Hello Ron,

Succes and see you later,

Bertus

 

Hello Ron,

Succes and see you later,

Bertus

I'm having success with C18, C20, C55 & other capacitors that are in series, but having problems with readings, like the resistors, when they are in parallel with other components, but the main things seem OK.....I'm wondering if I'm just going too deep and would have to unsolder capacitors to check them.........it may be time to just put my TR8 & TR10 back on the board, check for obvious shorts, then try to power it up and see if the fuse holds....if it does we can get into voltages and current for further checks if needed...

 

So it's not fixed yet??

How many hours so far? And people wonder why it can cost $200+ to repair a power amp...

 

So it's not fixed yet??

How many hours so far? And people wonder why it can cost $200+ to repair a power amp...

Repairmen deserve, make their pay, and provide a valuable service.

Just briefly, I have a disability(CFS), after 33 years as a land surveyor, can no longer work, and refuse to become useless, thus my search for "knowledge" for my hobby, which is done mostly from bed, when I'm able.

Bertus should be commended for being the most helpful person I've encountered on this forum, for his patience, time, style of teaching, etc...
If one reads his "quote" and posts, one understands that this forum is well served by "positive help", which is why one would seek forum members for DIY info...
Anyone without adequate knowledge that wants repairs ASAP gets a professional, pays, and doesn't question why, or how......gets his needs served, and would not be on this forum.....but many inquiring minds are here to learn. If my amp never turns on, I will still have learned many aspects of electronics, which has helped me to do many other simpler repairs.......BUT.....I will not give up the quest....

 

So is it fixed or not.
I did not go thru all the replies, but read the first post.
If not fixed, if you are up to it, then I can help to get it up and running.
I'm sorry I missed this thread

PS. Did you know there is a way to power amps without (blowing fuse) or destroying any other component even if the out put stage has a shorted component

Rifaa

 

So is it fixed or not.
I did not go thru all the replies, but read the first post.
If not fixed, if you are up to it, then I can help to get it up and running.
I'm sorry I missed this thread

PS. Did you know there is a way to power amps without (blowing fuse) or destroying any other component even if the out put stage has a shorted component

Rifaa

Current status: No, it's not fixed right now...preamp is confirmed to be working to FX out, with TR8 & TR10 removed, not blowing fuses...haven't found any other bad components yet......I'll surely listen if you have something to add.....hoping to learn also if you have any tricks up your sleeve.(you may want to read the whole thread to get the complete picture of what's transpired)...Thanks.... The other great thing here is meeting people from all over the world...islands in the Indian Ocean, now that's a new contact.....Great!!

 

Hello Ron,

Thanks for the credits.
As for the capacitors, it is best to take them out for the check.
Inside a circuit there can be components that disturbe the measurement.
Be sure they are discharged before measurement.
Some meters will not like capacitors with some charge in it.
For the electrolitic capacitors, they can have tollerances upto 20 %.
So the 100 μF can measure anyting between 80 and 120 μF and still be good.

Greetings,
Bertus

 

Hello Ron,

Thanks for the credits.
As for the capacitors, it is best to take them out for the check.
Inside a circuit there can be components that disturbe the measurement.
Be sure they are discharged before measurement.
Some meters will not like capacitors with some charge in it.
For the electrolitic capacitors, they can have tollerances upto 20 %.
So the 100 μF can measure anyting between 80 and 120 μF and still be good.

Greetings,
Bertus

I'm thinking that might be overkill at this stage to remove capacitors as there's not much room to work with this still hooked back up to the power supply, and I've already taken that out a while back and not wanting to go that far back unless necessary. I'd like to think more on the lines of installing TR8 & TR10 and do some resistance measurements and calcs, check for potential shorts, and if it looks good I could power up and see if it holds, recheck voltages and current.
Is that reasonable....?

 

Hello Ron,

When checking the transistors, take special care of TR4 and TR7.
(when both are defective TR9 will probably aslso be defective)
Of course TR7 acts on TR8 and TR4 acts on TR10.
When those have a short in Collector-Emittor, full current will be send into the endstage.
This should have the current limiting transistors TR11 and TR12 activated.

Greetings,
Bertus

 

Hello Ron,

When checking the transistors, take special care of TR4 and TR7.
(when both are defective TR9 will probably aslso be defective)
Of course TR7 acts on TR8 and TR4 acts on TR10.
When those have a short in Collector-Emittor, full current will be send into the endstage.
This should have the current limiting transistors TR11 and TR12 activated.

Greetings,
Bertus

Thank You...I'll take special cautions there to check all these points before and after installing TR8 & TR10, and before any power is applied.

 

Ron,

Just to see if any of the caps are bad, try and look for any "bulging" caps visible. Usually the electrolytic or tantalum caps have a flat surface on top but if they go bad sometimes they can bulge outward. Note that I didn't say bulging as in width, but just at the top of the caps.

 

Ron,

Just to see if any of the caps are bad, try and look for any "bulging" caps visible. Usually the electrolytic or tantalum caps have a flat surface on top but if they go bad sometimes they can bulge outward. Note that I didn't say bulging as in width, but just at the top of the caps.

thanks....no visible problems...

 

Baby steps.........still testing "prior" to installing anything so I'll have a reference when TR8 & TR10 do get installed......C18, C55, C60, etc...and D4, D5, etc..., resistors all reading OK........

Now to transistor measurements - study says they should measure 1 way only(polarity) from B-E, B-C, open C-E(either way)...correct..?

1) TR4-TR8 all meas correctly from B-E, B-C on the board, but there are readings from C-E(not shorted like my TR8/TR10's), which is because they are still in the circuit..connected on the PCB....correct......?

2) Even the brand new BDV64's, BDV65's(never installed) have reading 1 way from C-E...... is that because they are the Darlington pairs vs simple transistors.........?

3) TR9 has readings both ways B-C, B-E, one way C-E(still no shorts), while on PCB, still without TR8 & TR10.........not sure what I should expect with that circuit........

Need some clarification/explanations on each of these situations.....before I add components.

 

Hello Ron,

You are correct about the BDV's.
When you look at the datasheet of mospec, they show some extra resistors accross the B-E connection and a protection diode accross the C-E connection.
(see datasheet).
Usualy I search for datasheets at ICMaster.
They have datasheets from several suppliers.(other do not show the diode on the BDV's).
http://www.icmaster.com/

As for TR9 there are rather low resistors accross it, making the reading odd.

Greetings,
Bertus

 

Hello Ron,

You are correct about the BDV's.
When you look at the datasheet of mospec, they show some extra resistors accross the B-E connection and a protection diode accross the C-E connection.
(see datasheet).
Usualy I search for datasheets at ICMaster.
They have datasheets from several suppliers.(other do not show the diode on the BDV's).
http://www.icmaster.com/

As for TR9 there are rather low resistors accross it, making the reading odd.

Greetings,
Bertus

This might make a lot sense in that a power surge, etc...... may have shorted the internal diodes across C-E in the 2 major power transistors TR8 & TR10(BDV's), which is the protection that may have saved the rest of my components.
These diodes were the weak link "by design"......

As for TR9, are you referring to R73 & R74 affecting readings while testing on the PCB, still in circuit......vs. testing if it were off the PCB(not in circuit)..?

 

Hello Ron,

The protection diodes are of use when driving inductive loads.
This can be motors or relays.(the transistors are also uses for driving them).
The diodes protect the transistors against back emf of the inductive loads.

Greetings,
Bertus

 

Hello Ron,

The protection diodes are of use when driving inductive loads.
This can be motors or relays.(the transistors are also uses for driving them).
The diodes protect the transistors against back emf of the inductive loads.

Greetings,
Bertus

Please comment on my last question regarding TR9, R73, R74...?

 

Here is the trick I use when it comes to power amps.
Mainly for transistor output stage.

If the out puts are blown, then of course one needs to check the bias and drivers for shorts, and low value resistors for open circuit, if found any replace them, for caps I only check the bootstrap caps, if no other caps are bulgy but I am comfortable replacing it.
After checking them and renewing any faulty ones, the supply is checked with amp disconnected.
If the supply is OK, I replace the both the rail fuses with around 22Ω 5W resistors.
Remember to ground the amp input, to block any voltage at the input, bringing the amp to idle state.

Connect the voltmeter at the speaker terminal and just power up.
If everything is OK, the meter will read 0V with in seconds, and the resistors which are used as the fuse should not heat up.

If any thing is wrong, you can get a meter reading, even 1V is not acceptable, and also if the resistors heats up then there is a fault.
Using resistors provides a safety current limit if any of the out put is over driven and will prevent any thing from burning up.
Of course you should be quick to disconnect the power if the resistors are getting heated up or if the meter reading is anything other than 0V.

If a fault is indicated then from there one have to take the bias readings with the resistors still in place, the resistors can only be taken out once the amp is OK at idle and the biasing does not change after warm up.
The best part of this method is that the amp can be driven at a low input level and the speakers connected.
Remember not give too much input with the resistors connected, as it will drop voltage if you try to drive the amp at high volume and will burn the resistors.

This is a proven method I use and has always worked for me

Rifaa

 

I will keep this procedure in mind(saved in forum of course), but it's a little above my knowledge to test bias(haven't got that knowledge yet), so I'm going to continue on my long, slow, methodical process of testing components until TR8 & TR10 are safely(after confidence in all output components tested) aboard(which would need to be before I could utilize your method). If I still have problems with my method.....I will have to learn about bias and how to use your process........that's very valuable information......and would open my mind to more knowledge required.

The point I'm dealing with now is understanding the readings to expect measuring transistors, using diode mode on my digital multimeter, "while transistors are still in circuit" vs. off the PCB.....learning what to expect for readings to be sure they are operable(no shorts is a good thing)....what can be determined without removing them......?

 

You know,
Semiconductor in circuit testing is not reliable, although if you checking for shorts is OK, but what if you get a reading from both ways in a diode, only experience can tell if they OK, best way is to disconnect one pin, same goes for transistors.

Resistors tend to give abnormal reading in circuits if there are charged caps, u know.

Anyways, meddling with it can give you experience.

I advise to use my method to test your amp, post back and I will guide you through biasing and all.

Rifaa