Hi there,
got a used and already repaired (power supply section) Zapco Studio 500.
Fired it up, signals are looking good so far, but DC offset is ~42mV on one channel, and ~25mV on the other. I think there is something wrong.
Before I change the transistors, fets and other stuff, I need to know how to adjust the power supply voltage and bias.
There are 3 pots, one for the voltage, and 2 pots for bias left and right. Question is, what values to set, and where to measure them? I know how to adjust these values on amps like Hifonics viii, but never did this on Zapcos.
Btw, the fan ist on all the time, dont know if this is normal for this amp. I thought it should only run and speed up when the amp is heating up!?
Idle current with fan on is about 1.8A, in the manual the idle current is about 2.2A with fan on!?
got a used and already repaired (power supply section) Zapco Studio 500.
Fired it up, signals are looking good so far, but DC offset is ~42mV on one channel, and ~25mV on the other. I think there is something wrong.
Before I change the transistors, fets and other stuff, I need to know how to adjust the power supply voltage and bias.
There are 3 pots, one for the voltage, and 2 pots for bias left and right. Question is, what values to set, and where to measure them? I know how to adjust these values on amps like Hifonics viii, but never did this on Zapcos.
Btw, the fan ist on all the time, dont know if this is normal for this amp. I thought it should only run and speed up when the amp is heating up!?
Idle current with fan on is about 1.8A, in the manual the idle current is about 2.2A with fan on!?
See attached pdf file for How to test the bias voltage while making adjustments. This is my preferred method. I attach my meter probes across the emitter resistors and monitor the bias voltage as I set it to factory spec's.
I also test across each individual resistor to make sure each transistors is acting the same in large paralleled arrays of outputs. Just something I picked up from one of the larger manufacturers long ago.
I don't know Zapco spec's for their bias, but anything from 0.0001 to 0.001 vdc < 100 micro-volts to 1 mvdc > will do in most cases. Some of the older Alpine and Kenwood gear use to spec as high as 2 to 4 mvdc.
The third pot your taking about could be used for many different things such as rail voltage set or power limit set for the amp, or even protection levels. I would need to see it's circuit usage to determine how and what it is used for and weather or not it should be adjusted at all....
1.8 amps current draw sounds about right. Fan running at low speed is also OK. If fan is running at high speed or not at all then the fan control circuit is likely damaged. Fan speed should be controlled by heat so look for a temp sensor and apply some heat to it to test the circuit to see if the fan speeds up. Typical temp sensor could be a TO-92 transistor, or a temp sense diode. Try applying some heat via a hot air wand or the tip of a soldering iron to the thermal sensors you see touching the heat sink and see what happens. If the fan speeds up I would say your good to go, and move on to other items on your list.... hope this helps some🙂
I also test across each individual resistor to make sure each transistors is acting the same in large paralleled arrays of outputs. Just something I picked up from one of the larger manufacturers long ago.
I don't know Zapco spec's for their bias, but anything from 0.0001 to 0.001 vdc < 100 micro-volts to 1 mvdc > will do in most cases. Some of the older Alpine and Kenwood gear use to spec as high as 2 to 4 mvdc.
The third pot your taking about could be used for many different things such as rail voltage set or power limit set for the amp, or even protection levels. I would need to see it's circuit usage to determine how and what it is used for and weather or not it should be adjusted at all....
1.8 amps current draw sounds about right. Fan running at low speed is also OK. If fan is running at high speed or not at all then the fan control circuit is likely damaged. Fan speed should be controlled by heat so look for a temp sensor and apply some heat to it to test the circuit to see if the fan speeds up. Typical temp sensor could be a TO-92 transistor, or a temp sense diode. Try applying some heat via a hot air wand or the tip of a soldering iron to the thermal sensors you see touching the heat sink and see what happens. If the fan speeds up I would say your good to go, and move on to other items on your list.... hope this helps some🙂
Thank you so much!
I did some adjustment on bias using your guide. Now the DC offset droped down to ~25mV on both channels, signal on scope is very nice. The third pot I did not touch very much, but it seems to be for the rail Voltage, its at 46 volts, if I remember right (check that later again).
I solved the problem with the fan running at full speed all the time by inspecting the board. I found a defective TIL192A optocoupler. I could not buy the TIL192A here in germany and found no sub for it (any tipps?). So I bought one on ebay in the UK. Soldered that in, and now the fan is speeding up at power-on, but slowes down after some time. I think thats correct now. Will heat up the heatsink and watch the fanspeed.
I don't have any schematics or other technical data for this amp, but it works fine now.
Thank you again for your help *thumbs up*
I did some adjustment on bias using your guide. Now the DC offset droped down to ~25mV on both channels, signal on scope is very nice. The third pot I did not touch very much, but it seems to be for the rail Voltage, its at 46 volts, if I remember right (check that later again).
I solved the problem with the fan running at full speed all the time by inspecting the board. I found a defective TIL192A optocoupler. I could not buy the TIL192A here in germany and found no sub for it (any tipps?). So I bought one on ebay in the UK. Soldered that in, and now the fan is speeding up at power-on, but slowes down after some time. I think thats correct now. Will heat up the heatsink and watch the fanspeed.
I don't have any schematics or other technical data for this amp, but it works fine now.
Thank you again for your help *thumbs up*
Hi,
I own a Zapco studio 500 limited edition and i'm looking for schematic diagram (service manual). i suspect there is a problem with the "Sig Ref" .
Can anyone help me to find it? it seems is hard to find untill now i didn't find anything.
Thanks a lot
I own a Zapco studio 500 limited edition and i'm looking for schematic diagram (service manual). i suspect there is a problem with the "Sig Ref" .
Can anyone help me to find it? it seems is hard to find untill now i didn't find anything.
Thanks a lot
Zapco has been releasing some of the older amp schematics. Have you tried contacting them?
If you have questions or need help with a repair, please start a new thread.
If you have questions or need help with a repair, please start a new thread.
ok Perry Babin, thx a lot for your answere, i will try to contact them and i will open a new topic too if i didn't find any solution.
i can hear everything happen in my car electric wiring, i means when i switch on the engine, (i hear the electric fuel pump before switch on), and also i can hear a little the alternator. Just yesterday night i discovered it is possible that the cable are too close to the car electric wirings. i also tried to connect the head unit ground to the sig ref of the 2 zapco. Actually the sig ref is connected to the negative of the macrom then go to the Zapcos. Following the Zapco instruction i connected the head unit metal case to the sig ref but nothing change. may be i have a problem in the both Amps this is why i'm looking to buy the manual service to see if i broken any electric component in the sig ref circuit
my system:
Head unit: Alpine 7990r F1 status
Cross over: Macrom 48.13
Sub woofer Amp: Zapco studio 300X
Woofer Amp: Zapco studio 500 limited edition
Mid + Tweeter Amp: Audison LRx2 250 W
speakers:
Sub woofer: JL Audio 12W6v2-D4
Woofer: Focal 6k2p (2for each door)
Midrange: AD M40 neo
Tweeter:Technology LS29 neo
my car BMW330CD
my system:
Head unit: Alpine 7990r F1 status
Cross over: Macrom 48.13
Sub woofer Amp: Zapco studio 300X
Woofer Amp: Zapco studio 500 limited edition
Mid + Tweeter Amp: Audison LRx2 250 W
speakers:
Sub woofer: JL Audio 12W6v2-D4
Woofer: Focal 6k2p (2for each door)
Midrange: AD M40 neo
Tweeter:Technology LS29 neo
my car BMW330CD
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