XTANT 4180 4 channel

[joesch1999]

ok working on this amp replaced a zenner that was at 0.000, put two new 50v 1000uf caps power supply side and replaced a tip29c npn transistor, now amp powers up and produces audio just fine, it is drawing excessive current, showing 112 ohms probes across battery terminals, I am pretty sure it should be double that, obviously the power converter is showing the same, I should pull it, but it looks good, besides it looks like it has heated up some and moved a little from where the factory placed it, there is some black around a couple of the leads of the converter that connects into the board, I did clean them up and resolder them, the only thing that gets hot is the tip 29c when powering the amp up everything else stays relitively cool, should I go ahead and pull the converter/transformer or look elsewhere, it will stay on for a couple min then go into protection, it pulls 3 amps at idle with no speakers connected and goes up to four amps just before it goes into protection, the only reason I am questioning puilling the transformer is because of the delay it takes before it goes into protection does it sound more like another power supply cap, by the way there are two tip29c's only one of them gets hot, I have tried wiggling the transformer nothing changes, but it wont move much either.

[Perry Babin]

112 ohms across the B+ and ground terminals isn't enough to make it draw excessive current but if the resistance was constant, it may indicate that there is a problem.

If you reverse the probes, do you still get ~112 ohms?

How is the TIP29 being used?

When you stated that nothing was getting hot, were the transistors clamped to the heatsink?

[joesch1999]

I believe it's being used for switching between N and P channel,
well here is how they are placed n channel z44's 7 of them then 4 two legged voltage regulators byzq7, then the tip29c thats getting hot(I already replaced it) then a tip30c,tip29c,tip30c,tip29c, then irf530 two irf9234's then irf530 then tip29c in that order throughout the p channel

[joesch1999]

by the way when you reverse the probes in goes down to 64 ohms red on - black on +

I did take the supply out and straighten it over to where it was before there was nothing, melted together looked fine.

[Perry Babin]

Measuring the resistance between the legs of the TIP29 that's getting hot and the Z44s (leg 1 to leg 1, 2-2, 3-3), do you read 0 ohms between the TIP29 and the Z44s?

[joesch1999]

no it's oL where i get zero is between the tip29 and then two of the byzq7's regulators but thats only once the amp gets hot, turn it off wait a couple min and goes up to 20 mega ohms, i did scope those regulators and they looked good even after getting hot could it be a cap that runs between those and the 29c? between the regulators and the 29 is a .001uf 100v metal film cap and a a1207 transistor.

[Perry Babin]

The 2 legged components are rectifiers, not regulators.

The TIP29 may be part of a voltage regulator. If so, it may be normal for it to get hot.

Are you sure that there are 7 Z44s? There are generally an even number of power supply FETs and there doesn't seem to be any flyback supply (producing low voltage or driver voltage) that could be using a single FET.

You didn't take the 'supply' out. The power supply is made up of many parts. If you pulled the round, wirewound component nearest the Z44s, you pulled the transformer. The other wirewound component is the inductor.

IF you set the meter to diode-check and place it across the B+ and ground terminals (try it both ways), what do you read?

You should completely disconnect the amp from the power supply when doing this. I assume that you disconnected it when measuring the resistance.

[joesch1999]

6 z44's yeah took out the transformer been calling it power supply since i was a child I knew it was the transformer old habits never die. when I say hot it gets 85 celcius

[Perry Babin]

If you set the meter to diode-check and place it across the B+ and ground terminals (try it both ways), what do you read?

85C is hot but when it's on the heatsink, it will be only a few degrees hotter than the heatsink. Linear regulators run hot and in some instances will fail if not tightly clamped to the heatsink.

[joesch1999]

Red + black probe - .476 switched .214