Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

sick amp please help

Status
Not open for further replies.

richa123

New Member
hi everyone, new here , hope i'm in the right place. i'll start with my first problem....., not a hi fi amp but a chip amp all the same, i have an indie sky 10 guitar amp (please don't laugh, i know it's a bit rubbish , all the same it does suit my purposes very well at the moment, problem is it's given up the ghost.., guitarist friend used it on a jam session a while back and it was used very hard all day,,, it then just stopped. he gave it to me (if i could fix it!!!!) to use in my home studio. even though its not great the overdrive channel sounded ...goood.
this is the problem.
1. it doesn't power up, no pilot light, no switch on thump or anything
2. there is no evidence of blown components, no burning at all and no damage to any components
3.i have checked the transformer, there appears to be no voltage at all from the power transformer, or any voltage anywhere on the board. (it did say .03 volts (ac at the transformer)????,
could it simply be power supply problem?
brief rundown
the amp is rated at 10 watts output, it uses tda 2050A chip
the power diodes are 1n4002 ( 4 of)
the transformer siply gives 4TZ-10, TY0603, cant find any info on this at all,.... i assume it is split rail ( red black red on the output side, any idea on voltages ??? (for replacement)
Please help!!!! the photos give you an idea of layout.
i have built ("from kits") a pair of maplin 50 watt mono blocks with uprated power supplies,(individual to each channel,) and a pre amp, they are rather goood, these are kit amps and i merely followed the instructions but when it comes to troubleshooting i'm a bit lost. could anyone give any help on the indie repair, there is no point buying anything else as i'm sure it must be a simple repair, anyway thanks in advance for any help you can give,,
 

Attachments

  • 065.JPG
    065.JPG
    644.6 KB · Views: 298
  • 066.JPG
    066.JPG
    643.2 KB · Views: 299
  • 067.JPG
    067.JPG
    670.6 KB · Views: 311
I am guessing that you are in the UK.

It sounds as though the fault is on the mains wiring or the transformer.
Try this:

1 Unplug it from the mains
2 Check the fuse in the plug
3 If it is a rewirable plug, take of the top and check the connections inside.
4 Use your meter set to the ohms range to see if there is continuity from the pins of the mains plug to the switch (both wires Line and Neutral).
5 Set the mains switch to ON, check to see if each pole of the switch is closed.
6 Check that there is continuity through the primary of the transformer.
7 Check that there is continuity through the secondary of the mains transformer (Unplug it from the circuit board first).

That should give you some ideas to start with.

JimB
 
i'll say the most likely problem is the transformer primary. you said your friend ran it hard all day, therefore it's likely the built-in thermal fuse in the transformer opened up. it's a common failure. another possibility with a "combo" amp (where the amp and speaker are in the same box) is that vibration from the speaker worked a solder connection loose on the board. but, since you said the transformer secondary voltage is 0V, i'll go with the primary.
 
It appears to have a fuse holder on the front panel (right end) and the fuse type information is printed on the back panel.
 
the fuse holder is on the PC board with a brown wire on one end a black wire on the other end. in the middle picture the fuse is in front of the input jacks and to the left of the transformer secondary plug. it's hard to see because the transformer secondary wires are in front of it.

this is a fairly standard amp design, probably 100 or so companies "make" amps with the same guts inside, with the only differences being the name on the label. actually what happens is that there's a manufacturer in the far east that has one standard design, and they contract with companies to manufacture the amps for them and slap the contractee's name on it. it doesn't matter if it says Fender or Sky or Line 6 on it, it's the same 10 watt practice amp inside (although Fender is a big enough gorilla in the market to get a different preamp circuit and maybe a barebones DSP board if they want one).
 
Last edited:
The fuse holder is on the PC board with a brown wire on one end and a black wire on the other end. In the middle picture, the fuse is in front of the input jacks and to the left of the transformer secondary plug. It's hard to see because the transformer secondary wires are in front of it.

I see it now. I guess what I was looking at was just the back of the power switch. The silkscreen on the board says F2. Is there an F1 somewhere?
 
probably no F1... as i mentioned these amps are "OEM'ed" for more than one company. maybe the first company to contract this chassis used an IEC socket on the back with a built-in fuse, and that would have been F1, and the one on the board would have been a backup (or "idiot-proofing") fuse. in other words, if you put an over-rated fuse in the IEC socket, and there was something serious wrong with the amp, F2 would blow, and the average user would not think to check inside for a backup fuse. all they would know is that they replaced the fuse in the connector, and the amp still doesn't work. if the IEC fuse were 1A, the backup fuse would be 1.25A, that way the IEC fuse blows first (unless of course, an over-rated fuse is put in the connector. the thermal fuse in the transformer serves a more basic safety function. much of the insulation materials in transformers have low melting points and are somewhat flammable compared to other components (in cheap transformers, mostly). the thermal fuse opens the primary if the temp gets high enough to assume that the wires further inside the transformer are hot enough to melt or char the insulation. the thermal fuse goes open, removing the source of current (which removes the heat source). the thermal fuse is usually inside the outside wrap of insulating tape on the transformer, although i have seen them near the core, inside the bobbin.
 
In the middle picture, the right hand column of the table printed on the back of the box seems to be headed 'Fuse Type'. That column should have data which will indicate how many fuses there are and what their types (e.g. quick-blow) and values are. There seems to be three fuses listed.
Locate all the fuses indicated and check if they've blown or popped out of their clips/holders.
 
Last edited:
actually, that's only a listing of what fuse to use at various line frequencies and voltages, not listing three different fuses inside the amp. this is very common when a single amp chassis is used in various markets. all the manufacturer needs to do is install the appropriate fuse, and wire the transformer primary for that voltage.
 
It's really common for the TDA2050 to blow up and go shortcircuited after hard use, that can cause a current overload that can take out the thermal fuse inside the transformer primary winding.

If you have access to a PSU, the TDA2050 typically uses +/-15v to +/-25v (max) so you can connect a 30v PSU to the amp instead of the transformer secondary, and check the amp still works and the TDA is ok.

It's also possible the transformer primary fuse just blew from heat and hard use and the rest of the amp is ok. Of if you are in the UK don't you have a fuse in the mains plug itself??
 
The OP was last here on the 26th July, perhaps he has lost interest in the amp.
Unless he returns, I think that there is not much point in further conjecture.

JimB
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top