I can't be sure 100%, but your soldering looks a little bit messy. You can disconnect secondaries and solder on the table, two diodes and one capacitor and measure DC voltage.
TBH, I'm pretty confident with soldering, I used to do it for a living. I've checked and not found any thing remotely dry, but I've reflowed just in case.
I'll give it a go on the bench
I'll give it a go on the bench
Check the centre pin of the LV connector for a dry joint, can't think it could be anything else.
I've found the problem, it's a broken track on the positive lead of C1P. Couldn't see it before as the cap was covering it. No idea how it happened, maybe too much heat moved the pad, but easily repairable.
Waiting for replacement caps, then should hopefully be away.
Thanks for all your help Alan and Flikoman, I will post results.
Waiting for replacement caps, then should hopefully be away.
Thanks for all your help Alan and Flikoman, I will post results.
No problem. 😉
Don't have zeners 2V, but I saw that zeners with low forward voltage aren't exactly low noise etc. It is better to use green or yellow LED diode. I'm using, for the moment, green LED, but I need 0.2V higher, so I think I'll try yellow.
You can try LED too, but bare in mind, it has to be reversed, if you look at pcb. Anode goes to ADJ pin, cathode to GND.
🙄
Just finished stuffing my BB PCB. Applied LV power & measured approximately 8.6V at V1, 2 & 3 heaters. Obviously, this is way too high. Checked all component values, orientations, possible dry solder joints, etc., all appears OK. After reading about possible issues with dodgy 7805's, I replaced this, with no effect. ZD1 (2V) tests OK. LV AC in is about 10 - 0 - 10, which is a bit high, but the regulator should be able to cope. Tried 15V AC source (which should be too low), DC output from regulator was still over 8V. Seems to me like the regulator isn't working, or isn't working as it should. Any thoughts or ideas about what the problem might be would be welcome. Thanks.
8,6V with tubes out, about 8,4V with them in. Way too high, it would fry the heaters in short order.
You messed up something. Try to replace zener diode with green LED. Bare in mind, anode led goes to zener cathode if you look markings on PCB.
Very strange - sure is! ZD1P is 1N4679/TR, 2V 0.5W zener. It measures the same as a new uninstalled one. I've rechecked LV PS components for correct placement & orientation, examined solder joints & replaced C2P (which was OK). Main filter capacitor (3300uF), rectifier diodes & 7805 regulator measure OK. All PCB components are as per BOM (except LED's), so its a basic, standard build, without multi-FET boards. Haven't as yet installed (2.2uF) output caps (waiting on these) but I doubt this would affect LV PS. Also haven't tested HV PS; thought it best to sort LV first. Interestingly, relays operate when LV power is applied, S1 is on & tubes are in place, but LED's don't. I installed blue ones, however think I read somewhere that they should be red or green? I'll replace LED's with red ones & ZD1P with same or similar zener & see what happens. I see that LV power traces go to other (input) end of the PCB. Is it possible a fault there might be influencing the LV supply? Thanks again for your replies.
The LV should work without any HV present, I always test the LV first without HV.
Relays will click with S1 closed.
Leds will only light with valves operating (MM mode) so need LV and HV active.
Relays will click with S1 closed.
Leds will only light with valves operating (MM mode) so need LV and HV active.
Replacing zener with green LED fixed the problem. Now have 6.9V on V1 & V3 heaters, 5.8V on V2. Applied HV, all critical voltages are good. LD1's operate OK as do relays. I'll now add C8's & setup PCB to have a listen. Thanks to all for comments & suggestions.
5.8V is too low. Replace 2x 8R2 with 2x 4R7 resistors. Don't know the markings, I am at work, but they are close to ECC83 socket. Aim for 6.3V. If you have to, add another 5R6 in paralell to one of 4R7 later, but for now, try with 2x 4R7.
I'm afraid I'm back again.
I've sorted my original problem and now have voltage at the valves. The trouble is, not enough. With valves in, V1 is 4.97, V2, 4.37 and V3, 4.93. With valves out, all read 5.01.
DC across C1 is 13.56 with valves out, 11.2 with valves in. No AC across C1
Out pin of regulator is 5.03.
Any ideas?
I've sorted my original problem and now have voltage at the valves. The trouble is, not enough. With valves in, V1 is 4.97, V2, 4.37 and V3, 4.93. With valves out, all read 5.01.
DC across C1 is 13.56 with valves out, 11.2 with valves in. No AC across C1
Out pin of regulator is 5.03.
Any ideas?
Zener is there to "lift" Vout of 7805. Maybe you didn't solder zener the right way or something. Post pictures.
Try green led instead of zener diode, but led anode must go to cathode on PCB.
Try green led instead of zener diode, but led anode must go to cathode on PCB.
Thanks, zener is definitely the right way round.
I'll replace and try again, and also try green LED.
Won't be for a few days, as working until weekend.
I'll replace and try again, and also try green LED.
Won't be for a few days, as working until weekend.