Folsom's great little 7297 Chip Amp

KR500 · « **Reply #660 on:** 18 Oct 2016, 01:57 pm »

getting ready to power up but took a few pictures first .
I looked at the pcb power supply closely and although the negative and positive terminals are close together there is a distance between the two connections from what I could see. The terminals on the Antipole are a tad further apart and look okay .
Used stranded 16 gauge lamp wire from Antipole to pcb since my solid copper wire was so stiff.
With the meter probe on heat sink and pcb grnd I get the 000 readout and when moving to the power positive it starts as a number in the several hundreds and just keeps going up on the display

KR500 · « **Reply #661 on:** 19 Oct 2016, 06:04 pm »

Well , the LED and switch are working properly, but the meter is right in the continuity test as there is no amp output.
I've looked over the connections and am stumped as to where the circuit is closed.

lacro · « **Reply #662 on:** 19 Oct 2016, 06:38 pm »

Quote from: KR500 on 19 Oct 2016, 06:04 pm

Well , the LED and switch are working properly, but the meter is right in the continuity test as there is no amp output.
I've looked over the connections and am stumped as to where the circuit is closed.

Did you scrape through the mask on the top of your amp and expose the copper where you soldered your + connection on the amp board or is that just the wire sticking up through the hole?

Folsom · « **Reply #663 on:** 19 Oct 2016, 06:48 pm »

Looks like wire but could be cold joint.

Do you have voltage off of one of the OSCON caps?

drew_t · « **Reply #664 on:** 19 Oct 2016, 08:49 pm »

Why are carbon comps specified for the pair of 1K8s on the Antipole? Can I use 1 watt carbon films that I already have on hand instead?

Also, the indicated position for a resistor next to the row of diodes is for a discharge resistor, correct?

KR500 · « **Reply #665 on:** 19 Oct 2016, 08:58 pm »

I didn't know you had to scrape anything off the eyelets on the boards. I just pushed the 16 gauge stranded copper wire up from underneath and soldered to the terminal . The loose piece is a bit of the stranded copper . I used 16 gauge stranded and it was a tight fit so got messy on the positive side.
Yesterday I touched a probe to the heat sink and one to the positive leg of the pcb power and got a reading in triple positive numbers .
Not sure of how to check the Oscon with a DMM.
Do I have to have the unit plugged in to do this ? I'm assuming the Antipole caps got charged when I powered up today, not sure about the pcb caps ?

Folsom · « **Reply #666 on:** 19 Oct 2016, 08:59 pm »

No, use 1.8k not 1k. They're a specific value in relation to the CMC. They don't have to be carbon comp. Wattage can be higher.

And yes that's a discharge resistor location.

Folsom · « **Reply #667 on:** 19 Oct 2016, 09:03 pm »

Quote from: KR500 on 19 Oct 2016, 08:58 pm

I didn't know you had to scrape anything off the eyelets on the boards. I just pushed the 16 gauge stranded copper wire up from underneath and soldered to the terminal . The loose piece is a bit of the stranded copper . I used 16 gauge stranded and it was a tight fit so got messy on the positive side.
Yesterday I touched a probe to the heat sink and one to the positive leg of the pcb power and got a reading in triple positive numbers .
Not sure of how to check the Oscon with a DMM.
Do I have to have the unit plugged in to do this ? I'm assuming the Antipole caps got charged when I powered up today, not sure about the pcb caps ?

I assume they got charged too. But since they're connected already you're safe.

Reading of what?

Pick any OSCON capacitor and put a DMM lead on each of the legs. If you have 17.8v~ (or -17.8v~ depending on if you got meters backwards) then you've got power and should be good to go. If no, you can check the output of the antipole by putting DMM leads on the AUX outputs next to the big ones to check for voltage, to make sure you're good up to that point. And then you can check the incoming wires to the amp board too.

KR500 · « **Reply #668 on:** 19 Oct 2016, 09:17 pm »

okay Jeremy , thanks . I'll follow that and reply .
Reading of what?
Continuity Test on the Antipole output positive with no power to the unit

A dumb question , when checking the Oscon legs and Antipole terminals with the DMM probes.... that is with the amp plugged in to AC and switched on ?

Folsom · « **Reply #669 on:** 19 Oct 2016, 09:22 pm »

KR500 · « **Reply #670 on:** 20 Oct 2016, 05:24 pm »

I checked with the meter at the highest 600 setting in the VAC section, and then the lower 200 VAC setting and got readings of zero at the Oscon cap legs and also zero at the pcb power input eyelets.
Reading of zero at the Antipole power output , I couldn't reach the smaller eyelets with the probes so just used the soldered output neg and pos.
Checked again the wiring on the transformer for the jumper and outer terminals to make sure they are correct.
The power switch and LED work .

S Clark · « **Reply #671 on:** 20 Oct 2016, 05:32 pm »

You need to measure those Oscon caps with the DC setting. They should read 17.8V DC. Right, Jeremy?

Folsom · « **Reply #672 on:** 20 Oct 2016, 06:29 pm »

Yes, something would be awfully wrong if you got a VAC reading!

KR500 · « **Reply #673 on:** 20 Oct 2016, 06:33 pm »

Thanks for that ,
I switched to VDC setting and got readings of 17.7 on the Oscon legs and 24.7 on the pcb power input connections
I watched a video on DMM use this morning and thought the presenter said you use the voltage AC setting for checking consumer electronic circuits ?
Appears the problem is downstream somewhere, can I use a meter to check each leg of the chip ?
When I initially installed the 431 backwards I removed it and cleaned the eyelets with desoldering braid before installing a new one. Hopefully there wasn't something overheated from that procedure.

Folsom · « **Reply #674 on:** 20 Oct 2016, 08:31 pm »

Have you tried to play music with it?

If you have power at OSCONs then you either don't have an input signal, or the mute/stby isn't working.

KR500 · « **Reply #675 on:** 20 Oct 2016, 09:02 pm »

Yes. still no music
checked all pcb input/output and jack/post connections again . They look good
still get the resistance reading when touching probe to chip tab and probe to heat sink
Let me try putting a shoulder washer on each side of the chip

Folsom · « **Reply #676 on:** 20 Oct 2016, 09:09 pm »

No, stop. That has NOTHING in the whole damn world to do with getting sound or not. You could have the chip mounted with no mica, no thermal paste, and no washer and it would play music just fine. (You would hear the radio playing through speakers when music was not, however, and lose power due to excess heat)

Either the chip is bad, the mute/stby network isn't working, or you have no incoming signal. There is no other option. You have power to the chip. The signal is either not there, or is turned off, or can't turn on (bad chip).

Show a picture of the mute/stdby area that's to the left of the chip (one cap two resistors). Double check your capacitor placement for the input to make sure you didn't shift them too far to the right and skip the first hole or something.

KR500 · « **Reply #677 on:** 20 Oct 2016, 09:39 pm »

Folsom · « **Reply #678 on:** 20 Oct 2016, 10:47 pm »

And the input caps under?

KR500 · « **Reply #679 on:** 21 Oct 2016, 01:08 pm »