I checked all the resistors and the diodes and all checked good last part will be the RCA29/TIP29
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Power supply problem need help
- Thread starter Techno1
- Start date
In my experience - I side with Nomad, the Diodes are one of many things in question - you've already replaced just about all the logic in the supply - except for the diodes that form that bridge.
One or two diodes can cause that sag, the AC ripple the 723 is trying to keep from showing up in the output - is why that sag in power is there.
The TIP part - is simply being cut down by the 723's output monitor - so when the load current is low, the voltage is high, so the TIP runs at the rated regulation - there's enough DC voltage peak to peak to let those filter caps smooth out that otherwise heavy ripple that is present the 723 is trying to get rid of.
When a Diode fails - it takes the current cycles and the voltages right along with it, forcing the other half of that portion of the bridge to hold the line at 2X it's rating - so it's only going to fail further - which will take out the 723 - then you're stuck with nothing much more than a battery charger.
One or two diodes can cause that sag, the AC ripple the 723 is trying to keep from showing up in the output - is why that sag in power is there.
The TIP part - is simply being cut down by the 723's output monitor - so when the load current is low, the voltage is high, so the TIP runs at the rated regulation - there's enough DC voltage peak to peak to let those filter caps smooth out that otherwise heavy ripple that is present the 723 is trying to get rid of.
When a Diode fails - it takes the current cycles and the voltages right along with it, forcing the other half of that portion of the bridge to hold the line at 2X it's rating - so it's only going to fail further - which will take out the 723 - then you're stuck with nothing much more than a battery charger.
Ill have to wait hopefully this week the RCA29 will show and replace it and see what happens under load. I'll report back with the results.
Tricky part in a power supply using the 723 chip is to determine whether or not it got clobbered. Our policy was to remove that chip, install a socket and a new 723 chip. The labor to test the old chip in any way would have cost at least as much as just replacing it. My policy for parts with more than three legs is to always use a socket if possible. Circuit board traces are not meant to be reheated more than a couple of times before they begin to lift away from the surface. Using a socket means you won't need a soldering iron if that part ever fails again in the future.
Parts tend to be cheaper than labor, so it's just cheaper to "waste" a new chip that you maybe didn't need than to waste the time testing it.
73
Parts tend to be cheaper than labor, so it's just cheaper to "waste" a new chip that you maybe didn't need than to waste the time testing it.
73
Well I replaced the 723 and the 2n7331 and same results voltage but volts drop to almost 0 when keying a radio. I have the RCA29 on its way and will see what happens.
I will have to wait until the part comes to do some voltage checks its a pain to get to and remove the cover.
I will have to wait until the part comes to do some voltage checks its a pain to get to and remove the cover.
You realize that this power supply has a crowbar circuit.
To see if the system still works, just remove the SCR - if the thing never sags - then the crowbar circuit - including the SCR trigger, has to be checked.
D4 is a 5.6V Zener in that crowbar circuit. Along with R9 - forms a window of "on" operation - as long as the voltage on the positive post of the output, stays above a threshold, D4 pulls power into a limiting resistor of 470Ω since the drop across the diode and the 5.6K pull up resistor bias - keeps Q1 from amplifying anything - it's sits idle - because the Emitter and Base difference is too low to apply power thru to the Collector - or accept a difference in power across it - the transistor Q1 is a PNP.
So for it to fire, it has to see a sag in the load which makes D4 no longer conduct thru R9 that 470Ω (ohm) , instead the transistor turns ON harder - and that Gate trigger - the divider of the Collector output of that Q1 the 100Ω (R12) and that 1KΩ (R11) - the gate fires, the SCR pulls the power down.
The last thing - which really should have been the first thing...
Replace those filter caps - the ripple smoothing they are supposed to do, gets less and less as they age - so it may not be able to filter so the 723 sees the ripple and shuts down output that way.
All cases bolted to the heat sink cannot show short to the heat sink - including the pass transistors.
To see if the system still works, just remove the SCR - if the thing never sags - then the crowbar circuit - including the SCR trigger, has to be checked.
D4 is a 5.6V Zener in that crowbar circuit. Along with R9 - forms a window of "on" operation - as long as the voltage on the positive post of the output, stays above a threshold, D4 pulls power into a limiting resistor of 470Ω since the drop across the diode and the 5.6K pull up resistor bias - keeps Q1 from amplifying anything - it's sits idle - because the Emitter and Base difference is too low to apply power thru to the Collector - or accept a difference in power across it - the transistor Q1 is a PNP.
So for it to fire, it has to see a sag in the load which makes D4 no longer conduct thru R9 that 470Ω (ohm) , instead the transistor turns ON harder - and that Gate trigger - the divider of the Collector output of that Q1 the 100Ω (R12) and that 1KΩ (R11) - the gate fires, the SCR pulls the power down.
Replace those filter caps - the ripple smoothing they are supposed to do, gets less and less as they age - so it may not be able to filter so the 723 sees the ripple and shuts down output that way.
All cases bolted to the heat sink cannot show short to the heat sink - including the pass transistors.
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Power supply update. Part RCA29 came in installed and all works great. I also added the variable mod to the supply. All astron supplies 7-10-20-35-50 amp with or without meters has the provisions on board to make the power supply variable 0-15 volts. thanks to all who replied.
Here is a link on my server with a short video of the mod i did.
Only problem was cutting the hole out for the meter. the metal was quite thick and had to do a lot of filing to fit the meter.
click here
Here is a link on my server with a short video of the mod i did.
Only problem was cutting the hole out for the meter. the metal was quite thick and had to do a lot of filing to fit the meter.
click here
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