Is it possible to test the output trans while in circuit.?
I am asking about Q3-Q6 and Q13-Q16.
I have one of these..... https://www.amazon.com/Peak-Electronic-Design-Ltd-dca55/dp/B005NIR8G8
.....but will i need to lift these trans off the chassis to get a reliable test.?
Thank You
SCHEMATIC
https://dl.dropboxusercontent.com/u/3131065/Amps/Peavey Mark III/PV 400BH.pdf
I am asking about Q3-Q6 and Q13-Q16.
I have one of these..... https://www.amazon.com/Peak-Electronic-Design-Ltd-dca55/dp/B005NIR8G8
.....but will i need to lift these trans off the chassis to get a reliable test.?
Thank You
SCHEMATIC
https://dl.dropboxusercontent.com/u/3131065/Amps/Peavey Mark III/PV 400BH.pdf
not with that machine.
Most "tests" require a specific test setup to measure the parameter you are interested in. One generally can't do that "in circuit".
Fatal faults can show up with just a multimeter.
i.e. short form c to e.
You can check other junctions with multimeter but other components can affect the readings.
i.e. short form c to e.
You can check other junctions with multimeter but other components can affect the readings.
Gotcha...i will have to unscrew and desolder these guys.
Right now Q14-15-16 are reading a short from E to B. Q13 gives a non reading with a Peak/Atlas trans tester.
Anyway.....time to pull these.
Thanks
Right now Q14-15-16 are reading a short from E to B. Q13 gives a non reading with a Peak/Atlas trans tester.
Anyway.....time to pull these.
Thanks
All the collectors and bases are tied together, so if one of your transistors is shorted, your continuity tester will not find which one...
If continuity testing shows nothing wrong though, they could all be OK.
If continuity testing shows nothing wrong though, they could all be OK.
OK...Great...Thank You.
I can look at a tube amp schem and follow the current through most of it,
With SS amp..... i am JUST learning how a NPN or PNP is biased, so at this point a SS schem just looks like a mess to me, if you know what i mean.
Thanks Again For The Help
I can look at a tube amp schem and follow the current through most of it,
With SS amp..... i am JUST learning how a NPN or PNP is biased, so at this point a SS schem just looks like a mess to me, if you know what i mean.
Thanks Again For The Help
npn - How do I check a BJT transistor if it is still functional? - Electrical Engineering Stack Exchange
What symptoms is your amp exhibiting?
0V at output?
Rail voltage on output?
Both channels dead or just one?
Distorted sound?
Do you own a scope?
What makes you suspect the output transistors might be blown?
What symptoms is your amp exhibiting?
0V at output?
Rail voltage on output?
Both channels dead or just one?
Distorted sound?
Do you own a scope?
What makes you suspect the output transistors might be blown?
Yeah.....sorry.
Loud Hum/Buzz on both channels.
A high school kid in my neighborhood brought this to me. He complained of no sound coming out the speaker and a very loud hum.
I had it powered up with a guitar in the front end and a 8 Ohm Speaker.... and i heard the same.
I disconnected the 15 Volt supply (with the amp On) and the hum went away. I reconnected the 15V, the buzz came back and then, 15-20 seconds later.....R58 smoked and the 8 Amp fuse snapped.
I shut down, replaced R58, lifted as much stuff as needed to isolate the rectifiers and 5500 Mic caps. The diodes all tested good.
The caps tested good with my ESR meter. Though they ARE 30-40 years old and Might be bad with power applied.?
But with R58 gone i thought the transistor(s) might have been damaged.
Somebody has been in this amp before. Q13 and some ocher parts have been replaced.
There is what looks like a burn mark under R25. It is a carbon comp and all the other resistors are carbon film or metal film.
Anyway.....all the rectifiers tested about 0.520 Volts. The two 5500uF caps were about 0.15 Ohms. I now have the amp on a current limiter and the 100 watt bulb is bright.
I have a short somewhere, and i have started to suspect the power transistors.
Thank You
My biggest problems:
1. I am completely unfamiliar with SS Amps.
2. I am not sure how to trouble-shoot with the amp on a limiter.
Loud Hum/Buzz on both channels.
A high school kid in my neighborhood brought this to me. He complained of no sound coming out the speaker and a very loud hum.
I had it powered up with a guitar in the front end and a 8 Ohm Speaker.... and i heard the same.
I disconnected the 15 Volt supply (with the amp On) and the hum went away. I reconnected the 15V, the buzz came back and then, 15-20 seconds later.....R58 smoked and the 8 Amp fuse snapped.
I shut down, replaced R58, lifted as much stuff as needed to isolate the rectifiers and 5500 Mic caps. The diodes all tested good.
The caps tested good with my ESR meter. Though they ARE 30-40 years old and Might be bad with power applied.?
But with R58 gone i thought the transistor(s) might have been damaged.
Somebody has been in this amp before. Q13 and some ocher parts have been replaced.
There is what looks like a burn mark under R25. It is a carbon comp and all the other resistors are carbon film or metal film.
Anyway.....all the rectifiers tested about 0.520 Volts. The two 5500uF caps were about 0.15 Ohms. I now have the amp on a current limiter and the 100 watt bulb is bright.
I have a short somewhere, and i have started to suspect the power transistors.
Thank You
My biggest problems:
1. I am completely unfamiliar with SS Amps.
2. I am not sure how to trouble-shoot with the amp on a limiter.
Check for huge DC offset on output. Some of the output transistors may be blown, and perhaps some others...
To be honest, i am not even sure how to check DC Offset. I thought that was a stereo thing...across two outputs.?
Anyway, how do i check that on this PV.....and i can do that while it is on a limiter?
Thank You
Anyway, how do i check that on this PV.....and i can do that while it is on a limiter?
Thank You
Also be aware that unlike most Valve amps, solid state amplifiers will have symmetric supplies - that is, a +ve and -ve voltage with respect to ground. Both of these supplies must be present to operate correctly.
On the schematic you have posted, you can see that there is +52V and -52V powering the output stage. You can also see that there are +15v/-15v supplies produced by regulation with Zener diodes (CR20, CR21) and another set of +16/-16v supplies, produced by VR1 and VR2.
If you can, isolate these power supply connections, and test that they are all present with respect to ground. The -ve speaker terminal will do as a ground point. You should see stable DC voltages with very little/no AC. It will be worth checking the rectifier diodes CR16-19. If any are short or open, replace all of them. Capacitors C35 and C36 will certainly be past their best life by now, but loud hum would indicate a more serious fault.
On the schematic you have posted, you can see that there is +52V and -52V powering the output stage. You can also see that there are +15v/-15v supplies produced by regulation with Zener diodes (CR20, CR21) and another set of +16/-16v supplies, produced by VR1 and VR2.
If you can, isolate these power supply connections, and test that they are all present with respect to ground. The -ve speaker terminal will do as a ground point. You should see stable DC voltages with very little/no AC. It will be worth checking the rectifier diodes CR16-19. If any are short or open, replace all of them. Capacitors C35 and C36 will certainly be past their best life by now, but loud hum would indicate a more serious fault.
To check DC offset, you get a DC meter and simply measure between the +ve and -ve speaker terminals. There should be no more than perhaps 100mV of DC. Over 1V is certainly sign of a serious fault.
Use your multimeter to measure DC voltage between one output terminal and GND. Check each channel independently.
If it reads -100mV... or 0V... or 100mV... then OK.
If it reads 10 or 30 volts, you got a problem. No speaker likes too much DC.
If it reads -100mV... or 0V... or 100mV... then OK.
If it reads 10 or 30 volts, you got a problem. No speaker likes too much DC.
R25 having a burn mark means that the output has at some point been shorted. The arrangement of Q1, Q7, CR10, CR14 and associated components form what is called a VI limiter. This basically monitors the current passing through R56/R57 and if it is too high, the transistors attempt to attenuate the drive signal to the output stage by limiting the drive voltage to Q2 and Q12. If this goes on for too long, components get damaged.
Resistors marked F.P. are fusible resistors - meaning they are designed to burn out like fuses if excessive current passes through them. Check ALL of these to see if any are open circuit.
Unfortunately the best way to check the output transistors is out of circuit. Often such transistors fail short from collector-emitter, or all 3 terminals short.
Generally the best approach for testing is to start at the output stage and work backward. Output transistors (Q4-Q6 and Q14-Q16) failing often take out the driver transistors (Q3, Q13) and associated components.. likewise failing drivers often take out predrivers (Q2, Q12). Excessive VI limitation often takes out the limiting transistors (Q1, Q7), their associated resistors/diodes, and often the predrivers.
Resistors marked F.P. are fusible resistors - meaning they are designed to burn out like fuses if excessive current passes through them. Check ALL of these to see if any are open circuit.
Unfortunately the best way to check the output transistors is out of circuit. Often such transistors fail short from collector-emitter, or all 3 terminals short.
Generally the best approach for testing is to start at the output stage and work backward. Output transistors (Q4-Q6 and Q14-Q16) failing often take out the driver transistors (Q3, Q13) and associated components.. likewise failing drivers often take out predrivers (Q2, Q12). Excessive VI limitation often takes out the limiting transistors (Q1, Q7), their associated resistors/diodes, and often the predrivers.
I also see now this is a Peavey amplifier. Peavey love to use their own transistor markings, so the part numbers on them will probably not read to anything you recognise.
For the output and driver transistors, I would go with these:
Q4-Q6: MJ15003, MJ15022, MJ15024
Q14-Q16: MJ15004, MJ15023, MJ15025
Q3: MJE15032
Q13: MJE15033
Aha, just found a crossreference list:
http://adrsoundsense.co.uk/technical/peavey/PV_Semi_Cross_Ref.pdf
For the output and driver transistors, I would go with these:
Q4-Q6: MJ15003, MJ15022, MJ15024
Q14-Q16: MJ15004, MJ15023, MJ15025
Q3: MJE15032
Q13: MJE15033
Aha, just found a crossreference list:
http://adrsoundsense.co.uk/technical/peavey/PV_Semi_Cross_Ref.pdf
OK.
I will check the off-set and report back. In the mean time, this kid is in a position of owning an amp that might need parts that exceed the value of buying another amp.
Of course there is no point in buying another "old amp", but people usually do not want to put 100 dollars of parts into a 50-100 dollar amp.
Yeah, the Elytics are all old at this point, and the 5500uF caps are rated at 55V with a schem voltage of 52V across them.
Again, i am new to SS, but I Think the next step up in cap voltage would be 63-70 Volts. Probably a good idea to boost that value.?
Anyway.....Thanks Again for all the help. I will let you know what this young man (or more likely his Father) wants to do. 🙂
Thank You So Much
I will check the off-set and report back. In the mean time, this kid is in a position of owning an amp that might need parts that exceed the value of buying another amp.
Of course there is no point in buying another "old amp", but people usually do not want to put 100 dollars of parts into a 50-100 dollar amp.
Yeah, the Elytics are all old at this point, and the 5500uF caps are rated at 55V with a schem voltage of 52V across them.
Again, i am new to SS, but I Think the next step up in cap voltage would be 63-70 Volts. Probably a good idea to boost that value.?
Anyway.....Thanks Again for all the help. I will let you know what this young man (or more likely his Father) wants to do. 🙂
Thank You So Much
Sorry if i am still confused about the off-set.
Am i supposed to measure between the +52 and -52.?
That number is about 15.5 Volts.
+52V to speaker jack tip is about 13.5V
and
-52V to speaker jack tip is about -2.2V
Is that the numbers you guys are looking for.?
Thank You
Am i supposed to measure between the +52 and -52.?
That number is about 15.5 Volts.
+52V to speaker jack tip is about 13.5V
and
-52V to speaker jack tip is about -2.2V
Is that the numbers you guys are looking for.?
Thank You
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