Hello All,
I should have turned the Hafler P1500 amp off before connecting speakers but I didn't. 2 speaker wires shorted, sparks, etc., now the amp does not work. Where do I start to get it working again?
I can solder and I have a multimeter. I am not an electronics guy but am eager to learn.
Thanks in advance for your help and Happy Holidays!
Bill
I should have turned the Hafler P1500 amp off before connecting speakers but I didn't. 2 speaker wires shorted, sparks, etc., now the amp does not work. Where do I start to get it working again?
I can solder and I have a multimeter. I am not an electronics guy but am eager to learn.
Thanks in advance for your help and Happy Holidays!
Bill
Wow, sorry to hear that! Well, to get you started (and me, as this is my first post on this forum!)....check the fuse. If you are lucky (very) it will have blown - replace and try amp. You didn't say if it powered on or not...just that "amp does not work". More description = easier to diagnose.
If it's not the fuse, go online and try to find the service manual/schematic for the amp. Cuz you'll be opening it up. Possible problems? Blown output transistors/FETs and associated components. Possibly there was a protection device in there that blew like a fuse to protect things - the schematic would tell you/us if there's something in there...
Hopefully it is 'service friendly' rather than SMD, which are a bit harder to work on.
Good luck!
If it's not the fuse, go online and try to find the service manual/schematic for the amp. Cuz you'll be opening it up. Possible problems? Blown output transistors/FETs and associated components. Possibly there was a protection device in there that blew like a fuse to protect things - the schematic would tell you/us if there's something in there...
Hopefully it is 'service friendly' rather than SMD, which are a bit harder to work on.
Good luck!
Welcome, now before you start trying to solve things and waste money blowing up new part or giving yourself a shock or 2... looking on line for info to the untrained leaner can be wasting time.
cold check parts is straight forwards select your meter to buzz or diode this will show you if there's damaged part's such as large out transistors etc. these are npn and pnp pairs then you have driver transistors then check it's bias circuit right back to the input pairs..
set up a 60w or 100w bulb at the mains 240 ac in this will glow bright show mass shorts ie it acts like a limiter. normal work amps the bulb glows then fades.
anyhow good luck with things
cold check parts is straight forwards select your meter to buzz or diode this will show you if there's damaged part's such as large out transistors etc. these are npn and pnp pairs then you have driver transistors then check it's bias circuit right back to the input pairs..
set up a 60w or 100w bulb at the mains 240 ac in this will glow bright show mass shorts ie it acts like a limiter. normal work amps the bulb glows then fades.
anyhow good luck with things
It is MOSFET design as I know, sources coupled to ground and floating transformer. Most likely blown MOSFET + fuse.
Hey Overall, amptech, Gibson GM:
thanks for the tips. Sorry about the vague description beforehand. Here's what I now know:
Fuse is intact
Channel 1 has low audio output, treble frequencies only.
Channel 2 has 0 audio output.
I have the manual and schematic. I'm eager to "cold check" parts but know nothing about "buzz" or "diode" setting on the multimeter. I have attached a phone of my meter. Please, if you would, tell me how to set it for the cold check and let me know what it should read.
My dad designed oscilliscopes for a living but I never did much with electronics (he did teach me how to solder), but now I'd love to use this opportunity to learn and save $$$.
Thanks!
Attachments
Start on e-bay. 😀 Actually, have you checked all the internal fuses too?
Did only one channel get shorted? If so and and both sound messed up, I would suspect power supply internal fuses or if this unit has any shared protection circuits.
If they still were using the Toshiba MOSFTES, they are not available, so one has to convert to Exicon. This is not s simple substitution. It requires circuit redesign.
I also found in my DH-120 that when I blew outputs, I usually took a lot of the VAS out.
Troubleshooting a feedback circuit is not a trivial task. Even if you found shorted outputs, just changing them won't fix the amp. Do you know how to read a schematic?
Not good news, sorry.
PS: designed scopes eh? Whose I might ask? I was a tech for many years and used a great many.
Did only one channel get shorted? If so and and both sound messed up, I would suspect power supply internal fuses or if this unit has any shared protection circuits.
If they still were using the Toshiba MOSFTES, they are not available, so one has to convert to Exicon. This is not s simple substitution. It requires circuit redesign.
I also found in my DH-120 that when I blew outputs, I usually took a lot of the VAS out.
Troubleshooting a feedback circuit is not a trivial task. Even if you found shorted outputs, just changing them won't fix the amp. Do you know how to read a schematic?
Not good news, sorry.
PS: designed scopes eh? Whose I might ask? I was a tech for many years and used a great many.
Thanks a zillion for the info. One channel is gone, the other sounds like it's coming through a telephone. I don't know how to read a schematic but it looks like a schematics "dictionary" is readily available online and I will look for the symbol "fuse" and check for internal ones.
I assume if the repair is as difficult as you suggest it may be, it should be handled by a pro or that I should (probably) look for a replacement. I have not found a Hafler P1500 (85 W/channel into 4 ohms) on ebay. Do you have a suggestion for a reasonable (low cost) replacement unit? I'm a bit more of a musician than an audiophile, but here and there the two meet.
My dad worked for Tektronix from about 1950 through 1985, starting out with oscilliscope design and eventually became a VP and ran their manufacturing operation in the "glory days". Many examples of the 500-series scopes were seen to glow on my dad's workbench in the basement over the years.
Bill
Power rails
Hi bpolits, it is rather strange that the amp got damaged - output FETs are "self-protecting" if there is no signal. Probably there was a signal, which was not a good idea 😉
Anyway, I would start with measuring the voltage at the power rails.
What are the voltages at L_B+ and L_B- points against the "Ground"?
As I can see from schematic, there is a line fuse, which is an "overall" fuse and this one seems to be ok, from what you noted earlier.
Two 1A fuses are protecting the low voltage / low power rails, used for powering the op-amps and VAS - those ones most likely would not have blown because of the output shortage... however, if some transistor is dead in the VAS circuit - could be. Anyway, check the +/- 18 volts as well, just to make sure.
By the way, the picture at the manual shows the LEDs, 4 per channel, indicating the protection circuit status - have you got them at your P1500? If yes - what do they show?
I put the link to service manual in my dropbox for everyone who tries to help here so that we all refer to the same source:
Hafler P1500 service manual
Output FETs are easily available on ebay:
2sk1058 / 2SJ162
Even available at the local store here in Moscow, the funny thing - price for 2sk1058 is $15 per piece, for 2SJ162 - $5
3 times difference 😀
Hope this helps,
Valery
Hi bpolits, it is rather strange that the amp got damaged - output FETs are "self-protecting" if there is no signal. Probably there was a signal, which was not a good idea 😉
Anyway, I would start with measuring the voltage at the power rails.
What are the voltages at L_B+ and L_B- points against the "Ground"?
As I can see from schematic, there is a line fuse, which is an "overall" fuse and this one seems to be ok, from what you noted earlier.
Two 1A fuses are protecting the low voltage / low power rails, used for powering the op-amps and VAS - those ones most likely would not have blown because of the output shortage... however, if some transistor is dead in the VAS circuit - could be. Anyway, check the +/- 18 volts as well, just to make sure.
By the way, the picture at the manual shows the LEDs, 4 per channel, indicating the protection circuit status - have you got them at your P1500? If yes - what do they show?
I put the link to service manual in my dropbox for everyone who tries to help here so that we all refer to the same source:
Hafler P1500 service manual
Output FETs are easily available on ebay:
2sk1058 / 2SJ162
Even available at the local store here in Moscow, the funny thing - price for 2sk1058 is $15 per piece, for 2SJ162 - $5
3 times difference 😀
Hope this helps,
Valery
Valery and everyone,
You are quite kind to offer a path forward and resources. Unfortunately, I can't answer the question about L_B+, ground, etc because though I can find these on the schematic, I do not know what they correspond to on the amp. I have tried to find some basic resources on the web that would help me answer these basic questions, but haven't had any luck yet.
The only question I can at this point answer is with regard to the LEDs:
When I power on the unit, channel 1 & 2 green "signal" LEDs shine; soon after, however, channel 1's LED goes out while channel 2's LED stays on.
Also, channel 1's output is extremely limited while channel 2 is dead. Also, channel 2's heat sink gets quite warm in just a couple of minutes with the power switch turned on.
You are quite kind to offer a path forward and resources. Unfortunately, I can't answer the question about L_B+, ground, etc because though I can find these on the schematic, I do not know what they correspond to on the amp. I have tried to find some basic resources on the web that would help me answer these basic questions, but haven't had any luck yet.
The only question I can at this point answer is with regard to the LEDs:
When I power on the unit, channel 1 & 2 green "signal" LEDs shine; soon after, however, channel 1's LED goes out while channel 2's LED stays on.
Also, channel 1's output is extremely limited while channel 2 is dead. Also, channel 2's heat sink gets quite warm in just a couple of minutes with the power switch turned on.
bpolits, try this site it shows how to check and see whats going on in a amplifier to aid repair...basic car amplifier repair..
plus when replacement mosfets have been fitted there need rebiasing as not to over heat and burn out..
plus when replacement mosfets have been fitted there need rebiasing as not to over heat and burn out..
Last edited:
Before Mr. Vzaichenko, so much negativity. I fixed my first transistor amp with a VOM and no schematic diagram. The transistor were so burned I couldn't tell PNP from NPN. But I got it working by checking transistors and diodes they read 0.6 v forward, 1999 backwards, resistors what they said on the label, and capacitors 1999.Also check that the resistance from one part to the next is zero, I've had some burned off PCB leads (I repaired with wire). The Hafler is old and probably has leaded parts which are removable with $70 in tools. Your ahead! A perfect project to learn on.
Before diving in check the voltage on the big capacitors to see if they are rated over 25 VDC. (Probably 85 v with a name like "1500"). Voltage over 25 is enough to be dangerous, so read the safety sticky on the tube amp forum about working around high voltage. No jewelry, use one hand at a time with the power on (clip lead on meter negative), discharge capacitors to 25 v or 0 (better) before mucking around with both hands. I've been hit by 400 VDC before safety stick threads were invented; if you use one hand only, it just hurts a little, it doesn't stop your heart like a two handed mistake can do.
From what you did I will wager that if you didn't blow a fuse, you blew some output transistors. When those blow, the rail voltage leaks out and blows up other stuff. I had to put 107 parts in my PV1.3k, but it was more fun than crossword puzzles that I don't know the sports and celebrity answers to.
You'er ahead, MR VZ has told you what the output transistors are. They are for sale, genuine ones Mr. Finch told me, in California, for $45 for 3 pairs last time I looked. Also there is a sub at newark.com from a different manufacture (not toshiba) under a different number. Search for that thread, substitutes for those part numbers.
I would remove some output transistors and test them. The part datasheets are on datasheetcatalog.com. You short the gate to the drain and see if current will flow from source to drain. If it will, the transistor is blown. The polarity matters, nfets hold off plus on the source, pfets hold off minus. Check the datasheet if I am wrong this is the wrong computer for me to do it now. I found on junction transistors, some were partially blown, they would pass a diode test on a meter at 2 v. But when I put rail voltage on them, they would blow up after a minute (wear safety glasses). When I put 17 VDC on them with a meter milliamp circuit in series, the ones that would blow up, werer leaky (non-zero current). I just used clip leads and a 12 v car batter charger with a capacitor on it to hold the peak voltage. I also put a 47 k resistor in series with the battery charger and meter to avoid blowing up the meter fuse if the transistor was zorked or I had the polarity backwards (current through the body diode).
Then check the emitter resistors, then work backwards from the gate to see what else is blown up. Some capacitors shorted, some just acted weird, and I don't have a capacitor meter, so I just replaced some capacitors with junk ones salvaged from PCAT power supplies or printer boards or other old junk. I didn't buy many parts but for the output transistors. Don't forget new heat sink compound on your newark/mouser/digikey order, and wash that stuff off after touching, it is poisonous. Don't buy parts on E-bay, many are counterfeit.
If you get to an AC problem like a bad solder joint keeping the music from flowing, you'll need a VOM with a 2 VAC scale and 20 VAC scale, or a VTVM, or a sound probe, or a scope. DVM don't read music worth a ****, only power line frequencies. I put music in with a transistor radio (isolated from ground by the battery) and trace the beats of rock and roll music through the circuit (the meter pointer jumps) until it stops.
Have fun.
Before diving in check the voltage on the big capacitors to see if they are rated over 25 VDC. (Probably 85 v with a name like "1500"). Voltage over 25 is enough to be dangerous, so read the safety sticky on the tube amp forum about working around high voltage. No jewelry, use one hand at a time with the power on (clip lead on meter negative), discharge capacitors to 25 v or 0 (better) before mucking around with both hands. I've been hit by 400 VDC before safety stick threads were invented; if you use one hand only, it just hurts a little, it doesn't stop your heart like a two handed mistake can do.
From what you did I will wager that if you didn't blow a fuse, you blew some output transistors. When those blow, the rail voltage leaks out and blows up other stuff. I had to put 107 parts in my PV1.3k, but it was more fun than crossword puzzles that I don't know the sports and celebrity answers to.
You'er ahead, MR VZ has told you what the output transistors are. They are for sale, genuine ones Mr. Finch told me, in California, for $45 for 3 pairs last time I looked. Also there is a sub at newark.com from a different manufacture (not toshiba) under a different number. Search for that thread, substitutes for those part numbers.
I would remove some output transistors and test them. The part datasheets are on datasheetcatalog.com. You short the gate to the drain and see if current will flow from source to drain. If it will, the transistor is blown. The polarity matters, nfets hold off plus on the source, pfets hold off minus. Check the datasheet if I am wrong this is the wrong computer for me to do it now. I found on junction transistors, some were partially blown, they would pass a diode test on a meter at 2 v. But when I put rail voltage on them, they would blow up after a minute (wear safety glasses). When I put 17 VDC on them with a meter milliamp circuit in series, the ones that would blow up, werer leaky (non-zero current). I just used clip leads and a 12 v car batter charger with a capacitor on it to hold the peak voltage. I also put a 47 k resistor in series with the battery charger and meter to avoid blowing up the meter fuse if the transistor was zorked or I had the polarity backwards (current through the body diode).
Then check the emitter resistors, then work backwards from the gate to see what else is blown up. Some capacitors shorted, some just acted weird, and I don't have a capacitor meter, so I just replaced some capacitors with junk ones salvaged from PCAT power supplies or printer boards or other old junk. I didn't buy many parts but for the output transistors. Don't forget new heat sink compound on your newark/mouser/digikey order, and wash that stuff off after touching, it is poisonous. Don't buy parts on E-bay, many are counterfeit.
If you get to an AC problem like a bad solder joint keeping the music from flowing, you'll need a VOM with a 2 VAC scale and 20 VAC scale, or a VTVM, or a sound probe, or a scope. DVM don't read music worth a ****, only power line frequencies. I put music in with a transistor radio (isolated from ground by the battery) and trace the beats of rock and roll music through the circuit (the meter pointer jumps) until it stops.
Have fun.
Last edited:
Turned the other computer on and I've got drain and source backwards, I always do that on FETs. Source is the one your short the gate to, to test them. On alf08n16v the gate is on the left the source is the one in the middle looking from the labeled side (non heat sink side). These are the subs I think, from alfet. the PMOS one is alf08p16v. 20 v just means more volts standoff, should substitute. These are lateral fets for linear amps; they act rather differently then switching fets that are 99.9% of the ones available.
Last edited:
- Status
- Not open for further replies.