New HT5-R - No Sound!

Discussion - HT-5 amplifiers.
BowerR64
Posts: 22
Joined: Sun Jul 19, 2015 5:08 am

Wed Jul 22, 2015 3:55 am

I know a little about electronics and a little about amps.

This amp has 2 transformers, they each have 2 taps or 3 taps?

It comes on and the preamp tube glows like my other amps. The power tube gets hot but i dont see it glowing but it could be shorted some one else mentioned or bad which i dont know symptoms of a bad tube.

Since the pre-amp tube glows and the power tube gets hot what does this tell me? Does the preamp run on a different part of the transformer as the power tube?

I have a meter and ive poked around on the power tube but im not sure of a few things. The heater lines should i be in AC or DC?

The schematics dont really say what voltage i should get, say S2, S3 and S5. then on the other S1 and S4

SP4, SP5 and SP6

Or on connector 1 that runs to the 12BH7, what do i test these with AC or DC? I just need to clip my _ probe to the chassis then test the voltage from connector 1-6?

BowerR64
Posts: 22
Joined: Sun Jul 19, 2015 5:08 am

Wed Jul 22, 2015 8:05 am

I dont seem to be getting any heater voltage

The 2 leads coming from the smaller transformer dont seem to be putting out anything.

The larger one seems to be working, i get 350V on the 2 outer leads SP4 and SP5, SP6 i get 63v but nothing out of it.

BowerR64
Posts: 22
Joined: Sun Jul 19, 2015 5:08 am

Sat Jul 25, 2015 2:53 am

ok i got in the new tube today, it glows normal but its still dead silent.

I tried 8 ohms from the 8ohm jack, a 16 ohm from that jack and 2 16s from those jacks nothing.

I then tried the headphone out only nothing using headphones.

I also tried from another amp the return i havnt put the end into another amp yet but i suspect it isnt going to work either.

I sprayed all the inputs and and out jacks, sprayed all the pots with deoxit i even pull and wiggle them when turning to see if maybe there is just a deadspot on any of them and nothing.

It really looks like it should work.

I dont hear any hiss or anything its just dead silent.

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thephantum
Posts: 1160
Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Sat Jul 25, 2015 6:20 am

The voltage will be very low at the output transformer when the amp is powered on and standby is off. So, you should measure something other than 0. If you are not, then the power amp most likely has an issue. It could be the output transformer itself, but since the emulated out is not working that means either the preamp is not working or the emulated out circuitry is not working or both. While it's possible the amp has multiple issues, it's much more likely that it's something common to multiple sections of the amp.

But that's not definitive proof that the pre and power amps are not working. It's possible that the just EO and channel switching isn't working. Even if you do some slave tests and nothing seems to work, it could be that the EO, channel switching and effects loop circuits aren't working. The only definitive tests would be to use a signal generator and o-scope to verify what is working and what is not.

I do not have the amp in front of me, so I cannot diagnose it. I can only make educated guesses based on the information you've provided. Only you have the amp in front of you so only you can diagnose it. Again, it might take a signal generator and o-scope to diagnose it properly. Those are expensive tools and the amp should go to a tech for that.

One possibility is if channel switching is dead, signal can't get from pre to power. Another is that the low voltage rails for lighting tubes and LED's are working, but high voltage rails to drive the preamp and power amp aren't. There are a lot of possibilities...but the most likely causes all point to the power supply. So you need to check the entire power supply, end to end, in methodical fashion starting with all the fuses (including the ones on the PCB), mains input, power transformer, rectifiers, chokes, step down resistors, etc, etc. Don't just check them visually or just check voltages...that will not tell you the whole picture. You need to check for resistance & capacitance, where applicable. Before you do that though, make sure you render the amp safe to work on by draining the caps first.

As I said before, my best guess is you have a bad PT. Again, measuring for voltage is not an accurate test. You need to test each winding for opens and shorts, both to itself and to the chassis. If you find something wrong with the PT, you still need to check the rest of the power supply circuit. For example, if there is a short in the HT rectifier it could have caused the PT to get too hot and develop an open/short.

I am not going to get into a step by step "How to diagnose your transformer" tutorial as I do not want to be held responsible if you or someone else kills/maims themselves or turns their amp into a 100% total brick. The fact is a step by step does you no good. To diagnose an electronic system, you need to understand what you are measuring, why you are measuring it and what each measurement means to both the component as well as the overall system. Otherwise you're just stabbing in the dark and will probably make things worse. You also need to make sure that you drain all the filter caps to render the amp safe before poking around with an ohmmeter. If you are not comfortable with any of that, you should really just take it to a tech. So proceed to the following link at your own risk.

http://www.geofex.com/ampdbug/pwrtrans.htm

416guitardude
Posts: 1
Joined: Thu Oct 08, 2015 8:14 pm

Thu Oct 08, 2015 8:36 pm

Hi, my first post here. I created an account just so I could respond to this post.

First off, HUGE thanks to jaded faith and everyone else here. My amp had the same problem and I've managed to fix it with your advice :) I have a few questions now and would be super-appreciative if anyone wants to chime in and answer them.

Quick background:

R38 was burnt, amp made almost no sound except for a few burbs and buzzes.

1) I used an exacto knife and scratched away between the posts of TR2. After that, the amp makes sound again, and at consistent volume but very distorted/ugly. (Scraping between posts seemed to work so I didn't bother drilling a hole.)

2) I replaced R38 with a 20kohm 2watt resistor. No change. Still sounded distorted/ugly.

3) I replaced TR2 with an IRF840 (couldn't find an 830). Now it's working :) Awesome! So I guess TR2 was damaged from the short.

So here are my questions:

A) The amp sounds WAY better, but on the clean channel when you turn it up past 12 o'clock, it gets mildy overdriven and quite overdriven on full. It's a fairly nice sound, but I recall this amp had more clean headroom than that. Am I misremembering how much clean headroom this amp has, or could there be some other component that I should inspect? (yes, will go to a store and compare)

B) I really am not sure if I used the correct resistor. The burnt resistor was reading 17.5k ohms, however it's color code could not possibly have been 17.5k. It was either red-black-unknown (20x) or it was brown-black-unknown (10x). Schematics I've seen had it at 22k ohm.. Anyways, it looked like red-black-unknown and I guessed the unknown was orange, and put in a 20k. Could wrong value resistor cause this extra harmonic distortion? Would it be worth experimenting with different values?

C) Those MOSFETs (t2 and t3) both get really darn hot. I can touch them, but hot enough that I don't want to leave my finger there. Normal?

D) As mentioned, I used IRF840 instead of IRF830. Could that cause any extra distortion or any other malfunction/safety-issue? Far as I know, it just has a higher max drain amperage and some specs otherwise...

Again, can't tell you how awesome it was to find this post and repair my own amplifier. Thanks to everyone for putting in the effort here and thanks in advance if anyone graciously answers my questions.

Cheers!

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thephantum
Posts: 1160
Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Fri Oct 09, 2015 12:05 am

A) The amp sounds WAY better, but on the clean channel when you turn it up past 12 o'clock, it gets mildy overdriven and quite overdriven on full. It's a fairly nice sound, but I recall this amp had more clean headroom than that. Am I misremembering how much clean headroom this amp has, or could there be some other component that I should inspect? (yes, will go to a store and compare)

The HT5 does not have a lot of headroom. Once you turn the clean volume up past about halfway, you will start getting output stage overdrive. So it's not only normal, I actually prefer it to the gain channel.

B) I really am not sure if I used the correct resistor. The burnt resistor was reading 17.5k ohms, however it's color code could not possibly have been 17.5k. It was either red-black-unknown (20x) or it was brown-black-unknown (10x). Schematics I've seen had it at 22k ohm.. Anyways, it looked like red-black-unknown and I guessed the unknown was orange, and put in a 20k. Could wrong value resistor cause this extra harmonic distortion? Would it be worth experimenting with different values?

It should be a 22K ohm. A 20k ohm could be close enough since most resistors have a +/-5 margin of error...but it depends on which way it's swinging. So I would try and put the correct value in there

C) Those MOSFETs (t2 and t3) both get really darn hot. I can touch them, but hot enough that I don't want to leave my finger there. Normal?

Yes. The level of heat you are describing is normal.

D) As mentioned, I used IRF840 instead of IRF830. Could that cause any extra distortion or any other malfunction/safety-issue? Far as I know, it just has a higher max drain amperage and some specs otherwise...

The 840 is essentially a "heavy duty" version of the 830. As you said, it can take almost twice the amperage. So, if anything, it's going to cause less breakup.

amp_guru
Posts: 1
Joined: Sun Nov 01, 2015 3:23 pm

Sun Nov 01, 2015 3:47 pm

I just repaired an HT-5 amp for a friend with the burnt R39 (22k) issue.
This website was super useful in suggesting that replacing the 22k was not enough and that the carbonized traces between TR3 transistor pins needed to be drilled out for a proper repair.

This is a great sounding amp and technically the R39 22k resistor was properly spec'ed.
It is a one watt unit dissipating less about 0.3 watts where power=Vr*Vr/R= (350-270)*(350-270)/22000

However, from a reliability point of view this amp is terribly designed.
The resistors cannot breath, since the PCB is completed enclosed in the chassis so that all heat is trapped and not vented. Over time the resistor heat accumulates, burns the PCB and creates carbon traces between the drain and gate. The MOSFET is a super high impedance device with 100 megaohms resistance between the gate and source.
So even if the carbon traces creates a pseudo resistor of a few megaohms, that is enough to forward bias (from the 270 volts present at the drain to the gate) the MOSFET and burn out the 22000 ohm resistor and sometimes the 10000 ohms resistor as well.

If I see this amp again for repair, I will take all the power resistors (22k and 10k) off the PCB and put them on terminal strips and wire them to the PCB. This is what Blackstar should have done as well as adding vent holes to the chassis. This few extra dollars of expense is much cheaper than the impact their reputation suffered from so many of these amps failing prematurely.

jerrydyer
Posts: 1
Joined: Wed Nov 11, 2015 10:21 pm

Wed Nov 11, 2015 10:48 pm

Ive had two of these over the years, the first one i could not fix for the customer because Blackstar and or Korg would not help AT ALL. Second one I was able to fix ONLY because Rob of Jaded Faith posted what he did. Thanks Rob. jerry from Surreal Amps.

pwyndham
Posts: 1
Joined: Thu Jan 28, 2016 4:07 am

Thu Jan 28, 2016 4:18 am

My HT5R just took a massive dump and is in the shop. I'm pissed because this happened a month after the 3year warranty expired and per other posts it appears it is pcb board short issues. I've loved the amp but won't be buying Blackstar anymore if it can't be fixed at a reasonable cost. Disposable amp business model Company may be Blackstar's business model, but I'm not gonna give them anymore money if the isn't resolved fairly.

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thephantum
Posts: 1160
Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Thu Jan 28, 2016 2:39 pm

If you read the posts you would know that this was a small batch of faulty boards from early 2012 that was corrected pretty quickly. After three years, how do you know the output tube didn't die and pull another component down with it? That is a common occurrence in catastrophic tube failures and not specific to any manufacturer.

Many times, when there is a manufacturing defect like this, a company will still honor the warranty. However, it has to be proven that the specific problem occurred and that the amp was manufactured during that impacted time frame. So have you even tried contacting Blackstar? Have you even looked at the date code on your amp? Or did you just register to bitch and moan in front of other owners?

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