Hey everyone! i just got this amplifier, and even after i did some rudimentary checks with my ohm meter (speaker terminals not shorted, fuses all good, measure collector to ground on the outputs, when powered on the transformer let out a loud hum as is there was a dead short somewhere. No smoke or anything else bad. The fan doesnt even start.
there is a capacitor C124 on one of the drive boards that is burnt, R128 has a massive burn mark up the side of it (but measures fine in circuit), but strangely (someone has at least tried to fix it before i got to it i believe) R127, and R123 have been replaced and measure fine. In circuit, CR110 and CR107 are dead shorted.
None of the outputs measure shorted in circuit.
I am going to check the crowbar circuits on the outputs shortly. However, here is another problem, there is a small board (about 2.5x2.5 in.) where the power switch and circuit breaker on the front of the unit connect to, among other things. I cannot find this board or its associated components mentioned in the schematic anywhere. There is a small 1/4 watt resistor that has broken in half, with the bands being red, red, (cant tell third) gold.
Someone has also soldered a low value resistor in series with one half of the power switch which then runs to what i believe is a large triac mounted directly to the bottom of the chassis.
Does anyone have any tips/common failures they can share? helpful measurements I could make? or be able to provide a schematic for the small board so i can replace the resistor and sort out the mess the last tech made with the soft start circuit? thank you so much, Dan.
Peavey 1.3k dead
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j0nsnell
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Re: Peavey 1.3k dead
R128 is a 4k 5W wire wound and does run hot.
C124 is a 0.033uF capacitor sat across the bias voltage.
I would suggest if that has burnt, a large voltage was present across it and that means the power amp has probably failed catastrophicaly.
Service information link; https://elektrotanya.com/peavey_1.3k_ma ... nload.html
C124 is a 0.033uF capacitor sat across the bias voltage.
I would suggest if that has burnt, a large voltage was present across it and that means the power amp has probably failed catastrophicaly.
Service information link; https://elektrotanya.com/peavey_1.3k_ma ... nload.html
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Douglasfir97
- New Member
- Posts: 2
- Joined: Sat Dec 07, 2024 6:24 pm
Re: Peavey 1.3k dead
more detail...
Hey everyone, I just got this peavey 1.3k amplifier. It has obviously been worked on my someone that didnt know what they were doing. Initial symptom was a loud hum from the power transformer when turned on. I cut the power fast, there was no smoke, the fan did not start at all.
So far I have found the following,
Driver board. (only one affected, other seems fine)
1. C223 replaced with a 15k resistor, according to manual should be .015 50v multilayer ceramic capacitor
2. C225 0.33uf multilayer ceramic capacitor (burned) Cannot find correct value so I am going to substitute with 0.33uf at 63V film type.
3. R217 100 ohm 1/4w was replaced, but had previously burned (large carbon marks).
4. CR210 1n4148 diode, shorted, replaced.
5. R227 manual says should be 4.7k 1/4 W but 15k 1/4W was installed. Working driver board has a 1.5k 1/4 W installed. (can tell this was indeed from the factory this way). I am guessing that since the working board has a 1.5k 1/4 W installed, that it is the correct value, but the schematic says otherwise...
Output stages.
1. One channel has original peavey transistors, emitters, etc. Installed. Quick in circuit testing reveals this channel to be ok.
2. Second channel has been replaced with MJ15024/25 transistors, fine. Q112 was oddly substituted for a “YS6900” motorola transistor, which reads open collector to emitter, out of circuit, both directions. None of the other transistors (mj15024/25s) measure bad. All emitter resistors read fine, except for two missing emitter resistors off of Q114 and Q119. Will replace with correct 0.33 ohm 5W
3. all of the 2.2k 1/4 W resistors next to the emitter resistors (which are original on the working channel) are actually 1.3k 1/4 W. Again, this is from the factory on the good channel. Some of these have burned out violently on the bad channel but have actually been replaced prior to me getting the unit.
4. I have removed and checked both channels crowbar triacs and they both test good. The one on the bad channel was replaced CR144, CR244.
Measuring from collector to ground on both channels reads around 16 Mohms. (bad channel missing the two emitter resistors and one output transistor that was substituted. I am not able to find a replacement of the original SAC187, digikey won't sell less than 300 of them, can anyone point me to a reputable seller that has originals?
Small 2.5x2.5” AC power board...
this board is part of the soft start circuit.
1. R1, 22 ohm 1/4W was completely blown in half. Have not replaced yet. Otherwise board tests fine.
2. main power switch has 120V AC hot on two terminals in/out, and two more terminals that i believe are for the soft start circuit. The other two terminals are a black wire and a yellow wire, previous tech has cut the black wire, and soldered a 200 ohm 1/2 W resistor in series with it. It now goes directly to one terminal of what I believe is the soft start triac, mounted on the bottom of the chassis. I cannot find this triac on any of the schematics I have.
J4 on the small 2.5x2.5” board has nothing connected to it, i believe it is for part of the soft start circuit the previous tech has modified. I would like to return everything to factory wiring. Can anyone help me here?
I will not be powering the unit up again without significant current limiting, and being 100% sure there are no shorts or opens anywhere. I am being extremely careful not to do more damage.
If anyone can please offer assistance, advice, experience, I would greatly appreciate it. Sorry for this being so long but details are critical here.
Hey everyone, I just got this peavey 1.3k amplifier. It has obviously been worked on my someone that didnt know what they were doing. Initial symptom was a loud hum from the power transformer when turned on. I cut the power fast, there was no smoke, the fan did not start at all.
So far I have found the following,
Driver board. (only one affected, other seems fine)
1. C223 replaced with a 15k resistor, according to manual should be .015 50v multilayer ceramic capacitor
2. C225 0.33uf multilayer ceramic capacitor (burned) Cannot find correct value so I am going to substitute with 0.33uf at 63V film type.
3. R217 100 ohm 1/4w was replaced, but had previously burned (large carbon marks).
4. CR210 1n4148 diode, shorted, replaced.
5. R227 manual says should be 4.7k 1/4 W but 15k 1/4W was installed. Working driver board has a 1.5k 1/4 W installed. (can tell this was indeed from the factory this way). I am guessing that since the working board has a 1.5k 1/4 W installed, that it is the correct value, but the schematic says otherwise...
Output stages.
1. One channel has original peavey transistors, emitters, etc. Installed. Quick in circuit testing reveals this channel to be ok.
2. Second channel has been replaced with MJ15024/25 transistors, fine. Q112 was oddly substituted for a “YS6900” motorola transistor, which reads open collector to emitter, out of circuit, both directions. None of the other transistors (mj15024/25s) measure bad. All emitter resistors read fine, except for two missing emitter resistors off of Q114 and Q119. Will replace with correct 0.33 ohm 5W
3. all of the 2.2k 1/4 W resistors next to the emitter resistors (which are original on the working channel) are actually 1.3k 1/4 W. Again, this is from the factory on the good channel. Some of these have burned out violently on the bad channel but have actually been replaced prior to me getting the unit.
4. I have removed and checked both channels crowbar triacs and they both test good. The one on the bad channel was replaced CR144, CR244.
Measuring from collector to ground on both channels reads around 16 Mohms. (bad channel missing the two emitter resistors and one output transistor that was substituted. I am not able to find a replacement of the original SAC187, digikey won't sell less than 300 of them, can anyone point me to a reputable seller that has originals?
Small 2.5x2.5” AC power board...
this board is part of the soft start circuit.
1. R1, 22 ohm 1/4W was completely blown in half. Have not replaced yet. Otherwise board tests fine.
2. main power switch has 120V AC hot on two terminals in/out, and two more terminals that i believe are for the soft start circuit. The other two terminals are a black wire and a yellow wire, previous tech has cut the black wire, and soldered a 200 ohm 1/2 W resistor in series with it. It now goes directly to one terminal of what I believe is the soft start triac, mounted on the bottom of the chassis. I cannot find this triac on any of the schematics I have.
J4 on the small 2.5x2.5” board has nothing connected to it, i believe it is for part of the soft start circuit the previous tech has modified. I would like to return everything to factory wiring. Can anyone help me here?
I will not be powering the unit up again without significant current limiting, and being 100% sure there are no shorts or opens anywhere. I am being extremely careful not to do more damage.
If anyone can please offer assistance, advice, experience, I would greatly appreciate it. Sorry for this being so long but details are critical here.