i recently acquired an intermittently working LEADER LDC 824 frequency counter in a deal that is hard to resist (reads from 10hz to 520mhz)
sometimes it works (reads frequency) after 20mins warmup, sometimes after an hour other times it wouldn't work even after 2hours warmup time. Also at times it works even when the set is cold then suddenly stops working as it warms. it simply displays 0.00000, all the buttons seem to respond except that it doesn't read frequency
but when it happens to work, it works perfectly and reads as accurately as my other counter (a radioshack portable counter, signal source is a vhf handheld radio)
i can't find a service manual or even a user manual, the closest i can get is a user manual for LDC-823 (250 mhz) but it seems to be different
first course of action is to look for cold solders, and discovered that the unit has been resoldered recently and i can't find any loose/cold solders and no obvious physical defects
next, checked for supply voltages, found them to be spot on (5v, -12v, -19v, -38v, etc)
then i checked for hi-esr caps using a homebrew esr meter, found none except for a 33uf 16v tantalum cap which read 2ohms while the other same value cap read .5 ohm
internal oscillator reads exactly 10.0000 mhz on my other counter, probed it on the bnc post at the back of the unit
thinking that this might be a thermal problem, i used a hot air desoldering station to heat up one IC/transistor at a time to provoke the unit but none seems to react with heat
i am not willing to give up yet, even with lacking diagrams and limited test equipment and not so strong foundation on digital circuits and hard to find parts, i humbly seek for assistance, help me out what and where to look for, will do the hardwork and learn at the same time. a service manual would be greatly appreciated. if it can't be repaired i just want to know what went wrong, thanks!
sometimes it works (reads frequency) after 20mins warmup, sometimes after an hour other times it wouldn't work even after 2hours warmup time. Also at times it works even when the set is cold then suddenly stops working as it warms. it simply displays 0.00000, all the buttons seem to respond except that it doesn't read frequency
but when it happens to work, it works perfectly and reads as accurately as my other counter (a radioshack portable counter, signal source is a vhf handheld radio)
i can't find a service manual or even a user manual, the closest i can get is a user manual for LDC-823 (250 mhz) but it seems to be different
first course of action is to look for cold solders, and discovered that the unit has been resoldered recently and i can't find any loose/cold solders and no obvious physical defects
next, checked for supply voltages, found them to be spot on (5v, -12v, -19v, -38v, etc)
then i checked for hi-esr caps using a homebrew esr meter, found none except for a 33uf 16v tantalum cap which read 2ohms while the other same value cap read .5 ohm
internal oscillator reads exactly 10.0000 mhz on my other counter, probed it on the bnc post at the back of the unit
thinking that this might be a thermal problem, i used a hot air desoldering station to heat up one IC/transistor at a time to provoke the unit but none seems to react with heat
i am not willing to give up yet, even with lacking diagrams and limited test equipment and not so strong foundation on digital circuits and hard to find parts, i humbly seek for assistance, help me out what and where to look for, will do the hardwork and learn at the same time. a service manual would be greatly appreciated. if it can't be repaired i just want to know what went wrong, thanks!
