Hot Rod Deville low output Power amp out is strong

[gbono]

Just saying, if you tighten the black screws first and then snug down the front panel hardware - not so good.

ribbon cable connections?

start from input jack as Enzo suggests and check signal integrity going forward - same for power amp signal chain.

Maybe the thing is cursed and you will need an exorcism - getting close to Halloween..........

[lo-watt]

Just saying, if you tighten the black screws first and then snug down the front panel hardware - not so good.

ribbon cable connections?

start from input jack as Enzo suggests and check signal integrity going forward - same for power amp signal chain.

Maybe the thing is cursed and you will need an exorcism - getting close to Halloween..........

Ribbon cables have been replaced. I only have a multimeter at this point.

[gbono]

build and audio "sniffer" to listen to the signal applied at the input (lot's of test tones on the web) - you use a small audio amp/speaker and a probe using a capacitor with appropriate voltage rating..........

[Enzo]

OK, this is important. Troubleshooting is about the circuit, not the parts. Pulling the input jack to see if it works doesn;t do it. It only matters what the jack does in the circuit. You put a signal into it with a cord, then you follow that signal. If both input jacks produce no output, it really is pretty unlikely both failed as you put the amp together. So plug a signal into the jack - pick one - then see if it is present at the grid of the input tube. If yes, then move to the plate of the input tube. From ther the signal path splits in two, and since we have neither channel making sound, I tend to think both channels are not defective in the same manner.

If the signal does not reach that first grid, then check to see if it is on the 68k resistor to the jack in use. When I said the jack was suspect, it wasn't because I thought necessarily the jack itself was broken. It could be. yes, but It could just as easily be that the copper trace on the board had been cracked near it. That can happen from the force of remounting the board for example.

Work in the clean channel. You could do either, but the dirt channel has more stuff. I'll bet my lunch money that if you cure the clean channel, you will find the dirt channel now working too. Moreover, since both channels are quiet, we look for other common areas. the first is the pre volume relay K1a. So if that died we lose both channels. So if we have signal at the plate of stage 1, then do we see it at the next grid?

From there we go through the tone stack, so could we have broken or cracked the treble control?

[lo-watt]

I dont have any other tools at this point than a Fluke dvm. That being said, i checked continuity from the jacks to the next stage. The relay is the one place i had not checked. I can check the NO and NC contacts and other connections in it. Ill sub some Switchcrat jacts in too just to see. I have checked abpit every trace in the preamp for continuity. Found no issues.

[lo-watt]

Also checked all the pots for proper value and operation. They all test good from 100-0-100.

[52 Bill]

Too many questions and no clear answers. If you plug into the power amp in jack is there signal?

Agree with Enzo, stop trying everything and look for the problem. Test things to isolate the problem and fix it.

[lo-watt]

Too many questions and no clear answers. If you plug into the power amp in jack is there signal?

Agree with Enzo, stop trying everything and look for the problem. Test things to isolate the problem and fix it.

No thete is no signal there

[52 Bill]

If you test the dc voltages on the driver and output tubes how do they compare with the schematic values?

[lo-watt]

If you test the dc voltages on the driver and output tubes how do they compare with the schematic values?

The factory schem requires a 1khz sine wave to get TestPoint voltages. I don't have a signal generator. I've had to make best guesses in most cases. I've been reading DC voltages in the usual areas and nothing seems out of place.

[olddawg]

Dude ... You are being stubborn. Get an iPod or something (I used to uses the rec out of my bench amp), shove some signal into the main amp in. Got volume? If not use your DVM on the AC scale to signal trace. If the output is fine plug into the input Jack and start tracing the signal with your DVM. It's all you need. If you think it's easier use any amplifier and a cap to make a signal tracer.

[J M Fahey]

Hereīs a 30 second 1kHz MP3 sinewave tone.

Play it through Smartphone/Notebook/$10 MP3 player

Any of them will supply some 200mV RMS through the headphone out.

Make a stereo 1/8" plug to mono 1/4" guitar plug cable, any convenient length, join both right and left phone out channels, I have never ever seen damage caused by that

http://www.mediacollege.com/audio/to...6bit_30sec.mp3

Measure audio voltages with any multimeter.
Some are not too good at 1kHz and above, but all reach around 400Hz well; if suspect use this MP3 instead:

http://www.mediacollege.com/audio/to...6bit_30sec.mp3

It lasts 30 seconds so set player to repeat/loop/"repeat one" to have a continuous tone.
You will probably have a small "chirp" or interruption, about 1/4 second every 30 seconds, when tone ends and restarts, no big deal.

Inject in the input jack and follow the udio pth.

You canīt measure straight at plates because you have 100/200V DC there and that will drive the multimeter crazy, but plates are connected to next stahe grids, or tone or volume pots hrough caps, so measure after them, no DC across pots in a healthy amp.
If you have to measure at some plate and have no convenient coupling cap, invent a load: connect plate to a grounded 1M resistor , through a .022 or .047 x 400 or 600V plastic cap (poly-something)

Didnt check the schematic but I bet all audio test TPs have audio but not DC but if one has DC, I suggested how to measure anyway.

If you plain put a cap in series with multimeter probe, the short spike might drive it crazy, not sure about possible damage, but if you creat a load as suggested, itīs safe to measure.

A good multimeter with 200mVAC/2VAC/20VAC and so on scales is best but even a cheap one, those with only 200 and 500/700 VAC scales can read values around, say, 5VAC and over.
Donīt even ry to measure, say, 100mV or anything under 1V because they wonīt "see" them.

[nickb]

You can even get a free Oscilliscope for your mobile device e.g https://play.google.com/store/apps/d...roid.osciprime - you need to build an attenuator (add back to back limitung diodes for safety) for the mic input - first ring on the headphone/mick jack.

Plus there are a ton of signal generators https://play.google.com/store/apps/d...rator&hl=en_GB

[lo-watt]

Today i am leaving for the beach and will be gone until Sunday. So i'll look at the issue with fresh eyes Monday morning. The customer is being cool about it and has other amps to use. Im going to have to put about another hour into it,as i have lots of other guitars and amps to work on and i cant just devoted all my time to this one.. Hopefully i can systematically start from the input and work my way forward. After this job is finished,I'll see about getting or making a signal generator,but for now ill have to get through this job with just a DVM.

[lo-watt]

Well.the customer decided not to continue with the repair. I had assured him,I would not charge for the diagnostic time i was putting in,I was really just curious to find out what the problem was. He had already purchased another amp and was going to sell the amp AS IS on the internet. SO I did not get to find out the issue. It was my hunch that it was minor and would have been found sooner rather than later.

It did however expose that i need a signal generator(not on my phone or my ipod,these are cheap enough on eBay and is a tax writeoff). I have a Tektronix scope,but am looking for a Fluke 123 to keep in the shop when basic DVM is not going to cut it.

I have enough other jobs in house to fix,gotta put this one behind and look at the next one.

If any of you have anything to add,please do,I love all of the responses from the pros on here!