Topward 6303A power supply (again)

[saturated]

In summary the left side won't get past about thirteen volts
But the other day it started working and working really good. Relays clicking like gangbusters    As in I turned it to almost thirty volts and it held steady. 


Then it went back to messing up again 

Do you think it worthwhile to replace these capacitors

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However seems kind of pointless to ask I know this is not proper form to blindly start replacing stuff.

And to be fair up to this point I was like "dude it's a bad relay"

  

[dmeek]

Could be an open main filter capacitor. Check for ripple if you have a scope, otherwise
check DC or AC voltage across each cap.

The schematic for the 6303DS is here, maybe similar
https://www.radiomuseum.org/r/topward_el_dc_power_supply_6303ds.html

A bit of an ordeal to download but at least it's available.

[saturated]

Thank you sir 

I did open it up and take a few measurements per your suggestions

I get about (plus or minus) DC readings

Left side
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Right side I think it said C28 before I flipped the board over

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Repeating in ac volts not much

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But idk about the AC volts because this is with the probes not connected to anything 

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I have a scope and I like to use it but not sure where to probe and maybe these measurements are enough to draw a conclusion...idk.

Seems from the DC measurements the caps are functioning 

[saturated]

Ok sorry they are C22 and C23 and polarity is marked (duh) 

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[dmeek]

I see from the schematic the relays switch transformer secondary taps for the unregulated DC on C23 and C22. Bad relay contacts seem more likely. Does the output voltage jump if
you tap the relays with a screwdriver handle?


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[saturated]

Thank you sir I will definitely give that a try this evening   

[dmeek]

Here is the rest of the schematic except for the meters. 
If you're not hearing relays clicking while turning
the Voltage knobs, try tapping the circuit boards in various places.
There might be a bad solder connection somewhere. 

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[saturated]

Yes sir thanks I did remove the cover power on and do some rapping on the relays and moving the boards around a little to no avail. 

But I did discover something.....

The slave voltage has full range in parallel mode 

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And stops at about ten volts in independent and series mode

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I appreciate your help I know this is pretty complicated 

It's velly intresting 

[dmeek]

Must be some kind of bad connection if it works sometimes.
Master and slave boards have 4 fuses each. Could one be blown or intermittent?
I always check/re-solder all pins of those white connectors, a common problem.
The circuit is quite complicated and the schematic is a mess too.
Hopefully a good visual check will find the problem.

[J M Fahey]

What a complex power supply 

It scratches my minimalist brain quite the wrong way.

Oh well.

[saturated]

Thank you sir it's nice to know heavy hitters like you and Mr DMeek don't take this lightly.

Btw I found this on the interwebz

https://www.eevblog.com/forum/repair/topward-6303a-repair/msg5382143/#msg5382143

I know it's ill advised to start shotgunning parts but I ordered some 2sa1015 anyway and I'm thinking about shooting on sight. 

I already have a bunch of 1815s.

And I already replaced an 1815....and surprise surprise it didn't fix it 

[g1]

Do you have freeze spray in your arsenal?  Can be very handy for finding iffy transistors, killing warts, etc.   
But I do agree with dmeek, sounds like an intermittent connection or relay.

[Tassieviking]

If you have full voltage in parallel mode then the fault would seem to be in the control circuit itself for the slave side.
It appears that the 6303A has analog meters and the 6303D has digital meters, hopefully there is not much else different between the models.
Please note that there are some errors on the schematics so don't trust it completely, it is also drawn in a confusing way and really needs to be re-drawn to make it easier to read.

My brain is not engaging in gear properly lately so I have to wait for another time to have a try at it, in the mean time have a look to see if you can see what changes from parallel mode to the other modes of control.
I think the other people trying to help are smarter then me anyway so you are in good hands here.
Cheers
Mick

EDIT:::::  I had another look at the schematic I posted and it shows the digital meter circuit on page 4 but on the Utube clip at 12min and 23 seconds you can clearly see the analog voltage and current meters like your 6303A meter
Here is a Utube vid worth looking at for you, it might help some :
https://www.youtube.com/watch?v=_dBj0VNB73Q