Ecler PAM 1360E Module Current Fault

[paul_g_787]

Hi Everyone.

So The PAM Ecler 1360E is now functioning, however the CH2 Power Module heat-sink gets very hot to the touch, but the CH1 Module doesn't.

Using information from the 'SETUP' procedure on page 44 of the manual available here:
https://elektrotanya.com/ecler_pam1360e_pam960e_pam560e_pam360e_amplifiers.pdf/download.html

I have removed each fuse (+90VDC rail and -90VDC rail) for each module in turn and connected my ammeter in it's place.

Channel 1 Module, both fuse holders give me a reading of 210mA
Channel 2 Module, both fuse holders give me a reading of 460mA

This of course explains why the channel 2 module is noticeably warm when idle and ch1 is not.

The service manual says each module should read 420mA. I am however confused here as to which module is at fault.
Does it mean 420mA  for +90VDC and -90VDC rail independently, so 210mA on each, Or 420mA on each but that would be 840mA per module?


So the question is which module is at fault?
Is channel 1 not drawing enough or is channel 2 drawing too much?

I have checked for shorts on all 3 pins of all power transistors on both modules and cannot find and issues there.


To note:

• The amplifier is operating fine, and I get sound out both channels.
• The 5K CURRENT resistor on each module is set to the same value on both modules, it appears to be factory set still due to the red paint splodged on the resistors.

[timenutgoblin]

Apologies for removing my previous post...

I also think that both amplifier modules are faulty, i.e., CH1 is under biased and CH2 is slightly over biased.

According to the Service Manual, you should be measuring 420mA (the limit is 0.8A) through each fuse holder. Since the power supply rails are connected in series and not parallel (i.e., +/- 90VDC is equivalent to 180VDC) then you should be measuring the same current in each fuse (i.e., per amplifier module). Current flows from +90VDC rail through the first fuse, then the positive half of the amplifier (module), in to ground, out of ground, through the negative half of the amplifier, through the second fuse and finally the -90VDC rail. 

As a first step, you should (could) try adjusting the Vref as outlined in the "TEMPERATURE STABILIZING CIRCUIT" section of the Service Manual in an attempt to adjust the bias current for both amplifier modules.

Is it possible for you to adjust CH2 amplifier module to measure 210mA for each fuse holder - the same as CH1 amplifier module? If so, compare the temperature of both amplifier modules (CH1 and CH2) after they have warmed up.

[paul_g_787]

Do you think the mains voltage is affecting the bias current? The manual specifies a variac set to 230V, but my mains supply voltage was at 245V when I took this readings.

The +90VDC and -90VDC rails are actually at approx +95VDC and -95VDC

How would this affect the bias current? Would it go up or down?

Reminder that CH1 is 210ma and CH2 is 460mA and this is stable after approx 10 seconds and also after a couple of minutes and doesn't even fluctuate by 1ma, but CH2 is definitely getting much hotter (which makes sense)

I do not have the luxury of owning a variac so I just have to use whatever voltage my mains supply is. Maybe one day I can afford one

[timenutgoblin]

Do you think the mains voltage is affecting the bias current? The manual specifies a variac set to 230V, but my mains supply voltage was at 245V when I took this readings.

The +90VDC and -90VDC rails are actually at approx +95VDC and -95VDC

How would this affect the bias current? Would it go up or down?

Does your mains (AC) supply voltage fluctuate at all or is it always stable, 245VAC? If it fluctuates, how low or high is the measurement? By my calculations, 245 / 230 x 90 = 95.87 which agrees with your DC rail measurement.

I think that the bias current should change in direct proportion to the DC supply rails. I think that's why they specify 420mA per module at 230VAC test voltage.

Reminder that CH1 is 210ma and CH2 is 460mA and this is stable after approx 10 seconds and also after a couple of minutes and doesn't even fluctuate by 1ma, but CH2 is definitely getting much hotter (which makes sense)

Do you have a thermometer? How hot is CH2 amplifier module? What about CH1 amplifier module?

I do not have the luxury of owning a variac so I just have to use whatever voltage my mains supply is. Maybe one day I can afford one

You may not necessarily need one for this, but it would be useful.

[paul_g_787]

Does your mains (AC) supply voltage fluctuate at all or is it always stable, 245VAC? If it fluctuates, how low or high is the measurement? By my calculations, 245 / 230 x 90 = 95.87 which agrees with your DC rail measurement.

I think that the bias current should change in direct proportion to the DC supply rails. I think that's why they specify 420mA per module at 230VAC test voltage.

Ah that makes sense then.  So would 460mA be in the ball park for 245V supply?

Do you have a thermometer? How hot is CH2 amplifier module? What about CH1 amplifier module?

Yes, my multi-meter has one that I can tape to the heatsink. I will do this and take measurements and post back.

[paul_g_787]

OK so I did a little experimenting. I connected my ammeter to CH2 and was reading spot on 460mA again, however my voltage today was 238V.

So it looks like it is not proportional to the supply voltage? Anyway I adjusted CH2's current resistor until the module was at precisely 420mA.

So I then connected my ammeter to CH1 and turned up the current resistor but the current went down and up and all over the place.

Upon further inspection I found that the current resistor had a dry joint! I re-flowed this resistor and everything important looking on the CH1 power module PCB.

Then I tried setting the current and it is all working great! Set it to 420mA same as CH2 and both are sitting there stable.

I am now measuring the same temperature on both channels. 

I have tested it with the speakers again and all good.

Thanks for all the helpful tips!! I am still learning and all of this is so helpful.

[timenutgoblin]

OK so I did a little experimenting. I connected my ammeter to CH2 and was reading spot on 460mA again, however my voltage today was 238V.

So it looks like it is not proportional to the supply voltage? Anyway I adjusted CH2's current resistor until the module was at precisely 420mA.

Okay, that's interesting. I am aware that (MOS)FETS have different operating regions corresponding to ohmic for low values of VDS starting from zero volts. IDSS (constant current) when VDS is above a lower threshold, but below a certain upper threshold where breakdown starts to occur (VBR). IDSS is usually specified at VGS of zero volts. It looks like your MOSFETs are operating in constant current region.

So I then connected my ammeter to CH1 and turned up the current resistor but the current went down and up and all over the place.

Upon further inspection I found that the current resistor had a dry joint! I re-flowed this resistor and everything important looking on the CH1 power module PCB.

Then I tried setting the current and it is all working great! Set it to 420mA same as CH2 and both are sitting there stable.

I am now measuring the same temperature on both channels. 

I have tested it with the speakers again and all good.

Thanks for all the helpful tips!! I am still learning and all of this is so helpful.

Glad that you found the issue/fault!