I’m having a look at a HK670 from 2001 for my brother-in-law.
The symptom is intermittent cutting out of both channels. I’ve searched forums and can’t find a common fault, but have a few starting points.
Two of the caps are bulging and one of the resistors looks to have some corrosion in the leads, so they will be replaced first.
Curious though, I have got the service manual and there’s a marking I’ve never seen before for a cap in a circuit. What does “562M” mean?
The symptom is intermittent cutting out of both channels. I’ve searched forums and can’t find a common fault, but have a few starting points.
Two of the caps are bulging and one of the resistors looks to have some corrosion in the leads, so they will be replaced first.
Curious though, I have got the service manual and there’s a marking I’ve never seen before for a cap in a circuit. What does “562M” mean?
562 is 5600 (5 and 6 and two zero's) and is the value of the cap in pF. M is the tolerance and is -/+ 20%
HK products often suffer from low quality electrolytics and heat problems.
The cost of replacing all these capacitors is very low. Don't even discuss their condition. You can't measure them in cirquit, they may be dry and distorting, but still have regular uF values. If you removed them and they measure fine, they may fail next month...
Second, look for brown coloration of the pcb's. Check from both sides and consider re-soldering anything near. You may relocate hot parts, for example change a heat producing resistor for a new one and have it protrude over the pcb for better cooling= long legs.
The cost of replacing all these capacitors is very low. Don't even discuss their condition. You can't measure them in cirquit, they may be dry and distorting, but still have regular uF values. If you removed them and they measure fine, they may fail next month...
Second, look for brown coloration of the pcb's. Check from both sides and consider re-soldering anything near. You may relocate hot parts, for example change a heat producing resistor for a new one and have it protrude over the pcb for better cooling= long legs.
I have one too, and in that one all the regulated voltage supplies the caps were gone, but the PS caps on the amp modules were fine. I guess it was on standby for most of its life, and then all the lower regulated voltages are constantly on. I think the symptom in that case was hum. I think it's worth replacing them once you're in there.
Great amps IMO, well worth saving! I also have a mod posted here on the forum for those who think the bass is a bit 'loose' with the amp.
Great amps IMO, well worth saving! I also have a mod posted here on the forum for those who think the bass is a bit 'loose' with the amp.