I was helping my dad revive his old spa during the holiday. After some minor plumbing work, the spa was biased on. The control board works fine for 30 seconds, then goes unstable. There is a 7805 being used to regulate 18V to 5V for chip bias that is overheating and dropping out. There are only a few items being run off the 5V bus, and 7805's have a 2A rating. (see list of items on 5V bus below)
I am guessing that maybe the output cap has become leaky overtime?
Its got a big 2200uf, 35V electrolytic for an input cap and a tant 104 on the output. THink its the electrolytic. I dont know how to check ESR.
Is there a way to determine where the current is going?
Hooking a current probe to the output leg of the 7805 would determine the total draw, I think?
Any ideas. More details below.
The board worked 12 months ago, and has just sit. I cant see buying a new one for $500 from a spa dealer for a board that has a $50 bom cost.
I dont have a schematic, customer serive guys wouldnt give me one either, but studying the basic functionality it can described it as follow. All through hole parts, easy to probe .
AC in to transformer primary, secondaries run through a bridge to generate 18V.
18V use for coil voltage on various relays (pump, heater, light, blower)
7805 used to generate 5 from 18V. 5V used to bias various chips.
Here is what is on the 5V bus: HD404316D19S(4 bit controller), two HCF4001BE (NOR chips), HEF4521BP(freq divider), ULN2003 (tranistor pack), and a little comparator chip.
Thanks for any help.
I am guessing that maybe the output cap has become leaky overtime?
Its got a big 2200uf, 35V electrolytic for an input cap and a tant 104 on the output. THink its the electrolytic. I dont know how to check ESR.
Is there a way to determine where the current is going?
Hooking a current probe to the output leg of the 7805 would determine the total draw, I think?
Any ideas. More details below.
The board worked 12 months ago, and has just sit. I cant see buying a new one for $500 from a spa dealer for a board that has a $50 bom cost.
I dont have a schematic, customer serive guys wouldnt give me one either, but studying the basic functionality it can described it as follow. All through hole parts, easy to probe .
AC in to transformer primary, secondaries run through a bridge to generate 18V.
18V use for coil voltage on various relays (pump, heater, light, blower)
7805 used to generate 5 from 18V. 5V used to bias various chips.
Here is what is on the 5V bus: HD404316D19S(4 bit controller), two HCF4001BE (NOR chips), HEF4521BP(freq divider), ULN2003 (tranistor pack), and a little comparator chip.
Thanks for any help.