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Messages - vintagekiki

Pages: [1]
1
Schematics and Layouts / Re: Yamaha JX20 Service Manual
« on: May 31, 2019, 03:37:15 AM »
https://www.owner-manuals.com/-manuals-1-20a.html?alpha_filter_id=74

See YAMAHA JX20 Owner's Manual page 7 (block diagram)  for the difference between amps JX20 and other JX series amps.

2
Amplifier Discussion / Re: Out of rehab into recovery
« on: October 24, 2018, 03:54:58 PM »
My question is how hot does the back panel get when playing at volume, I know this is a bit subjective with out a proper reading, but it was quite warm after being played hard on stage setting for 10 mins or so. I pulled it from the cabinet and the two TIP drivers where more than warm but not burning to the touch (not uncomfortable and no smell)
would this be acceptable ?

The best test of whether the amplifier overheats or not, is to follow the rear panel (heat sink) heating for 30 minutes without the signal (guitar is not connected).

The operating temperature of the rear panel (heat sink) without the signal should be slightly warm up to 30-40 degrees.
When the signal (guitar) is connected to the amplifier  and when playing a loud, normal operating temperature the rear panel (heat sink) is very hot to 70-80 degrees.

Tip
When examining passive components, be careful not to make a mistake in interpreting the measured nominal value and tolerance ratings.
The usual tolerance rating of most components is +/- 10-20% except aluminum electrolytic's which can range from -20% to as high as + 80%


https://www.google.com/search?q=resistor+and+capacitor+tolerance+rating

3
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 22, 2018, 11:57:25 AM »
The collector current that flows through TIP29/30C creates a voltage drop on resistors R29 / R33 = 33 Ohm connected between the base and the emitter of the output transistors 2N3773, and in this way provides the necessary bias for their operation.

Transistors for their work should have a voltage between the base and the emitter about 0.55 - 0.7V.

At low power transistors on PCB, ebc connections are near, so you need to be careful when performing measurements directly on transistors

Tip
For future reference when the power amp repair, replace the defective output transistor(s), the emitter resistor(s) of the defective output transistor(s), the both resistors of the base/emitter of the output transistors, the drivers if the defects are changed in pairs (TIP29/30C), check and adjust the idle current (25-30 mA per pair of output transistors).
Check the DC offset (≤ 100mV) of the speaker jack connector and that's it.

4
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 16, 2018, 03:09:00 AM »
I'm not old-fashioned, but the ohmmeter in the analog multimeter 20 kohm/V (with pointers) best proved for a semiconductor test in the circuit.
Measurement with ohmmeter (measurement range x10 or x100) can detect a faulty semiconductor in a circuit without desoldering.
If you have a 2 amplifier with the same part number PCB (for example AS 00014/2), simply compare the same semiconductor in the same conditions in the correct and in the faulty amplifier.

Warning.
Disconnect amplifier from the AC outlet.

When any measuring with ohmmetar, amplifier must be disconnect from the AC outlet.
When desolder any component, the amplifier must be disconnect from the AC outlet.

5
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 14, 2018, 06:26:19 PM »
Do not replace ad hoc any transistors, if not previously tested them in what condition.
Test each transistor with the multimeter in the circuit or removed from the circuit.

Testing a transistor with an analogue multimeter

https://www.radio-electronics.com/info/t_and_m/analogue-multimeter-voa-vom/testing-diode-transistor-with-multimeter.php
https://www.instructables.com/id/How-to-test-Bipolar-Transistors-if-you-have-an-Ana/
https://www.scribd.com/doc/34162981/Transistor-Test-Using-an-Analogue-Multi-Meter
https://www.mikroe.com/ebooks/components-of-electronic-devices/diodes-and-transistors
http://120studio.com/tech/transistors.htm


Simple transistor testers
https://www.elprocus.com/simple-transistor-tester-circuit/
http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/images/TransistorTester.gif
https://electronicsforu.com/electronics-projects/hardware-diy/easy-transistor-tester


From the 30 year practice, the most common failures in power amp are the output transistors 2N3773, the driver transistors TIP29C/30C, the emitters resistance 0.33Ω/6W.
After each power amp repair, necessarily set the idle current 2N3773, and check the DC offset on speaker output jacks.

Reminder for advanced users
If you have tone generator, oscilloscope, audio voltmeter and 8 Ω dummy load, by measuring voltage at audio voltmeter, check at the oscilloscope at which power, power amp is symmetrically limited.
P = U2 / R

6
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 13, 2018, 05:07:41 AM »
p.s. amplifier is still working but sound remains distorted at any volume
Turn guitar to poweramp input jack (rear amp).
In this way, you separate the preamplifier from the power amp.
The sound from the amplifier will be much smaller.

- If the sound is further distorted, fault is in the power amp.
- If the sound is clean (non-distorted) fault is in the preamplifier.

7
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 11, 2018, 10:50:57 PM »
... there is 4mv on the speaker out jacks ...

The DC offset voltage is OK (allowed max 50-100mV)

... measuring over the 4A resistors i get around 4.5mv ...

idle current power amp with high accuracy can be measured by measuring the idle current 2N3773 described at
https://www.ssguitar.com/index.php?topic=4500.msg36012#msg36012

a. recommended value measurement with DC milliampmeter 25-40mA
or
b. recommended value measurement with DC millivoltmeter 25-40mV

8
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 10, 2018, 10:02:07 PM »
For comparison I checked my HH VS musician amps readings and get around 11mv on it's OR33's

11mv on it's OR33's on your HH VS musician amps is 33 mA idle current and that's OK.
When replacing the transistor, check that the CBE transistor layout is the same.

Question.
Is there and how much is DC offset on speaker output jacks?

How much is the current, and how much is the DC voltage without signal at + and - supply rail (measured at Fuse 4A)

9
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 09, 2018, 05:24:07 PM »
DC mv across  R28    = 5.1mv
DC mv across  R34    = 4.9mv

In your case if R28 = R34 = 0.33 Ω idle current through 2N3773 is
DC mv across  R28    = 5.1mv = 0.0155 mA
DC mv across  R34    = 4.9mv = 0.0148 mA
2N3773 are at beginning opening
For optimal bias idle current it should be increased to 25-40mA

10
Amplifier Discussion / Mounting a transistor to heatsink
« on: October 09, 2018, 09:00:13 AM »
- When replacing the output transistors, it is  necessary to clean the heatsink and insulating washer from the old thermally conductive paste with a some solvent on a nitro base.
- In order to better cool the transistors, apply to the insulating washer fresh thermally conductive paste on both sides.


https://rimstar.org/equip/mount_transistor_heatsink.htm
Mounting a transistor to heatsink

https://www.youtube.com/watch?v=hNRacVQRgBc
How to mount/attach transistor to heatsink

11
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 07, 2018, 04:26:23 PM »
Reminder

- If you use an oscilloscope during service, be aware that the speaker is not directly connected to the ground, already is connected via the resistor R32 (0R1).

- The DC offset voltage allowed on the speaker jack is max 50-100mV

- When the power amp is defective, a DC voltage of up to 40V can occur on the speaker jack.
During repairs to protect from further damage connect speaker jack with speaker or dummy load via capacitor 2200 - 4700 uF/ 63V

- A simple current limiter to safe amp repairs can be done if instead fuse 4A in +/- 47V supply puts the resistors 100 ohm/50W

- Easy setup of the correct bias by adjusting the idle current.
a. Measurement the idle current when instead fuse 4A at point + 47V connect the DC milliampmeter (range 200mA). The idle current adjusts to value of 25-40mA by changing the resistor R15 (AOT)
b. Measurement the idle current when instead fuse 4A at point + 47V connect resistor 1R/2W and parallel with resistor connect DC millivoltmeter (range 200mV). The idle current adjusts to value of 25-40mV by changing the resistor R15 (AOT)

12
Amplifier Discussion / Re: HH IC100 overheating BD711 transistor...help !
« on: October 06, 2018, 05:31:41 PM »
HH amplifiers series 100 as driver transistors use TIP29/30C.
Overheating the transistor driver can occurs if the replaced driver transistor has a larger hfe than the original driver transistor.

Each replacement driver or output transistor implies the setting of a quiet current (output) transistor.
Adjusting the quiet current is done with a fine change of the resistor R15 (AOT) which is connected in parallel with the resistor R14 (100 Ohm)
The large quiet current of the output transistors makes a great quiet current of the TIP29/30C transistor, which can be one of the reasons for heating TIP29/30C.
Driver transistor TIP29/30C and output transistor 2N3773  should be mutually matched within 10%.


TIP29/30C Datasheet
http://html.alldatasheet.com/html-pdf/2777/MOSPEC/TIP29C/145/1/TIP29C.html
http://html.alldatasheet.com/html-pdf/2781/MOSPEC/TIP30C/145/1/TIP30C.html

TIP29/30C Replacement
https://www.el-component.com/bipolar-transistors/TIP29C
https://www.el-component.com/bipolar-transistors/TIP30C

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