Need some input on Dim bulb tester behavior
- Thread starter Donguri
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- dbt drifting bias hk 560 hk560
Hi again, got caught up with work and also struggled with some components so pardon the absence.
Installed new Bourns trim pots (3386G, perfect drop in fit) for both Bias and DC offset.
Old pots flat bent flat leads was a challenge to remove though.. a dentist tool and some heated solder iron solved it in the end.
Also put in a new BC517 on the flat side down as per your recommendation.
Seem to be able to get it somewhat within spec with trim pot set to low.
However bias rises unevenly compared with the good channel, much slower, it takes like 10 min to get it up to 33mV and not stable as the other CH. Not too satisfied.
Wonder if this BC517 is a good substitute?
Maybe check Diode D408, if I understand it correctly its enough to desolder one leg and check it.
Installed new Bourns trim pots (3386G, perfect drop in fit) for both Bias and DC offset.
Old pots flat bent flat leads was a challenge to remove though.. a dentist tool and some heated solder iron solved it in the end.
Also put in a new BC517 on the flat side down as per your recommendation.
Seem to be able to get it somewhat within spec with trim pot set to low.
However bias rises unevenly compared with the good channel, much slower, it takes like 10 min to get it up to 33mV and not stable as the other CH. Not too satisfied.
Wonder if this BC517 is a good substitute?
Will try to remove and re-grease output transistors, seemed like a good idea after reading your last post, but otherwise not sure what more to do.
Maybe check Diode D408, if I understand it correctly its enough to desolder one leg and check it.
elnaldo
Lunatic Member
Hello. If you don't trust it's working OK, probably it's not OK yet.
Are there some fuse resistors that could be out pf specs? They are usually green and raised from the PCB. Some other differences between channels ? Regarding the diode, you could replace it with 3 x 1N4148 in series for a test.
Did you replace just one bias transistor (bc517) in one channel? Driver transistors also play a role, so check if those are originals or the right replacements.
Are there some fuse resistors that could be out pf specs? They are usually green and raised from the PCB. Some other differences between channels ? Regarding the diode, you could replace it with 3 x 1N4148 in series for a test.
Did you replace just one bias transistor (bc517) in one channel? Driver transistors also play a role, so check if those are originals or the right replacements.
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Well that does it, I am a complete fool...
Despite your explicit warnings about measuring things very carefully with power on I had a moment where I thought I was Superman.
Noticed that the Rail voltage was 43V (SM said 38V must be because of my 240V line here?) and was curious what voltages the Q418 had, thought that "will just make a small measurement" and ofc the probe slipped... Big flash and both 5AT fuses went. It is amazing how little it takes and I gained respect for the delicacy, will never try that again. I really see what you meant about not trying even once..
Tested again on DBT with new fuses and sure enough, bright light. Right outputs seems to have made it but the Left are toast.
Not going to give up on this.
You have been most helpful and kind, don't want to burden you with my self-inflicted stupidity but if you could just give a hint of how to move forward I would be very grateful and will try to fix this the best I can on my own.
Is the damage probably mostly made from Q418 and onwards reading the schematic left to right? (like Q422,Q424,C418, R450, R452 D404 Etc) or might there be damage before Q418?
In my stock there are some:
MJE15032G NPN
MJE15033G PNP
maybe that could replace the outputs? the wattage seems a bit less than original.
No fuse resistors, and will place an order for some 1N4148 and other possible damaged components.
Hope to be able to fix this. Lesson learned..
Despite your explicit warnings about measuring things very carefully with power on I had a moment where I thought I was Superman.
Noticed that the Rail voltage was 43V (SM said 38V must be because of my 240V line here?) and was curious what voltages the Q418 had, thought that "will just make a small measurement" and ofc the probe slipped... Big flash and both 5AT fuses went. It is amazing how little it takes and I gained respect for the delicacy, will never try that again. I really see what you meant about not trying even once..
Tested again on DBT with new fuses and sure enough, bright light. Right outputs seems to have made it but the Left are toast.
Not going to give up on this.
You have been most helpful and kind, don't want to burden you with my self-inflicted stupidity but if you could just give a hint of how to move forward I would be very grateful and will try to fix this the best I can on my own.
Is the damage probably mostly made from Q418 and onwards reading the schematic left to right? (like Q422,Q424,C418, R450, R452 D404 Etc) or might there be damage before Q418?
In my stock there are some:
MJE15032G NPN
MJE15033G PNP
maybe that could replace the outputs? the wattage seems a bit less than original.
No fuse resistors, and will place an order for some 1N4148 and other possible damaged components.
Hope to be able to fix this. Lesson learned..
elnaldo
Lunatic Member
Hello. Take it easy. We all have been there (and not too long ago..) I've shorted a transistor in an expensive unit last month (capacitors remained charged with near 40V after power off) Fortunately it was just a spark and no parts were damaged.
If you shorted Q418, big chances that the only part damaged is Q418, and perhaps some resistor directly connected to it. I'd check the resistors, and replace just Q418 (or both drivers, if you are using replacement transistors)
The 15032 are a bit big for drivers, but they will work. They should work for the output. Not sure about the output power of your unit, but they work fine in low powered amplifiers (installed 2 pairs in a Sansui A40 last week)
I use BD139 and BD140 for drivers in small amps.
If you shorted Q418, big chances that the only part damaged is Q418, and perhaps some resistor directly connected to it. I'd check the resistors, and replace just Q418 (or both drivers, if you are using replacement transistors)
The 15032 are a bit big for drivers, but they will work. They should work for the output. Not sure about the output power of your unit, but they work fine in low powered amplifiers (installed 2 pairs in a Sansui A40 last week)
I use BD139 and BD140 for drivers in small amps.
Hello, Thanks for the encouragement! Was quite discouraged but guess it is one of those thing you have to tackle, glad that in your case it only was sparks.
At a short preliminary check it does seem like one or both of the left outputs are shorted (makes continuity beep).
Will dive into it more next week.
This receiver is 40 watt, however it is a high current receiver so my amateur guess is that it is why they used more powerful Output transistors @ 80 watts:
2SD588A (R)
2SB618A (R)
After some research the following would've been best replacement but the second is discontinued unfortunately:
FJP1943RTU
FJP5200RTU (discontinued)
So found another thread were last post mentions these TO-3P as a good replacement:
https://audiokarma.org/forums/index.php?threads/pioneer-sa-9500ii-bias-issue.956836/#post-14750652
NJW0281G
NJW0302G
These are @ 150W but would that cause any problems or would the unit only use the wattage its designed to?
At a short preliminary check it does seem like one or both of the left outputs are shorted (makes continuity beep).
Will dive into it more next week.
This receiver is 40 watt, however it is a high current receiver so my amateur guess is that it is why they used more powerful Output transistors @ 80 watts:
2SD588A (R)
2SB618A (R)
After some research the following would've been best replacement but the second is discontinued unfortunately:
FJP1943RTU
FJP5200RTU (discontinued)
So found another thread were last post mentions these TO-3P as a good replacement:
https://audiokarma.org/forums/index.php?threads/pioneer-sa-9500ii-bias-issue.956836/#post-14750652
NJW0281G
NJW0302G
These are @ 150W but would that cause any problems or would the unit only use the wattage its designed to?
I started watching this thread because I have a receiver that exhibited similar DBT behavior.
It has become a fascinating read, and I admire your perseverance and elnaldo's willingness to help.
I looked up your unit, and it's a beautiful receiver! Hope you're able to resolve the issue.
It has become a fascinating read, and I admire your perseverance and elnaldo's willingness to help.
I looked up your unit, and it's a beautiful receiver! Hope you're able to resolve the issue.
Hello, thank you for comments, really appreciate it! And am happy that this thread add some value to someone.
Yes his guiding hand and patience has been invaluable and hope that I can pull this one through to honor that.
Couldn't find any info on this DBT behavior but it seems like in this case it is bc of a "soft start" as @mbz explained early on, hopefully it can give a hint of your case too.
Oh, yes they were, charting new territories in searching for transistors, somewhat confusing.
2sa1943
2sa5200--->2sc5200?
They are also rated @ 150W so it is of no concern for the receiver?
elnaldo
Lunatic Member
You are right, 2sa1943 & 2sc5200 is the pair. Not 2sa5200 (that's a typo)
This is one of the most known and falsified power transistors, so get them from a reputable source.
I'll check the datasheets. You usually want the ft (transition freq) close to the originals. Going up in Wattage is not a problem.
Edited: I see the originals are "batwings" case. The to3-p will be too large. I'd try to find some to-220 transistors.
This is one of the most known and falsified power transistors, so get them from a reputable source.
I'll check the datasheets. You usually want the ft (transition freq) close to the originals. Going up in Wattage is not a problem.
Edited: I see the originals are "batwings" case. The to3-p will be too large. I'd try to find some to-220 transistors.
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elnaldo
Lunatic Member
I've used mje15032 and 033 in small amps. But there are several threads here at AK about replacing your original transistors.
I'd say that the 15032, being 8A and 50W parts should work. Ft is higher so there is a chance of some oscillation, but that can be solved later with a small capacitor if it happens (never happened to me, but it's possible)
Also, Tip41C could work if your rail voltages are near 40V, since the CE voltage is 100V instead of 150V of the originals. You want a transistor that can hold the full voltage from +V to -V in case of a problem.
Mje15032 and the Tip are not as linear as the jrp5200 (check the gain/current graphs, you'll see the gain starts to drop after 2A current, not in the 5200, it has a flat gain well after 5A). But they served well to hundreds of thousands of amplifiers around the world, so I use them in small amps.
I'd say that the 15032, being 8A and 50W parts should work. Ft is higher so there is a chance of some oscillation, but that can be solved later with a small capacitor if it happens (never happened to me, but it's possible)
Also, Tip41C could work if your rail voltages are near 40V, since the CE voltage is 100V instead of 150V of the originals. You want a transistor that can hold the full voltage from +V to -V in case of a problem.
Mje15032 and the Tip are not as linear as the jrp5200 (check the gain/current graphs, you'll see the gain starts to drop after 2A current, not in the 5200, it has a flat gain well after 5A). But they served well to hundreds of thousands of amplifiers around the world, so I use them in small amps.
Saw your edit now,
Yes they are bat winged but read somewhere that it''s possible to use the old ones to hold down replacements to the heat sink, but maybe they didn't mean the To3-P? Would they be too big for even that?
Edit: saw the extensive last post,
Thinking I could try the mje15032 and 033 for now and maybe order the to3-P just to see if it''s possible?
Yes they are bat winged but read somewhere that it''s possible to use the old ones to hold down replacements to the heat sink, but maybe they didn't mean the To3-P? Would they be too big for even that?
Edit: saw the extensive last post,
Thinking I could try the mje15032 and 033 for now and maybe order the to3-P just to see if it''s possible?
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Hello again, working slow but just wanted to give an update.
Have a new nemesis: 90 degrees Flat bent leads.. Took a while to get the Lch outputs out.
Q422: 2sd588A is toast
Q424: 2sb618A is also toast.
Took a chance on a defect unit with the non A version of the outputs that I want to try, should be here end of the week.
They have almost identical specs except VCE seems a little bit less, hope this sounds like a good idea.
R450 measures fine at 100 ohm.
C418 measures fine at 1 uf.
Q418 driver: 2SD667A measures 1.5 volt between E to C probably bad.
Q420 driver: 2SB647A makes continuity beep so probably bad.
Emitter resistors seems ok comparing between channels in ohm setting.
Found originals to the Drivers at a place called BDent, would it be a good idea to buy those?
It is OK if it cost a little as I see it as an investment on the path of learning.
Otherwise it was suggested in one thread that these could be used:
2SD667A -> KSC2383YTA
2SB647A -> KSA1013YTA, not sure if these are suitable or maybe even better than the originals?
Have a new nemesis: 90 degrees Flat bent leads.. Took a while to get the Lch outputs out.
Q422: 2sd588A is toast
Q424: 2sb618A is also toast.
Took a chance on a defect unit with the non A version of the outputs that I want to try, should be here end of the week.
They have almost identical specs except VCE seems a little bit less, hope this sounds like a good idea.
R450 measures fine at 100 ohm.
C418 measures fine at 1 uf.
Q418 driver: 2SD667A measures 1.5 volt between E to C probably bad.
Q420 driver: 2SB647A makes continuity beep so probably bad.
Emitter resistors seems ok comparing between channels in ohm setting.
Found originals to the Drivers at a place called BDent, would it be a good idea to buy those?
It is OK if it cost a little as I see it as an investment on the path of learning.
Otherwise it was suggested in one thread that these could be used:
2SD667A -> KSC2383YTA
2SB647A -> KSA1013YTA, not sure if these are suitable or maybe even better than the originals?