Repair ZP120

I have noticed that the 4 diodes (marked with black stripe) do not give any Reading on my multimeter.

Update: removed almost all diodes from underside op primary side. Theyre all Good. Something I noticed is that all the 5 points of this winding in the secondary side are shorted together, is this right? 

Hello, im from Germany and need your Help.

These two capacitors are defective. do you know the data for these?

TH16001 and TH16002.

 

Thank You

Max

Hi guys, I own a connect amp that was plugged (by previous owner) in to 220v when switch was on 110 v.

I replaced the fuse, replaced the TVR14241 (mov) and i noticed that the TH16001 also cracked. I could not source the Sck054 needed to replace this part in my local electronics store, so I hardwired it for now, and everything works perfectly. 

Questions are:

- with normal use (no power surge, no wrong voltage), will the unit get damaged if I keep it like that? 

- is th16001 used in 220v setup, or is it for 110v only, and th16002 for 220v?

 

If it will Increase the lifespan of the unit, i will order the SCk054 online.

 

Thanks for this super interesting group discussion, got me already quite far!

The thermistors here are NTC (negative temperature co-efficient).  These will have a higher resistance when cold than once they warm up.  I’m not an expert but I think that the purpose is to limit the inrush current when the device is first plugged in.  These are used in most sonos devices that drive speakers.  Each of these has large capacitors that charge up, and which will draw large amounts of current quickly without the thermistors.  You may notice your lights dim a bit when you plug in a device without them.  I notice this dimming with the ZP120 Connect:AMP devices, and that’s with the thermistors working!

The thermistors are active in both 110v and 220v devices.

Update: removed almost all diodes from underside op primary side. Theyre all Good. Something I noticed is that all the 5 points of this winding in the secondary side are shorted together, is this right? 

 

The secondary winding has two separate coils.  The first is across three pins with a centre tap.  Within each coil (the first 3, or the second two pins), you should measure a very tiny resistance (under 1 ohm) between the pins -- this is normal for a transformer.  The short between the two coils is not normal.  You may have a short between the two secondary coils, or it could be ‘downstream’ of that.

I’ve fixed dozens of these devices and haven’t seen this particular problem before.  You can try to remove the transformer and see if the dim bulb stays bright.  If it does then the transformer is probably not the problem.  Be warned though… Getting that transformer out and then re-installed is a pain to do.

I replaced the fuse, replaced the TVR14241 (mov) and i noticed that the TH16001 also cracked. I could not source the Sck054 needed to replace this part in my local electronics store, so I hardwired it for now, and everything works perfectly.

If you cannot easily source a SCK054, there are similar devices available, eg:

1.  SCK054 Specs:
   Zero power resistance at 25 deg C = 5 ohm
   Max steady current at 25 deg C = 4 Amp
   Approx resistance at 25 deg C = 0.18 ohm
   Thermal dissipation constant = 17
   Thermal time constant = 33 sec
    
2. TDK B57235S0509M0 (RS Part number 467-614)
   ​​​​​​​Zero power resistance at 25 deg C = 5 Ohm
   Max steady current at 25 deg C = 4.2A
   Approx resistance at 25 deg C = 0.11 ohm
   Thermal dissipation constant = 9
   Thermal time constant = 60
    
3. Yageo NTD04-005M (Element14 order code 3770791)
   ​​​​​​​Zero power resistance at 25 deg C = 5 ohm
   Max steady current at 25 deg C = 4 Amp
   Approx resistance at 25 deg C = 0.182 ohm
   Thermal dissipation constant = 9
   Thermal time constant = 48 sec

Сould you please tell me the value and marking of the resistor R16021?

That looks like it is labelled “31B”.  EIA-96 says that’s a 2.05k resistor: https://www.hobby-hour.com/electronics/eia96-smd-resistors.php

I measured in circuit, and got 1k.  Perhaps it is in parallel with the one next to it.

Thank you! Yes, most likely it is really 2k.

Hi! I found some time to work on this project again. I had a blown 10 ohm resistor and a bad PWM, switched both and blew again. I saw some black marks on one of the yellow caps between the two big caps and replaced those with a new PWM and now the light bulb goes out. Yay. Still no white light though. I did not measure anything on the measure points on the secondary side though. Also these 2 transistors were getting quite hot (but I suppose that’s due to the missing heat shield, case).

I think these are for the 36v which should not be on at that time? -Edit: I now noticed that the other diodes are for the 36v rail- I replaced these 4 diodes (2 pairs that are using case as heat shield). Rectifier is also good, amps don’t seem to be shorted. My only thought at this moment is the feedback unit. Do these even go bad? I would love to hear some thoughts. I will do further testing as I did not measure too much because noticed the diodes getting hot. 

I wonder if you’ve misidentified some components.

The two “yellow caps” located between the big capacitors are not actually capacitors.  They are varistors (or MOV for metal oxide varistor).  These have high resistance, but as voltage rises their resistance drops.  In the event of a voltage spike, these shunt excess voltage away from the circuit, acting as protection devices.  If they are dead then it is very possible your device suffered a voltage surge.  If so then this is recoverable, but there may be multiple component failures.

You said that you replaced 2 pairs of transistors.  The first pair are transistors and you need matching components (part number K13A60D).  The second pair are not transistors - they are dual diodes (part number SBR10100).

When you say it ‘blew again’, how fast was that?  Was it right away, or only after trying to play some music?

The first two transistors you mention are part of the 36V circuit.  When the device is idle (or even playing at very low volume), the amplifier is run off of a 14V supply that comes from the central transformer (which is driven by the PWM).  Once the volume is turned up, then the 36V circuit comes on.  That is where these two transistors come into play.  They are switched via signals that come from the mainboard, through the riser board, then out the small plug in connector on the end of the riser board.  Since this is part of the 36V circuit, you should be able to get the device working (albeit perhaps without any audio being produced), even if these are damaged.

You need to know if the PWM and transistors are actually working or not.  If you use a multimeter in diode test mode, you can look between each pair of pins (eg 1-2/1-3/2-3/2-1/3-1/3-2).  You need to test all pin combinations in both directions.  You want to see either an open circuit, or a small voltage like 0.6V.  If you get any shorts then the device is bad.

Ideally, if you can get it running with the dim bulb, then you can check the back side for the various bias voltages.  There are test points marked for GND, 5V, 3.3V, 14V, and GND36/36V (the 36V points may measure 15V and that’s ok).  You don’t need the riser board or main board connected to test these voltages.