Hi all
This receiver developed a bad crackle in one channel which I fixed by replacing the output chip. Now it works OK until it is switched off and then a low frequency oscillation pumps the speaker really hard until the power supply caps discharge after about two seconds.
Any suggestions?
Thanks
Rob
This receiver developed a bad crackle in one channel which I fixed by replacing the output chip. Now it works OK until it is switched off and then a low frequency oscillation pumps the speaker really hard until the power supply caps discharge after about two seconds.
Any suggestions?
Thanks
Rob
STA-7
Hi Hugo
Thanks for the reply.
Wouldn't a power supply problem affect both channels?
My fault is in one channel only.
Cheers
Rob
Hi Hugo
Thanks for the reply.
Wouldn't a power supply problem affect both channels?
My fault is in one channel only.
Cheers
Rob
Hi rpapps,
Interesting problem. Was the chip an exact replacement? I mean the exact same part number - no subs or replacement brand. What was the chip number?
It sounds like the on board muting is not happening if this chip has it. A leaky cap used as a DC block may cause this also.
-Chris
Interesting problem. Was the chip an exact replacement? I mean the exact same part number - no subs or replacement brand. What was the chip number?
It sounds like the on board muting is not happening if this chip has it. A leaky cap used as a DC block may cause this also.
-Chris
This info comes from an paper lying around here, I have no experience with the amplifier. It also says to check for a short or nearly short between pin 1 & 3 of the output IC's. It's not a big deal to change four diodes, one never knows. 🙂
/Hugo
/Hugo
Hi Rob,
Asked a friend about your amp. The original chip is HA-1370 - NLA. Check the solder connections and traces for one. Check the 1uF coupling caps, actually, remove both to see if the fault remains.
-Chris
Asked a friend about your amp. The original chip is HA-1370 - NLA. Check the solder connections and traces for one. Check the 1uF coupling caps, actually, remove both to see if the fault remains.
-Chris
STA-7
Hi Chris & Hugo
The replacement chip is a genuine Hitachi HA-1370.
There is a swith-on muting circuit but it is common to both channels.
I have replaced the power supply diodes and checked all capacitors with an ESR meter. Even after >20 years, they still read good as new. (I hate to throw anything away)
I've gone over the board with a magnifing glass looking for dry joints or cracked tracks.
I guess the next step is to order another replacement chip.
Thanks for all your input.
Cheers
Rob
Hi Chris & Hugo
The replacement chip is a genuine Hitachi HA-1370.
There is a swith-on muting circuit but it is common to both channels.
I have replaced the power supply diodes and checked all capacitors with an ESR meter. Even after >20 years, they still read good as new. (I hate to throw anything away)
I've gone over the board with a magnifing glass looking for dry joints or cracked tracks.
I guess the next step is to order another replacement chip.
Thanks for all your input.
Cheers
Rob
Hi Rob,
Just for chuckes and grins, pull the 1uF input coupling caps out and try it. They may still be leaky. I use a $6500.00 HP LCR meter to check caps, I don't trust anything less anymore. Your ESR meter may not catch leakage in high impedance circuits.
Besides, caps are cheaper than chips.
-Chris
Just for chuckes and grins, pull the 1uF input coupling caps out and try it. They may still be leaky. I use a $6500.00 HP LCR meter to check caps, I don't trust anything less anymore. Your ESR meter may not catch leakage in high impedance circuits.
Besides, caps are cheaper than chips.
-Chris
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