HomerJSimpson
Addicted Member
Have a Hafler dh-220 with shorted outputs.
what are the proper replacements?
what are the proper replacements?
Hafler dh-220
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HomerJSimpson
Addicted Member
Yes, tested out of circuit.
BUZ900 or 901, and BUZ905 or 906. (AFAIK these are made by Semelab)
Semelab ALF08N16K ALF08P16K
Exicon EC10N20 and EC10P20 https://www.profusionplc.com/type/lateral-mosfet
I believe Semelab and Exicon were licensed by Hitachi to manufacture.
They should be matched
Semelab ALF08N16K ALF08P16K
Exicon EC10N20 and EC10P20 https://www.profusionplc.com/type/lateral-mosfet
I believe Semelab and Exicon were licensed by Hitachi to manufacture.
They should be matched
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HomerJSimpson
Addicted Member
Well after doing some research these test differently than normal outputs. I believe these are actually good.
however the bridge rectifier is shorted.
however the bridge rectifier is shorted.
They are an FET with a gate, source and drain. Of course they test differently than a BJT with Base, Collector and Emitter, they are a different device. They're easy to test to see if they turn on, and off. But a shorted Bridge rectifier certainly will give you lots of trouble. They're a 25 AMP and it takes a lot to toast one. I'd be trying to find out WHY it toasted before just tossing another one in. Make sure the damper capacitor is good too. If it's bad, you'll toast the new one in short order because it will "ring" (not audibly). It's the ceramic disc that goes across the 2 AC terminals.
HomerJSimpson
Addicted Member
Got the new bridge rectifier and installed it.
On the DBT it powers up but the build is lit, but not at full brightness.
Is this one of those amps you cant power up on a dbt?
On the DBT it powers up but the build is lit, but not at full brightness.
Is this one of those amps you cant power up on a dbt?
no..
HomerJSimpson
Addicted Member
Well it works and makes sound on the dim bulb tester.
Adjust bias trimmers to min.See if the build dims down.
HomerJSimpson
Addicted Member
How do I adjust the bias?
Racingh11
Super Member
You adjust P2, and I'm guessing... while you measure voltage across R33. Should be somewhere from .4 to .75V
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Page 11 of the manual has the bias adjustment procedure. It is measured by measuring the B+ current with an ammeter for 275ma.
No, you pull the B+ fuse for each channel and directly measure the current with a meter set to Amps (first), then if it is lower than the mA fuse rating in your meter, switch to mA configuration for final adjustments. Clip leads are a MUST for this procedure because of where the fuse holders are located. I took some old BLOWN fuses and soldered L-shaped leads to them just for this purpose. Plus I keep spare fuses on hand for all my meters, especially the expensive
Fluke fuses.What wattage bulb? A 60w will glow pretty good since the BIAS current is (factory spec) at 275 mA per channel. Most people bump it up to over 300 mA, but the outputs run HOT.
Racingh11
Super Member
Well, it was a solid guess. There are other amps that use that same output design and are set that way, but I would say the amperage method would be more accurate since MOSFET gate-source voltages can vary slightly.No, you pull the B+ fuse for each channel and directly measure the current with a meter set to Amps (first), then if it is lower than the mA fuse rating in your meter, switch to mA configuration for final adjustments. Clip leads are a MUST for this procedure because of where the fuse holders are located. I took some old BLOWN fuses and soldered L-shaped leads to them just for this purpose. Plus I keep spare fuses on hand for all my meters, especially the expensive
You need a meter that will measure AMPS (current) and know how to set it up to read it. Most require switching leads around to configure them. Take note of the (fused) ports on the meter because it is easy to blow the fuses internal to the meter. If that happens, you're "stuck" until you replace the fuse(s). Why is this? Well...
You remove the B+ fuse from whichever amp you are adjusting. (I do both at the same time). Your meter becomes the fuse and that is why you need to be careful about the internal fuse(s) of your meter. Clip your leads across the fuse clips (you do have clip leads, right?) with the black lead towards the big filter capacitors. Although it really doesn't matter, just read the numbers. A - (negative sign) means nothing here. I start with the AMPS configuration to be sure I don't blow the mA fuse. Then if all is well, switch to the mA configuration. If on the DBT, adjust BIAS to around 200 mA. Then on direct AC power, finish adjusting to 275 Ma to be at factory spec. I run mine at 300 mA and all is well.
It's all about access here. The fuses are the only "convenient" way to do it.
