| Electronics > Repair |
| Repairing a half-working amplifier. |
| (1/3) > >> |
| Mint.:
I got a Yamaha HTR-5840 Amplifier which I got off a friend, and its definitely past its use by date and an issue has occurred with it. I am not sure whenever this would be a simple fix or not, but I just want to give it a try because its still working and I am pleased with it otherwise I'll just have to salvage the parts and throw it out. Basically the problem is that it sometimes doesn't want to turn on, this has only started happening recently. I turn the amp off using the mains switch and not the standby button (it still uses electricity in standby mode). Anyways when I turn it on it turns on, but if I were to turn it off at the mains and then turn it on again it wouldn't turn on. It would work after a few hours or so, but not straight after. Sometimes just playing around with the switch works, but thats time consuming. A month back it had the same problem, but I cleaned it on the inside with a vacuum cleaner and then it began working, however then it began to develop the same problem soon afterwards. I am assuming maybe there is a bad capacitor or something inside of it and it would be just a simple fix of replacing that cap and we got a working amp again. Or perhaps there is a cold solder joint there... Any ideas what is going on with this amp? |
| DrGeoff:
Check around the power supply first for bad caps or cracked solder joints. If there's some kind of turn-on delay relay then there might be a cap that is not charging properly any more. |
| David_AVD:
Yes, some of those models develop bad (cracked) joints, especially around the connectors and heavier components. |
| HackedFridgeMagnet:
If you can't find the schematic on the web, it might be a good chance to sketch out the schematic. Not all of it but the mains to the DC power rails. Will the power off and a multimeter you should be able to "bell out" the tracks that are hard to see. Also look for cracked pcbs or connectors falling off, signs of heat or leakage or damage. Check switches to make sure they are working as expected. Check any semi conductors in the area to make sure they are not blown short. Although your intermittant bug doesn't sound like this is the case. Another important thing to do is see if you can reliably reproduce the fault. If you can you have a strong clue as to the cause. If nothing is obvious the next option is probably that you have to work live. Only do this if you are confident you know what you are doing and where potential danger lies. If you are going to work live on the amp you need to have and RCD protected circuit, or an isolation transformer. Always. Also having somebody near you when you are working to turns things off if things go awry, could be handy too. When the unit is powered on, and you have the schematic and you have the unit in it's fault state, you should be able to find the offending components. A quick test is to find the DC power rails. + and -. |
| vk6zgo:
Some older switchmode supplies have a high value resistor which links the mains active with the oscillator part of the switchmode. The idea is that at switch on a bit of mains AC appears at enough level to trigger the thing into oscillation. After some years, the resistor goes high in value,& the trigger function is no longer reliable. If you switch on & off several times,you will sometimes "jag it",the oscillator will start,& the switchmode will operate. I'm sorry about the vague description,but it's years since I worked on this type of circuit,which were commonly used in Sanyo TVs. Barco Picture Monitors used the same idea. |
| Navigation |
| Message Index |
| Next page |