Hello to all members.
I'm repairing an AP System One that has out of spec distortion in part of the of the audio spectrum. I checked with another THD analyzer that the problem is really in the generator and I removed all the add on options (IMD, etc.) to be sure they were not at fault. To be sure I replaced all electrolytic and tantalum capacitors on the generator and power supply without any improvement. In most of the spectrum the distortion is 0,002% or less, jumping to 0,004% from 205 Hz to 2047 Hz, when the "1 KHz" band is selected by U352A pin 1.
Since distortion is OK in all other bands I would say that the two MDAC hybrids are OK and also that the three OP amps in the oscillator loop are OK too.
Have you seen something like that before ?
Thank you !
I'm repairing an AP System One that has out of spec distortion in part of the of the audio spectrum. I checked with another THD analyzer that the problem is really in the generator and I removed all the add on options (IMD, etc.) to be sure they were not at fault. To be sure I replaced all electrolytic and tantalum capacitors on the generator and power supply without any improvement. In most of the spectrum the distortion is 0,002% or less, jumping to 0,004% from 205 Hz to 2047 Hz, when the "1 KHz" band is selected by U352A pin 1.
Since distortion is OK in all other bands I would say that the two MDAC hybrids are OK and also that the three OP amps in the oscillator loop are OK too.
Have you seen something like that before ?
Thank you !
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Hello again.
I kind of answered myself ! After reading again my previous message and reviewing the symptoms I found that R3603 (1 kHz adjust) is intermittent. Just gently tapping on it resolved the problem. It passes all self tests OK now. Just to be sure that the problem will not be back next week I will replace the four pots.
I'm posting this in case it might help another member.
Happy DIY !
I kind of answered myself ! After reading again my previous message and reviewing the symptoms I found that R3603 (1 kHz adjust) is intermittent. Just gently tapping on it resolved the problem. It passes all self tests OK now. Just to be sure that the problem will not be back next week I will replace the four pots.
I'm posting this in case it might help another member.
Happy DIY !
Hi LabGuy
Make sure to use a GOOD "multi contact wiper" pots. If you look through "LinkedIn, Classic AP Audio Systems Group LA" I had a generator band problem that wad a MICA CAP was leaking and it caused the oscillator interment working.
Duke
Make sure to use a GOOD "multi contact wiper" pots. If you look through "LinkedIn, Classic AP Audio Systems Group LA" I had a generator band problem that wad a MICA CAP was leaking and it caused the oscillator interment working.
Duke
Type of pot is important, some of them, like plastic based, exhibit semiconductor properties. Which means non linearity in this context.
Hello Audio1Man and MagicianT.
Hello to all members.
Follow up on previous message. I replaced the trimpot (R3603) with the original part number which is a cermet trimmer (Bourns 3386P-1-503LF) it is easily available at low cost, around 3$. It passes all tests now, so a good job done.
Thank you for your comments and suggestions.
Hello to all members.
Follow up on previous message. I replaced the trimpot (R3603) with the original part number which is a cermet trimmer (Bourns 3386P-1-503LF) it is easily available at low cost, around 3$. It passes all tests now, so a good job done.
Thank you for your comments and suggestions.
Hi LabGuy
Since you have a AP System One you should join the "LinkedIn, Classic AP Audio Systems Group LA", it has loads of AP info and users.
Duke
Since you have a AP System One you should join the "LinkedIn, Classic AP Audio Systems Group LA", it has loads of AP info and users.
Duke