Input overload LED permanently ON

[Mr T]

Hi guys,

I just finished my second AMP4 and I am quite disapointed :

- the overload LED (J3 pin 1) is permanently on, although nothing is connected to the inputs. Same if I ground them.
- the relay is not clicking when shorting J5 & J6.
- consequently I cannot set the offset.
- I checked the voltages : Q10 reads 9,04 volts, and Q2 reads 5,07 volts, everything seems okay and keeps nicely warm.
- you can look at chip solderings here to tell me if anything is wrong : http://www.dcx2496.fr/photos/2nd_AMP4.jpg
you may want to compare with this one taken on the working AMP4 http://www.dcx2496.fr/photos/tk2050.jpg
Can't see any difference, apart from the fact I got a bit more skilled now

Any idea of what I should look for ?

Thanks for your help and Merry Christmas !
Mr T




Edited 3 hours after posting : for some reason, after measuring various voltages around Q2 the overload LED went off. Strangely enough
the temperature has raised drastically on both regulators Q10 & Q2 since, although voltages are within specs. The TC2000 chip gets pretty hot too, is that normal [?]
The TP2050 gets mildly warm.

I am really baffled by this now [xx(]

[Niiico]

Salut Thierry,

I had a similar problem with my AMP4. Overload always on and only noise on one output on which I couldn't set the offset...

So, I re-melt almost everything, I de-soldered the toroids, re-soldered 'em (it looks better even I'm sure it wasn't the cause) and while checking every component on the board I found that IN2B (TP2050 pin32) wasn't soldered correctly. Arggghhh! It was very difficult to see. I had to look at the pins from the side and even like that I wasn't sure.

Maybe you have a bad solder on one of the pins of the chips.

[Mr T]

Hi Nico,

After searching thouroughly on the PCB and checking every single voltage I come to the conclusion that either U11 or the TC2000 chip fried : HMUTE is permanently HIGH, which makes the LED permanently lit even when I short J4 pins 5 & 6. The amp is continuously muted, thus making DC offset impossible to check.

Allo Jan, are you there ?

Mr T

[Mr T]

Hi,

Back with some info : checked all the TC2000 voltages, everything looks within specs except VREF on pin 15 : 1,7V.

TK2050 voltages look alright.

I also checked the power supply current draw : 160mA at idle with amp muted is A LOT !

All of this associated with that weird TC2000 VREF AND the J4 HMUTE LED always on leads me to think that TC2000 is badly wounded [xx(]

I am now REALLY awaiting feedback from Jan.

Mr T

[Mr T]

Hi all,

Not good news from that ill AMP4 of mine.

As Jan doesn't anwser I decided to change the TC2000 chip. I took it from another kit waiting for assembly (yes, third AMP4 in a few weeks).

Things have improved in some manner : the amplifier now unmutes and relay clicks, then I can imagine the TC2000 was fried actually.

BUT....

Unfortunately I now have ANOTHER problem which makes me really angry : rail voltage is present on J1 output 1, which means the TP2050 has probably gone to heaven too as I have no shorts or bridge anywhere, unless you can see one :

http://www.dcx2496.fr/photos/2nd_AMP4.jpg

Output 2 is working fine with 3mV offset.

I am really unhappy today as I now have TWO not working AMP4s (remember, I took the TC2000 from the unassembled kit).

Mr T

[MediaMan]

Hi,

[}]
Mr. T. wrote:
----
the overload LED (J3 pin 1) is permanently on, although nothing is connected to the inputs. Same if I ground them.
- the relay is not clicking when shorting J5 & J6.
- consequently I cannot set the offset.
- I checked the voltages : Q10 reads 9,04 volts, and Q2 reads 5,07 volts, everything seems okay and keeps nicely warm.
----


I've got the same results on my AMP 4. Except, that Q10 shown 9.14 Volt (which does not really make a difference to 9.04). I recognize, that Q10 becomes really warm (not touchable for period longer than 5 seconds), TP2050 gets also more than hand-warm, and the REF Pin 15 on the TC2000 shows a few millivolts (about 3-4 mV).

Does somebody has an idea (or a proof) if my TC2000 is also blown up?
Or any other idea to cure the problem?

I've checked the soldering visually and with an Ohmmeter as well.

If TC2000 is dead is it possible to get a new chipset from Jan?
(He's not stating these parts in his shop as spare componets.)

Thanks for you help,
Udo

Progress is the transition of the primitive over the complicated to the simple solution

[djQUAN]

hey Mr T,

first thing I noticed on your PCB is that the holes of the vias on the left side of the chip aren't lined up to their pads. could be that somewhere in the board, there is a via or pad that is not conected to anything it should be? worth checking I think.

[MediaMan]

Hi,
I've thought, that my problem would be the same as Mr. T's.
I was wrong. When i found out, that the fuse of my Amperemeter was blown I found out, that the current drawn via J5 was only about 2 mA. Ref Pin 15 was still at 0 and the overload and mute LED's where lighting (not lightning , which means a different behaviour). Finally i checked the main rail and found about 35.8 Volt of the main supply. That was definitly to much. My transformer is RingCoil 120 VA with 2 x 12 V sec. Giving an idle tension of 26.8 Volt. This lead to the 35.8 Volt Idle Power on the main rail.
I've used a (inductive-capable) dimmer to reduce the input power and the Amp started immediately when closing Pin 5 and 6.
So I think it's of general interest, that an average 24 Volt sek. Transformer may lead to an overload of the AMP4.

Now it works, Hurray yippi yi yeah!

Btw, i couldn't find any definite proposal what Transformer to use to get AMP4 smoothly running.
Cheers, Udo


--------

Progress is the transition of the primitive over the complicated to the simple solution

[longitude]

MediaMan,

So your amp4 works, congratulation!

When we say Amp4 is suitable for 24VDC operation, it means if you use unrectified AC source, you should use ~18VAC transformer.
Cause after rectified, 18VAC, you can get ~18*1.414=25.452 VDC, minus ~1VDC drop on diode.