[samplesj]

Will a backward heater diode hurt anything else on the board?

Somehow I managed to put both of the 2 diodes on the far edge pointing the same way.  Still not sure how I missed that, but I did.  Of course on power up no led color at all (not red or green).  The big tx also buzzed lightly.  It took me a few seconds to find the problem since I was distracted with the led not lighting and checking it.  Basically until the diode started smoking just a bit to draw attention to itself I didn't notice the problem.  Luckily I had 4 extras (I ordered enough to replace the higher rated ones I had on the clarinet board when I tried the 3-in-1, but didn't bother to replace them).  I replace the one that was backward and it all powered up fine.  The light was red and then green.  All of the B+ voltage were within +5%.  However the heater voltage was only 5.62.  On the other side of the big 3.0 ohm 5 watt resistor it was 7.3.  I know I can just switch out the resistor and I'll have the proper 6.2-6.3, but is it low because on of the other diodes or other components is damaged and I need to replace more?  If something else is damaged I didn't want to mask the problem by switching the resistor.

I did go ahead and hook it up to my cheap system in the bonus room as a test and it works fine.  I couldn't resist and tested it with the Maggies too.  Even with the lower H+ voltage I don't think I'm missing anything replacing the Benchmark Dac1 with the Chime.  I'll wait for more commentary until I make sure its running 100% and post some pictures like I did with my clarinet.

[hagtech]

Did you replace all of the diodes?  Are you using the schottky types?  Traces ok?  I'd be suprised if you damaged the tranny.  The small parts always smoke first.

I'd change the other diodes first.  See if the heater voltage comes back up.  If not, then try lowering the 3 ohm.  But that only means something is amiss.  Is ac line votage ok? 

jh

[samplesj]

Did you replace all of the diodes?  Are you using the schottky types?  Traces ok?  I'd be suprised if you damaged the tranny.  The small parts always smoke first.

I'd change the other diodes first.  See if the heater voltage comes back up.  If not, then try lowering the 3 ohm.  But that only means something is amiss.  Is ac line votage ok? 

jh

The diodes are the spec'd part.  I just happened to order 4 more because on my clarinet board I jumped their amp capacity up for the 3-in-1.  I was going to replace them there, but didn't want to risk damaging the traces so left the big ones on it which left 4 spare ones.

I did not replace the other three diodes.  I was trying to not have to take it all apart (I could reach the outer one with my iron), but I'll pull it back out of the case if they might be causing a problem.  I usually get around 120-124V ac out of the wall.  I'll double check that at the power input too.  The B+ voltages are pretty close, and the hagdac +/- 8 are pretty close [my good meter died sometime between my last project and this one so I'm using a cheap wal-mart special that I don't trust to be really accurate].

I'm just finishing up the cornet2 so after I finish testing it I'll change out the chime diodes.

I did have to desolder a jumper from the clarinet board in the heater resistor holes when I took apart the 3-in-1.  Until you mentioned that I didn't think about a "bad" trace/solder joint causing extra resistance.  I'll check it too.

Thanks for the help with what to check next.

[samplesj]

Hmmm, which to trust........  My cheapie meter or the cheap yaego 5w resistor markings?

The power was off earlier today so I had some time when I couldn't work and managed to finish up my Cornet2.  I just tested its heater voltages and they were low too.  I didn't smoke any parts on that board.  So I decided to just measure from lead to lead on the 5w heater resistor.  It read 2.1ohms. 

I then checked the Chime's heater resistor.  It is marked 3.0, but it reads 3.2.  Even with the meter touching the metal trace rings and not the resistor it reads 3.2 so it appears solded in ok.  I pulled an extra 3.0 out of the spares box and measured with leads hooked around the tips it read 3.2 too. 

I've got tons of extra 5watt resistors so I could tweak the combo box so I was able to find resistors that "match" the specs even though the markings are different.  They are all reading high.  Since they all read high it makes me doubt the meter.  Unfortunately I only have an ultra cheapie meter.  I didn't realize my good meter was dead until I tried to use it for this.  I've got to run to town so I'll probably break down and buy a good meter just to double check.

I could also switch one out and see if that makes the voltages come up.

What is funny is that the clarinet heater voltages were pretty much dead on.  I just got lucky with that resistor I guess.  If it wasn't for the different switches and extra remote board I'd take it apart, but the ir receiver is just barely long enough and I have to fidde with it everytime I take the bottom lid off.

[dnewman]

What does your meter read (on the Ohm) scale when you touch the
two leads together?  It's quite likely that you're seeing two effects: the
resistor is not bang on 3.0 and is instead 3.0+something within the 5%
tolerance, AND your meter is in need of calibration.  (And calibration errors
are especially noticeable in the low resistance range.)

[samplesj]

Yeah the meter is around .1 off when it should be zero.  I still haven't replaced the diodes on the chime board because I had the station in a bad place and moved too far for the cord and it caused me to drop the iron.  It hit my leg slightly on the way down, but it also tore loose the power to the heater inside.  Boy am I glad I was wearing jeans.  I tried to repair it, but its too small and there isn't really any slack.  I did pick up another cheapie pencil iron, but it doesn't want to get hot enough to desolder quickly so I'm going to wait till my replacement iron for the station is here.

I did replace the cornet2 heater resistor.  It reads fine now (after I replaced a bum tube too).  I'll have to take a few pictures for a new thread for it later.

Hopefull I'll have a new iron by Wednesday.  A few days break might be a good thing anyway so I can take care of some other projects and don't feel so pressured to get this done fast.

[samplesj]

Well I didn't get the iron until today.  I tried last Sunday with a "toy" iron from Radio shack, but it was just frustrating because I couldn't properly melt the solder.

I order several new diodes just to be sure.  With the new iron I was able to pull all the 10k caps and diodes (to have a clear workspace).  Its amazing how quickly I can melt and suck up the solder when I can turn the iron up a bit .  I did mess up the trace to the outermost one (probably the constant manipulation and heat from the other iron).  I was ready to add a jumper wire from the end of the diode to the led circuit, but it turns out I didn't actually break the trace, but just lifted it some.  With the new diodes it all worked perfectly.  Actually I had a bit of excitement with the first measurement because I was reading good H+ and good B+, but the +/-8v for the hagdac weren't valid.  I was actually taking the board off the chassis when it occured to me that I hadn't hooked up the L+/N+ to feed that transformer.

I'm reading a bit high on the B+, but I'm using a JJ GZ34 (5AR4) instead of the 5Y3.  I'll end up listening to the Sovtek 5Y3 I've got, but with both my Clarinet and Cornet I've preferred the JJ GZ34 (over sovtek 5Y3 and 5AR4).

Thanks to Jim for the troubleshooting tips and another great kit.