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Post subject: Hotrod Deluxe noise & blown caps
Posted: Mon Mar 02, 2015 6:13 pm
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Hello all! Picked up a blonde Hotrod Deluxe from a pawn shop the other day for $90. It reproduces sound with a guitar plugged in, but has a strained, mid range hum/buzz. The reverb doesn't work either. I first replaced the tubes with a new set just to see if that did anything. Same sound issue. I popped the back off to have a look and noticed the 22uF and 47uF caps are blown out/leaked. This makes me wonder what happened that resulted in the failure of all of these?

Anyone have any ideas? I can easily replace the caps myself, but if there is a bigger underlying issue that caused the failure in the first place, I would want to address that. Thanks!

Here's a pic:

ImageIMG_3557 by johnnymusepro, on Flickr

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Mon Mar 02, 2015 7:58 pm
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[youtube]r[/youtube]

The original caps are cheap IC (Illinois) and are made in Taiwan. I'd replace them with Sprague, or F&T caps. Mine blew in three months in my HRDlx. I dumped that amp about four years ago and started building my own.

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Mon Mar 02, 2015 9:15 pm
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Well, thats a screamin deal if you can fix it.
The caps just wear out. If anything else caused a short, too much ripple on the caps will shorten their life, But if that was the case, it would probably have already taken down the power transformer or the inductor, or the dropping resistors.
Since it still works, its probably just the caps. Go with the above recommendations for replacements. I don't think i've ever seen a blue cap in there. Is it original?
The reverb is solid state and runs off a different power supply. It also can have a problem with burnt and broken solder on the 5 watt resistors and the 1N5353 zener diodes. There should be 0 volts on pins 1 and 7 of the op amp where the reverb wires come in. You can measure the coils of the tank at those wires too.


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 03, 2015 2:23 am
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Musepro,

If you have no electronic skill , know how to solder and never work on amp , see a qualified tech ;

Hot rod is a very hard to work on , 'cause printed circuit to remove . Also if you do not pay attention to ribbon wires you may have slots of noise.

If there is no qualified tech in you area ,( we found more handy man than qualified tech ) try yourself .


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 03, 2015 6:50 am
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Thanks to everyone for the input! I have heard that Illinois Capacitors are cheap but wow, this amp is from around 2007; I wouldn't expect even cheap caps to just fail after a few years of use. I do have a good inventory Sprague caps and usually only stock quality components, though I did buy a bunch of Weber caps for some prototyping ideas. I'll go ahead and replace the faulty components and see how it goes. Thanks!

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 03, 2015 7:35 am
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Musepro wrote:
Thanks to everyone for the input! I have heard that Illinois Capacitors are cheap but wow, this amp is from around 2007; I wouldn't expect even cheap caps to just fail after a few years of use. I do have a good inventory Sprague caps and usually only stock quality components, though I did buy a bunch of Weber caps for some prototyping ideas. I'll go ahead and replace the faulty components and see how it goes. Thanks!


JT keep us posted. Like I said, my IC caps failed on a brand new HRDlx after only three months.

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Mon Mar 09, 2015 8:51 pm
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Hi guys, back with an update.

I replaced all of the main filter caps with F&T and went ahead and replaced all of the 16VDC power supply filter caps with new Spragues. The two 5W resistors in the 16V supply had lifted some of the PCB pads due to the excessive heat they dissipate and the fact that's its a very cheap, thin single sided PCB without through hole plating. I replaced those as well, mounted on a bit of silicon to get them off the PCB and made a few hard wire jumpers to circumvent the ruined PCB pads.

The amp now fires up quietly and sounds great! But, still no reverb....

I had hoped replacing the 16V caps, the 5W resistors and repairing the heat-damaged PCB would fix the reverb, but it doesn't. Turn the reverb knob up and smack the tank, you'll hear the springs boing, so it looks like the reverb return works, but not the send. I gathered that opamp U2 was used as the reverb driver on one half and the return on the other, so I installed a new TL072CP opamp. I replaced the 5353 diodes while I was at it, since the PCB was scorched around their leads as well. Still no reverb.

Any thoughts on why the reverb still isn't working?

[url=https://flic.kr/p/reH2Xz]Image

[url=https://flic.kr/p/rvJFXU]Image

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 1:38 am
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You do good job .

Check contacts on " Power Amp In " jack, bypass them of not sure . Often dirty
Check C13 , follow this signal path .

'Scope and audio signal generator may help to see where the signal stop. Did the signal go to the reverb pan ? Or stop before ?

If go to the reverb pan , check reverb pan input transducer


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 9:52 am
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If you don't have a meter, swap the reverb leads on the tank. Turn the amp on, turn up the reverb and smack the top of the tank again.
This will tell you if the coil on the driven side is intact. If there is no sound, inspect the tank wires. Gently tug on each end of the green and black wires to see if they are broken.

If there is sound, then its possible that the reverb control is damaged. Pull gently on the reverb knob. If it pulls out more than a few thousandths or significantly more than the other controls it is damaged and not making wiper contact.


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 11:01 am
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I'm sorry, I do have a meter. There is no voltage on or across pins 1 and 7 of the U2 reverb opamp. I was getting -16/+16 on pins 4/8 with the old opamp, which made me think perhaps the opamp output faulted. With the new opamp installed, I still get -16/+16 on pins 4/8 and about 33V when metering across 4/8, so that still seems right. If I use pin 4 for reference, I get +16V on pins 2, 5 and 6, but only 8.4V on pin 3, which might be an issue. (pin 3 is fed through C13, which stratele52 brought up). The 16VDC PS seems to be fully functioning, as I can follow -/+48V to the 5W resistors and -/+16V out of the resistors and through the 5353 diodes and C40/41 caps to pins 4/8 of the reverb opamp U2.

Swapping the reverb leads gives me no sound when smacking the tank. When connected correctly, I get the spring boing. The pot feels good, not loose at all and I did wiggle it. The tank wires from the board to the tank are all sound and firmly connected. I don't see any obvious fault with the tank anywhere.

So far, I've only worked on vintage or vintage reissue tube amps using all tube circuitry. This is the first amp I've dealt with that has all this solid state in it. Despite the fact that I've built many studio equipment SS DIY kits (preamps, compressors, EQs) and have repaired some SS state studio equipment, I am not an electrical engineer. Still learning a lot as I go.

Thanks for all the input you guys have contributed so far. It would be nice to sort out this reverb issue and be able to call the amp 100% tip top.

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 11:50 am
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Musepro wrote:
I'm sorry, I do have a meter. There is no voltage on or across pins 1 and 7 of the U2 reverb opamp.
Not across , take reading from the ground

I was getting -16/+16 on pins 4/8 with the old opamp, which made me think perhaps the opamp output faulted. With the new opamp installed, I still get -16/+16 on pins 4/8 and about 33V when metering across 4/8, so that still seems right. If I use pin 4 for reference, Why ? Sorry no useful IMO , always from the ground I get +16V on pins 2, 5 and 6, but only 8.4V on pin 3, which might be an issue. (pin 3 is fed through C13, which stratele52 brought up). The 16VDC PS seems to be fully functioning, as I can follow -/+48V to the 5W resistors and -/+16V out of the resistors and through the 5353 diodes and C40/41 caps to pins 4/8 of the reverb opamp U2.

Swapping the reverb leads gives me no sound when smacking the tank. When connected correctly, I get the spring boing. The pot feels good, not loose at all and I did wiggle it. The tank wires from the board to the tank are all sound and firmly connected. I don't see any obvious fault with the tank anywhere.

So far, I've only worked on vintage or vintage reissue tube amps using all tube circuitry. This is the first amp I've dealt with that has all this solid state in it. Despite the fact that I've built many studio equipment SS DIY kits (preamps, compressors, EQs) and have repaired some SS state studio equipment, I am not an electrical engineer. Still learning a lot as I go.

Thanks for all the input you guys have contributed so far. It would be nice to sort out this reverb issue and be able to call the amp 100% tip top.


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 1:04 pm
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stratele52 wrote:
Musepro wrote:
I'm sorry, I do have a meter. There is no voltage on or across pins 1 and 7 of the U2 reverb opamp.
Not across , take reading from the ground

I was getting -16/+16 on pins 4/8 with the old opamp, which made me think perhaps the opamp output faulted. With the new opamp installed, I still get -16/+16 on pins 4/8 and about 33V when metering across 4/8, so that still seems right. If I use pin 4 for reference, Why ? Sorry no useful IMO , always from the ground I get +16V on pins 2, 5 and 6, but only 8.4V on pin 3, which might be an issue. (pin 3 is fed through C13, which stratele52 brought up). The 16VDC PS seems to be fully functioning, as I can follow -/+48V to the 5W resistors and -/+16V out of the resistors and through the 5353 diodes and C40/41 caps to pins 4/8 of the reverb opamp U2.


I did take all measurements from ground, which is what I mean by voltage "on". I only took readings referenced to pin 4 to see what I got. I didn't know if it would provide any useful info or not.

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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 1:30 pm
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Musepro wrote:
stratele52 wrote:
Musepro wrote:
I'm sorry, I do have a meter. There is no voltage on or across pins 1 and 7 of the U2 reverb opamp.
Not across , take reading from the ground

I was getting -16/+16 on pins 4/8 with the old opamp, which made me think perhaps the opamp output faulted. With the new opamp installed, I still get -16/+16 on pins 4/8 and about 33V when metering across 4/8, so that still seems right. If I use pin 4 for reference, Why ? Sorry no useful IMO , always from the ground I get +16V on pins 2, 5 and 6, but only 8.4V on pin 3, which might be an issue. (pin 3 is fed through C13, which stratele52 brought up). The 16VDC PS seems to be fully functioning, as I can follow -/+48V to the 5W resistors and -/+16V out of the resistors and through the 5353 diodes and C40/41 caps to pins 4/8 of the reverb opamp U2.


I did take all measurements from ground, which is what I mean by voltage "on". I only took readings referenced to pin 4 to see what I got. I didn't know if it would provide any useful info or not.


+1 ,

My poor english ....... :?

U2 pins 1 and 7 no voltages !!! Something wrong ; Ic bad or printed circuit open or there is a short to ground ?
Or some resistors to pin 1 and 7 have open circuit ?


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Tue Mar 10, 2015 7:09 pm
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If you swapped reverb connectors and got no sound, I would suspect a bad send coil in the tank. If you do have a meter, set it to ohms and measure the resistance of the two coils where their wires connect to the circuit board.
Look closely at these connections as the reverb wires are sometimes damaged when the circuit board is pulled out for servicing.
Measure from the conductor to shield of each wire. The send side is NOT grounded.
The red wire to it's shield should measure @70 ohms and the white wire to its shield @220 ohms.
I would expect the red wire to be open. If it is, do the same measurement at the tank connectors. If that's the right resistance, it's a bad connector on the red wire. If it's open, its a bad tank coil.

As far as the IC goes, measuring voltage from ground, only pins 4 & 8 should have any voltage. Since it's a new chip, it probably good and the voltage is coming from a leaky cap elsewhere.


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Post subject: Re: Hotrod Deluxe noise & blown caps
Posted: Wed Mar 11, 2015 7:22 am
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OK, looks like I found the problem. For the white wire, I get 58Ω across both the shield/conductor at the PCB and at the white tank input connector. For the red wire, I get no reading from the wire at the PCB OR at the tank’s red output connector. So, looks like I have a bad tank coil?

I do only get voltages on opamp pins 4/8, referenced to ground. There are no readings on the other pins. I only got readings on the other pins when I referenced pin 4. I didn't know if there was any value to taking a measurement like that, but I offered the info anyway.

Thanks so much for everyone's help!

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