Punch 500a2 distorted channel

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Do you have any solder bridges between the pads for the outputs?

Confirm with your meter set to ohms that no two adjacent pads read near 0 ohms. Check all of the output pads for this channel.

Can I ask where am I getting 24 volts from on the driver transistor? Explains why things were getting hot. I really want to fix this but I am unsure where the source is on this problem. What would be an approximate 'good' reading for the SMT parts when measuring continuity?

I am starting to hate this amplifier.....! -.-
 
Did you check for the bridges between the pads with your meter?

Things are unpredictable (voltage-wise) when components are missing from the feedback loop (this includes the outputs). If you want to repair this, you need to eliminate one problem at a time.

If you're checking components in the circuit, you can compare one channel to the other (meter on resistance, probe placement identical for each component being checked, no power applied to the amp).
 
Did you check for the bridges between the pads with your meter?

Things are unpredictable (voltage-wise) when components are missing from the feedback loop (this includes the outputs). If you want to repair this, you need to eliminate one problem at a time.

If you're checking components in the circuit, you can compare one channel to the other (meter on resistance, probe placement identical for each component being checked, no power applied to the amp).


I did and I didn't get anything near 0 from gate, drain, source i did get high resistance readings thought from source to drain, drain to source. I also replaced a 2A transistor with another working 2A transistor.

What if the bias pot is turned up?? Could this cause problems?
 
It should be set fully counter-clockwise until you get the outputs reinstalled and clamped down.

I'd suggest that you install the outputs, clamp them down tightly to the heatsink, insert a 10 amp ATC/ATO fuse in the B+ line and power the amp up.

Does the fuse blow?

Do you have any significant DC across the speaker terminals of the repaired channel?
 
It should be set fully counter-clockwise until you get the outputs reinstalled and clamped down.

I'd suggest that you install the outputs, clamp them down tightly to the heatsink, insert a 10 amp ATC/ATO fuse in the B+ line and power the amp up.

Does the fuse blow?

Do you have any significant DC across the speaker terminals of the repaired channel?

I have new outputs, but i don't want to blow them and the old ones are shorted but I'll give it a try even if it shorts the new ones. And yea I have a 5 amp fuse inserted at all times during testing, trouble shooting. But if it blows the new outputs what does this mean???
 
I use acetone. You can use 91% isopropyl alcohol but it's not as effective, sometimes leaves a white film and doesn't dry as quickly. It is, however, safer and more readily available.

The flux isn't generally conductive but if it gets heated too much or picks up a lot of contaminants, it can become slightly conductive. It's best to clean it off because it allows you to better see the solder connections and any tiny solder bridges.
 
I use acetone. You can use 91% isopropyl alcohol but it's not as effective, sometimes leaves a white film and doesn't dry as quickly. It is, however, safer and more readily available.

The flux isn't generally conductive but if it gets heated too much or picks up a lot of contaminants, it can become slightly conductive. It's best to clean it off because it allows you to better see the solder connections and any tiny solder bridges.

D104 & Q116 went poof when i reinstalled the driver transistor (MPSA56). I'm starting to give up on it. How much power can i expect out of one channel? 300 watts? or less? I haven't used the new IRF540s & IRF9540s becuase two parts blew up. Also how do you tin new FETs to install to the mehsa? I still need to put the IRF3205s in still.
 
I just turn the fets over and apply a small film of flux then heat them up with your iron till the flux starts to bubble then hold the solder to the fet until it melts, remove the iron briefly hold the legs with another tool or something then run your iron over the back of the fet and spread the solder. Be careful not to get them to hot and dont get excessive solder on them. It does not take much because keep in mind there is solder on the mesha pad as well. A butane torch works the best for heating the mesha board and installing the fets. The off color dull grey IRF 3205's tin much easier than the shiny chrome looking ones, the solder almost spreads itself on the dull colored ones. Hope this helps.
 
I just turn the fets over and apply a small film of flux then heat them up with your iron till the flux starts to bubble then hold the solder to the fet until it melts, remove the iron briefly hold the legs with another tool or something then run your iron over the back of the fet and spread the solder. Be careful not to get them to hot and dont get excessive solder on them. It does not take much because keep in mind there is solder on the mesha pad as well. A butane torch works the best for heating the mesha board and installing the fets. The off color dull grey IRF 3205's tin much easier than the shiny chrome looking ones, the solder almost spreads itself on the dull colored ones. Hope this helps.

I've already fix this problem... Sort of i got the power supply working great again. I just got the new fets and sanded them alittle on the back and applied flux and as i heated the mehsa i out solder on the solder pad and it worked out good.

Now has anyone fixed a punch 200a4? I bought one today one ebay for $23 as is. The seller claims it just stopped working out of now where. He sent me pictures of the inside and nothing looks blown. What cause this?? Shorted power supply?
 
I have repaired several punch 200a4 and 400a4 amps and a few 600a4 amps. " just stopped working " That is a vague description. If its a power supply problem due to a shorted output transistor it is an easy fix. First the power supply needs to be gone through. Replace all the power supply fets and their gate drivers. Then right by the TL494C pwm chip there are four smd transistors 2 of them are marked 1A and 2 of them are marked 2A, replace those four. DO NOT power up the amp. Test the output transistors they will be IRF540 and IRF9540. Find the bad ones and clip the leads from the board. Once you clip the leads of the bad output transistors the amp SHOULD power up just fine. As old as the amp is you should replace them all in all four channels. Replace their gate drivers as well. Test and replace the emitter resistors if needed. I use 0.1 ohm 2 watt and have NEVER had any issues. Always check the RCA ground pins to the board as well alot of times on Rockford amps they are broken. If they are replace both IN4003 zener diodes as well or you will get feedback and or noise through the outputs. I also take a look at the MPS 6521's and the MPS A56 and the MPS A06. I have had amps with distortion and these were bad. If you still have a distortion problem start looking to the smd components in the channels such as 5D and A7. The 1A and 2A transistors in the channels as well, the amp may still power up with these bad but can send dc to the output terminals. MOST IMPORTANT ALWAYS TURN THE BIAS POTS ALL THE WAY DOWN "COUNTER CLOCKWISE" BEFORE POWERING THE AMP AFTER REPAIRS AND USE A 5-10 AMP FUSE INLINE WITH THE B+ TERMINAL. Once you get the amp hit me up if you need help and or parts I stock thousands of parts for old school Rockford amps. I can also help you in resetting the bias once repairs are complete. Any questions dont hesitate to ask. Hope this helps.....
 
I have repaired several punch 200a4 and 400a4 amps and a few 600a4 amps. " just stopped working " That is a vague description. If its a power supply problem due to a shorted output transistor it is an easy fix. First the power supply needs to be gone through. Replace all the power supply fets and their gate drivers. Then right by the TL494C pwm chip there are four smd transistors 2 of them are marked 1A and 2 of them are marked 2A, replace those four. DO NOT power up the amp. Test the output transistors they will be IRF540 and IRF9540. Find the bad ones and clip the leads from the board. Once you clip the leads of the bad output transistors the amp SHOULD power up just fine. As old as the amp is you should replace them all in all four channels. Replace their gate drivers as well. Test and replace the emitter resistors if needed. I use 0.1 ohm 2 watt and have NEVER had any issues. Always check the RCA ground pins to the board as well alot of times on Rockford amps they are broken. If they are replace both IN4003 zener diodes as well or you will get feedback and or noise through the outputs. I also take a look at the MPS 6521's and the MPS A56 and the MPS A06. I have had amps with distortion and these were bad. If you still have a distortion problem start looking to the smd components in the channels such as 5D and A7. The 1A and 2A transistors in the channels as well, the amp may still power up with these bad but can send dc to the output terminals. MOST IMPORTANT ALWAYS TURN THE BIAS POTS ALL THE WAY DOWN "COUNTER CLOCKWISE" BEFORE POWERING THE AMP AFTER REPAIRS AND USE A 5-10 AMP FUSE INLINE WITH THE B+ TERMINAL. Once you get the amp hit me up if you need help and or parts I stock thousands of parts for old school Rockford amps. I can also help you in resetting the bias once repairs are complete. Any questions dont hesitate to ask. Hope this helps.....

Hey do you know about the old school The Punch 150? It's the very first punch 150 with the wires attached to the board. Anyway i have one here under my desk that has been sitting here for a very long time. I got for free but it is missing parts with some shorted parts. Can i use IRFZ44 for the SMPS? And do i have to change the gate resistors?
 
Is the one you have?
 

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