 1mv on the + side and 9.6mv on the - side. Since c705 is flush to the board I had to read it from c724 because they are wired in parallel. It reads 600mv on the + side and 1.6mv on the - side. Rv700 reads 1.1 volts on both sides and the ohms test shows it tracking well from 0 ohms to about 80. What do think replace c705? Thanks for your help.
I have some fm Panasonic caps 100uf 25v, should I put one of those in to test? The original is 100uf 16v silmic II but of course I don't have one of them. Any advice would be helpful. Thanks.
So I finally found and repaired the right channel, but now I have noticed a problem with the left channel. At switch on there is a slight thump. Putting my probe on the output terminal. I have noticed as soon as the relay clicks in it reads 110mv for a second then 64mv and finally 8mv all within 3 seconds. Then of course it slowly climbs to no more than 20mv.
Also adjusting either bios pots makes no difference to the dc offset.
Any ideas?
Also adjusting either bios pots makes no difference to the dc offset.
Any ideas?
I also have one Arcam A65+ with 4,2V dc on left chanell output. I have measured almost all transistor and found no failure. I changed 10uf c625 and amp was going on for 3 seconds and again in protection. I have 1,2v on one side of capacitor and -1.2v on perfectly working Right channel but on Left side -39v and on other side of a cap +5.4v...so then i have around 4.8v on bias trimer and around 4.2 on output and around 4,7v on both bias points. I can post later picture schematic with testpoints to easier clarify where are differences in testpoints.
As i wrote when i was replaced C625 10uf elco it was turn on for 3 seconds than again in protection mode.
Q615 appears to be failed, as your measurements show base to emitter (-38.9 -4.7)= -43.6V. Your working channel shows 2V, much more reasonable.
You mentioned measuring the transistors--- how did you test them?
Q615 is the likely culprit, but I suggest an additional in-circuit test. With power off, use ohmmeter to set RV600 to minimum resistance so that bias current is minimized. Then apply power and try measure base-emitter voltage directly at Q615 leads. The objective is to rule out any open connections and prove the transistor itself is at fault. Be very careful, as a slip with the probes can provoke massive damage. A safer procedure is to solder-tack test wires with power off and bring them out so a safer place to make the powered measurement.
Good luck!
You mentioned measuring the transistors--- how did you test them?
Q615 is the likely culprit, but I suggest an additional in-circuit test. With power off, use ohmmeter to set RV600 to minimum resistance so that bias current is minimized. Then apply power and try measure base-emitter voltage directly at Q615 leads. The objective is to rule out any open connections and prove the transistor itself is at fault. Be very careful, as a slip with the probes can provoke massive damage. A safer procedure is to solder-tack test wires with power off and bring them out so a safer place to make the powered measurement.
Good luck!
I also thought first that output darlington is partly damaged, but when i compare multimeter diode test values were the same on both pairs. So today i deceided to demount whole pcb out, because i did not find any faulty part. Look what i found when i turn around the pcb around 😉
