i'd be checking the caps on board three for shorts or high ESR.
if the problem is showing up on other boards it may a main supply fault as in bad bridge rect.
if the problem is showing up on other boards it may a main supply fault as in bad bridge rect.
Keep it to just the one unit and problem 🙂 Things get really really confusing otherwise.
So it looks like the bias was sky high. Did you use the bulb tester ? because that should have lit brightly. Also in post #11 I mentioned,
1. Disable the vbe multiplier to reduce output stage current to zero on both channels.
Thats a good safeguard for initial testing because it forces the bias to zero (assuming no other issues are present) and allows confirmation that all is OK.
So it looks like the bias was sky high. Did you use the bulb tester ? because that should have lit brightly. Also in post #11 I mentioned,
1. Disable the vbe multiplier to reduce output stage current to zero on both channels.
Thats a good safeguard for initial testing because it forces the bias to zero (assuming no other issues are present) and allows confirmation that all is OK.
Hi,
I must admit I do not own a bulb tester or know how to disable the vbe multiplier, so I might have skipped those steps =-(
I must admit I do not own a bulb tester or know how to disable the vbe multiplier, so I might have skipped those steps =-(
While I am here what are your guys thoughts on these photos, is this glue or a bled caps?
Evidence for glue : On same caps on both boards, on the larger caps
Evidence for bleed: It is reacting with the copper rails. The glue for screws is green and the glue for the caps looks different?
Any ideas?
Evidence for glue : On same caps on both boards, on the larger caps
Evidence for bleed: It is reacting with the copper rails. The glue for screws is green and the glue for the caps looks different?
Any ideas?
I checked with Rotel.
It is glue that becomes conductive with ages (what a crap glue).
So current had been flowing through the glue precipitating crystal growth.
Time to clean off some glue!!!
It is glue that becomes conductive with ages (what a crap glue).
So current had been flowing through the glue precipitating crystal growth.
Time to clean off some glue!!!
Glue is somthing of an industry wide problem...
The Vbe multiplier can be simply shorted out as shown with a bit of wire. This removes the bias from the outout stage. A good amp will still work normally, all you might hear is a little crossover distortion at very low volume giving a "rough" sound).
The bulb tester is a 100 watt mains filament bulb in series with the live mains feed to the amp (used like a fuse)
The Vbe multiplier can be simply shorted out as shown with a bit of wire. This removes the bias from the outout stage. A good amp will still work normally, all you might hear is a little crossover distortion at very low volume giving a "rough" sound).
The bulb tester is a 100 watt mains filament bulb in series with the live mains feed to the amp (used like a fuse)
Attachments
Wish I had asked for clarification earlier, that is quite simple.
If only they still made GLS lamps. I'm sure I can find something though.
If only they still made GLS lamps. I'm sure I can find something though.
sorry for asking i thought it was a particular lamp with a specific property
are incandescent lamps no longer available in your part of the world
are incandescent lamps no longer available in your part of the world
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General Lighting Service Lamp.
Electricians have funny names for things. Why oh why we have to call bulbs lamps is beyond me.
A standard tungsten/argon bulb.
Electricians have funny names for things. Why oh why we have to call bulbs lamps is beyond me.
A standard tungsten/argon bulb.
Energy efficiency laws have kicked in, so you can no longer buy GLS.
It's kind of stupid really.
They banned the higher power ones first (for incandescent the higher the power the more efficient).
Now they allow modified halogens in low power (halogens are only efficient in high power).
Or CFL (compact flourescent lamp).
CFL are not that efficient and as no-one has hazardous disposal at home it will involve a LOT of mercury being released in to the environment.
High power lamps should be fluorescent (but they have banned them, so only allowed the smaller less efficient ones), or LED (which are just brilliant, poor pun sorry).
Yet do they recommend the LED, do they !"£$.
It is silly one of my friends had to exchange hundreds of 6' florescent (which are really efficient) for 5' as they use less power (but produce even less light).
So basically a supermarket had to spend tens of thousands to make their lighting less efficient to comply with efficiency laws! Absolutely ridiculous, but at least it keeps my friends busy.
It's kind of stupid really.
They banned the higher power ones first (for incandescent the higher the power the more efficient).
Now they allow modified halogens in low power (halogens are only efficient in high power).
Or CFL (compact flourescent lamp).
CFL are not that efficient and as no-one has hazardous disposal at home it will involve a LOT of mercury being released in to the environment.
High power lamps should be fluorescent (but they have banned them, so only allowed the smaller less efficient ones), or LED (which are just brilliant, poor pun sorry).
Yet do they recommend the LED, do they !"£$.
It is silly one of my friends had to exchange hundreds of 6' florescent (which are really efficient) for 5' as they use less power (but produce even less light).
So basically a supermarket had to spend tens of thousands to make their lighting less efficient to comply with efficiency laws! Absolutely ridiculous, but at least it keeps my friends busy.
maybe i can send you a christmas care package 60 or 100 watt?or 7 watt mogul base red and green x-mas jobbies...
I have some GREAT issuses with those "intelligent" people who made it illegal to produce and use GLS-lamps.
For what is it we have got instead of theese harmless incadence lamps?
Lamps filled with mercury, wich demands special waste treatment with more trucks driving around for to pick them up whenever those lamps is thrown away.
Possibly more mercuyr in the nature due to most peoples rather careless handling of such lamps, intentionally or not.
And here in the COLD north (Some minus 10°C here now) the energy saving lamps have trouble lighting up where mounted outdoors, and the missing heat from the incadence lamps inside has to be provided by more power via the radiators anyway.
NO real power saving,
HEAVIER load to the enviroment.
Thanks a lot Enviromentalists behind this IDIOTIC banning of incedence lamps.
For me the only toruble is the fact that there is already much more difficult to get scalelamps for all vintage radios with incadence lamps to lighten up scales and indicators.
And LED is a rather poor replacement.
Well, there went a lot of steam.
For what is it we have got instead of theese harmless incadence lamps?
Lamps filled with mercury, wich demands special waste treatment with more trucks driving around for to pick them up whenever those lamps is thrown away.
Possibly more mercuyr in the nature due to most peoples rather careless handling of such lamps, intentionally or not.
And here in the COLD north (Some minus 10°C here now) the energy saving lamps have trouble lighting up where mounted outdoors, and the missing heat from the incadence lamps inside has to be provided by more power via the radiators anyway.
NO real power saving,
HEAVIER load to the enviroment.
Thanks a lot Enviromentalists behind this IDIOTIC banning of incedence lamps.
For me the only toruble is the fact that there is already much more difficult to get scalelamps for all vintage radios with incadence lamps to lighten up scales and indicators.
And LED is a rather poor replacement.
Well, there went a lot of steam.
For cold temps LEDs are even better, the colder you run them, the more efficient they get.
There is a HUGE difference in efficiencies though.
You need to be buying cutting edge.
The old luxeon 3W LEDs put out about 90 lumens and were very fragile.
The current Cree 3W put out over 500 and are reliable.
Buy some Cree LEDs, buy a separate driver (get a good one) and you have an efficient powerful light.
There is a HUGE difference in efficiencies though.
You need to be buying cutting edge.
The old luxeon 3W LEDs put out about 90 lumens and were very fragile.
The current Cree 3W put out over 500 and are reliable.
Buy some Cree LEDs, buy a separate driver (get a good one) and you have an efficient powerful light.
To get back on topic.
The RB-993 is now working fine (and will hopefully stay that way).
The right channel of the RB-991 is silent....
What things can I be checking with only a multimeter?
The RB-993 is now working fine (and will hopefully stay that way).
The right channel of the RB-991 is silent....
What things can I be checking with only a multimeter?
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