I am not normally this stupid, but *all* of the problems I have had with this amplifier are my own fault.. When I first opened it up (years ago), it was simply to clean the variable resistor because the audio kept cutting out. It was very dumb of me to run the amplifier with the cover off (knowing it was part of the heat sink), and that is when I started to blow stuff up.
After replacing all of the Z44's I think I may have had one of the heat sink isolators move, and that blew out one of the replacement Z44's.
At some point in this, I guess those 2N640's blew up too (may have also been from the heat?).
R63 cooked when I pulled the legs on Q35-38, but left Q28-31 connected.
Going to order a fresh set of 10 Z44's (I don't remember where I got the first batch from, no idea if they are counterfeit or not). Also going to order a full set of the 2N6488 and the 2N6491 to keep them all the same. Still not clear if I should order new resistors (look like 0.22 ohm?) They all look good, and test the same with the OHM meter (although with resistance that low, who knows how accurate it is!). Still open to opinions on replacing those.
Before I place the order, do any of ye know the correct value for R63? Mine is too burnt to tell. Guessing there is a corresponding resistor in the other channel, but have not yet tried to trace it that way.
Thanks again!
After replacing all of the Z44's I think I may have had one of the heat sink isolators move, and that blew out one of the replacement Z44's.
At some point in this, I guess those 2N640's blew up too (may have also been from the heat?).
R63 cooked when I pulled the legs on Q35-38, but left Q28-31 connected.
Going to order a fresh set of 10 Z44's (I don't remember where I got the first batch from, no idea if they are counterfeit or not). Also going to order a full set of the 2N6488 and the 2N6491 to keep them all the same. Still not clear if I should order new resistors (look like 0.22 ohm?) They all look good, and test the same with the OHM meter (although with resistance that low, who knows how accurate it is!). Still open to opinions on replacing those.
Before I place the order, do any of ye know the correct value for R63? Mine is too burnt to tell. Guessing there is a corresponding resistor in the other channel, but have not yet tried to trace it that way.
Thanks again!
Attachments
R63 is 47ohms. The emmiter resistors below are nice pieces, I have purchased and used them myself.
.22 OHM 2 WATT EMITTER RESISTORS FOR PHASE LINEAR OTHERS 12 PK | eBay
.22 OHM 2 WATT EMITTER RESISTORS FOR PHASE LINEAR OTHERS 12 PK | eBay
Looks like R63 is 1/4 W?? Mouser 660-MFS1/4DCT52R47R0 should work?
Are the emitter resistors replaced as a matter of best practice? It is not that I am being cheap, but trying to avoid doing more work than needed (risk of damaging something else).. If I really should change them, would Mouser 594-AC030002207JAC00 work for this?
Hopefully the rest of these parts are correct:
10 X 942-IRFZ44NPBF
10 X 863-2N6488G
10 X 863-2N6491G
Anything else I should order while I am in there? Refresh the big capacitors?
Before replacing the PS FETs that are in it now, I'd get the output working.
As far as replacing the capacitors, I would not unless you have a good reason to do so. It's a pet peeve of mine to see perfectly good parts replaced for no reason.
The emitter resistors that you listed are the right value but you'll have to check the size. They may be larger than what you have. Yours may be OK but it's sometimes hard to read low value resistors with a standard multimeter. Measure carefully.
The last 3 parts and the 47 ohm resistor are OK.
As far as replacing the capacitors, I would not unless you have a good reason to do so. It's a pet peeve of mine to see perfectly good parts replaced for no reason.
The emitter resistors that you listed are the right value but you'll have to check the size. They may be larger than what you have. Yours may be OK but it's sometimes hard to read low value resistors with a standard multimeter. Measure carefully.
The last 3 parts and the 47 ohm resistor are OK.
Again, thanks for all the advice!
You are suggesting I not replace the Z44's? One of them is "different", and earlier in the thread I was told that one is likely counterfeit. I have 20 of those "counterfeit" parts, so I could replace the rest with them so they all match.. Although, I am not sure if they are actually "counterfeit", and how I can confirm. Plan was to order all of the parts at one time to save shipping (which is typically most of the cost).
I am going to skip replacing the resistors.. Once it is up and running, I will test the voltage drop across them to make sure they are equal.
I'll skip replacing the capacitors. Again, don't want to touch more than what is needed.
You are suggesting I not replace the Z44's? One of them is "different", and earlier in the thread I was told that one is likely counterfeit. I have 20 of those "counterfeit" parts, so I could replace the rest with them so they all match.. Although, I am not sure if they are actually "counterfeit", and how I can confirm. Plan was to order all of the parts at one time to save shipping (which is typically most of the cost).
I am going to skip replacing the resistors.. Once it is up and running, I will test the voltage drop across them to make sure they are equal.
I'll skip replacing the capacitors. Again, don't want to touch more than what is needed.
What was the source of the remaining 20?
I don't know who suggested not replacing the FETs. If you have one that doesn't match, you, at the very least, have to replace that one and the rest in that bank. All in parallel must match.
What are the test conditions going to be when testing the resistors after the amp is repaired?
I don't know who suggested not replacing the FETs. If you have one that doesn't match, you, at the very least, have to replace that one and the rest in that bank. All in parallel must match.
What are the test conditions going to be when testing the resistors after the amp is repaired?
Those are the ones from Ebay. "MiamiElectronics" was the seller.
Yup. You had said "Before replacing the PS FETs that are in it now, I'd get the output working", I guess I misunderstood.. My point was- I want to order all of the parts I think I will need in one shot. I will get 10 fresh Z44's.
Figured I would run a steady tone at a fixed level in to a regular speaker and test the voltage across the resistors.
I didn't mean not to replace them period. Just wait until you get the audio section repaired in case you might damage the FETs.
To test as described, you'll have to drive to a significant level and will need to clamp the heatsink mounted components.
How different were the readings between them with your meter?
To test as described, you'll have to drive to a significant level and will need to clamp the heatsink mounted components.
How different were the readings between them with your meter?
Identical on the OHM meter, but the probes themselves measure .1 ohm! My Fluke 83 is not that precise. I have a Fluke 189 somewhere, maybe that is better.
The REL button zeros out the leads (leads being held together when button pressed).
For future reference, It's possible to measure very low resistances, even with meters that won't do it alone. You use a secondary power source and a limiting resistor to drive current (more than a multimeter can supply) through the resistor being tested. Then you would use your meter to measure 'voltage' across the resistor being tested. You don't need to do that here. If they read the same with your fluke, they're likely OK.
For future reference, It's possible to measure very low resistances, even with meters that won't do it alone. You use a secondary power source and a limiting resistor to drive current (more than a multimeter can supply) through the resistor being tested. Then you would use your meter to measure 'voltage' across the resistor being tested. You don't need to do that here. If they read the same with your fluke, they're likely OK.
I believe it was these, though I admit I haven't looked inside it to confirm yet. This is what came up in my past mouser orders, pretty sure it's the right one.
https://www.mouser.com/datasheet/2/308/NJW3281-D-100028.pdf
Parts came in.. the 47 OHM resistors look significantly smaller than what I will be replacing (length is maybe 3mm shorter). Always thought the body size was for heat dissipation based wattage. Is the original resistor a 1/2W, and not a 1/4W? In my experience, the 6mm package size is 1/4W. Thought maybe Mouser shipped me 1/8 by mistake, but noticed the web site says the size is 3.4mm.
MFS1/4DCT52R47R0F KOA Speer | Mouser
Thanks.
MFS1/4DCT52R47R0F KOA Speer | Mouser
Thanks.
Ok, all the parts are installed. Amplifier is back together. Powered it on, music playing on both channels.. Success?? Not sure yet..
As I turn the current limit up on the power supply, it continues to draw all the power supply will deliver. Volume is VERY low, so I don't think that is right.
I think I changed them a few years back when I installed the Z44's..
As I turn the current limit up on the power supply, it continues to draw all the power supply will deliver. Volume is VERY low, so I don't think that is right.
I think I changed them a few years back when I installed the Z44's..
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