Zenith DLP Set Not Working After Lamp Replacement
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From: Franc Zabkar on 9 Aug 2008 19:05 On Sat, 9 Aug 2008 19:42:00 -0700, "Chris F." <zappyman(a)hotmail.com> put finger to keyboard and composed: >> BTW, are you posting from Canada, as your IP suggests, in which case >> how are you expecting to get 400VDC from a 120VAC supply ... assuming >> your circuit is similar to the one I have posted? I'm posting from >> Australia where the mains is 240VAC, BTW. Does your PSU have a voltage >> doubler section at or near the bridge rectifier (D801)??? Is there a >> connection between the neutral conductor and the midpoint of two bulk >> caps??? If there is no voltage doubler, can the E1017 IC boost the >> supply from 160V to 400V via T801??? If so, then you may want to check >> R810 and R811 for OC. BTW, the notes around T830 indicate that there >> are North American and "domestic" versions of this SM transformer, so >> this would suggest that the PSU circuit applies universally. In fact >> the Australian manual states that the acceptable input voltage range >> is 110VAC-240VAC (10%) at 50/60 Hz. So maybe IC810 performs PFC *and* >> voltage doubling??? > > In my case, it does appear that IC810 also performs some kind of >voltage-doubling, via T801. There are no other components to do the job, in >fact the circuit appears to perfectly match the schematic you provided me. > I've since tried injecting 400V from an external power supply (to C820), >surprisingly it doesn't make any difference at all. While the ballast now >gets the correct 400VDC, the output voltages in the low voltage supply are >still down by more than 50%. What's more, the "replace lamp" light is still >blinking. I'm more confused than ever now. > I'm only using that basic schematic you sent me first - I haven't been >able to download the rest because eserviceinfo is not responding today. >Maybe I need a break from this anyway. > I guess a tech should never assume a blown lamp is just a blown lamp, when >working on junk like this..... Would an overload on the secondary side cause IC810 to shut off its PFC and voltage doubling function? Maybe you should try unloading some of the secondaries, eg the sound circuit. Otherwise you may want to check what IC830 and IC851 are doing. I would expect that, because the secondary outputs are low, this should cause the optocoupler's diode to be driven hard, which should in turn mean that pin 4 should be close to ground. This should at least prove whether the voltage feedback is working. I would then check R837. This resistor determines the current limit of your circuit. IC810 could be reducing the drive to Q830 in response to an overload on the secondaries which it would sense via R837. - Franc Zabkar -- Please remove one 'i' from my address when replying by email.
From: Franc Zabkar on 9 Aug 2008 20:46 On Sun, 10 Aug 2008 09:05:24 +1000, Franc Zabkar <fzabkar(a)iinternode.on.net> put finger to keyboard and composed: >Otherwise you may want to check what IC830 and IC851 are doing. I >would expect that, because the secondary outputs are low, this should >cause the optocoupler's diode to be driven hard, which should in turn >mean that pin 4 should be close to ground. Oops, it should be the other way around. The diode will *not* be driven, in which case pin 4 should be high. - Franc Zabkar -- Please remove one 'i' from my address when replying by email.
From: Franc Zabkar on 9 Aug 2008 21:07 On Sat, 9 Aug 2008 19:42:00 -0700, "Chris F." <zappyman(a)hotmail.com> put finger to keyboard and composed: > In my case, it does appear that IC810 also performs some kind of >voltage-doubling, via T801. There are no other components to do the job, in >fact the circuit appears to perfectly match the schematic you provided me. > I've since tried injecting 400V from an external power supply (to C820), >surprisingly it doesn't make any difference at all. While the ballast now >gets the correct 400VDC, the output voltages in the low voltage supply are >still down by more than 50%. What's more, the "replace lamp" light is still >blinking. I'm more confused than ever now. > I'm only using that basic schematic you sent me first - I haven't been >able to download the rest because eserviceinfo is not responding today. >Maybe I need a break from this anyway. > I guess a tech should never assume a blown lamp is just a blown lamp, when >working on junk like this..... Doh, I just realised that your set is behaving as if it is in standby mode. Notice the "POWER ON" signal at pin 1 and the ST-5.5V rail at pin 2 of PB41 which goes to the Tuner Board. I suspect that if you disconnect PB41 and short pin 1 & 2, the PSU will power up. I would take care when doing this because disconnecting PB41 also removes power to the fan. - Franc Zabkar -- Please remove one 'i' from my address when replying by email.
From: Chris F. on 10 Aug 2008 15:51 You're right, and I should have realized that a long time ago. Shorting those pins did power the PSU and all voltages are now normal, but the lamp still does not come on. I guess the next step is to test the ballast, but for that I need the pinout, and eserviceinfo is still down....... "Franc Zabkar" <fzabkar(a)iinternode.on.net> wrote in message news:j3fs9412vm4i0v6sk6ltnnm857k6hcvgfr(a)4ax.com... > On Sat, 9 Aug 2008 19:42:00 -0700, "Chris F." <zappyman(a)hotmail.com> > put finger to keyboard and composed: > >> In my case, it does appear that IC810 also performs some kind of >>voltage-doubling, via T801. There are no other components to do the job, >>in >>fact the circuit appears to perfectly match the schematic you provided me. >> I've since tried injecting 400V from an external power supply (to C820), >>surprisingly it doesn't make any difference at all. While the ballast now >>gets the correct 400VDC, the output voltages in the low voltage supply are >>still down by more than 50%. What's more, the "replace lamp" light is >>still >>blinking. I'm more confused than ever now. >> I'm only using that basic schematic you sent me first - I haven't been >>able to download the rest because eserviceinfo is not responding today. >>Maybe I need a break from this anyway. >> I guess a tech should never assume a blown lamp is just a blown lamp, >> when >>working on junk like this..... > > Doh, I just realised that your set is behaving as if it is in standby > mode. Notice the "POWER ON" signal at pin 1 and the ST-5.5V rail at > pin 2 of PB41 which goes to the Tuner Board. I suspect that if you > disconnect PB41 and short pin 1 & 2, the PSU will power up. > > I would take care when doing this because disconnecting PB41 also > removes power to the fan. > > - Franc Zabkar > -- > Please remove one 'i' from my address when replying by email.
From: Franc Zabkar on 10 Aug 2008 16:52
On Sun, 10 Aug 2008 12:51:46 -0700, "Chris F." <zappyman(a)hotmail.com> put finger to keyboard and composed: >You're right, and I should have realized that a long time ago. I was thrown by the fact that all the voltages were at 40%. You would normally expect that all rails would be at 0V apart from a single standby supply. >Shorting those pins did power the PSU and all voltages are now normal ... If the ballast supply is now at 400V, then this would imply that the PFC and voltage doubling function of IC810 is turned off in standby mode and turned on in run mode. This begs the question, how does IC810 know that the set is in standby mode? Perhaps this is the function of pin 5? >... but the lamp still does not come on. The uP on the Tuner Board appears to control and sense the lamp via connector P10. BTW, when you shorted pins 1&2 of PB41, I hope you removed the connector, otherwise one of the uP pins would have been subjected to 16V. >I guess the next step is to test the ballast, but >for that I need the pinout, and eserviceinfo is still down....... I have uploaded tuner PCB circuit 2-of-2 to my web space: http://www.users.on.net/~fzabkar/MB-042C/ It seems to me that if you can't get the set to come out of standby, then the M37151 uP (IC1) may be faulty, in which case your lamp problem may be a secondary issue, if it is in fact a problem at all. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |