F-2624 Review

I would like for the community to take a look at my 2624 build to see if there any mistakes. After my recap I am having a tough time getting the unit to work. I am using a DBT with the 2624 out the unit will come out of protection. with it in the unit will stay in protection mode.

 

What does the underside look like?
What unit is this unit for?
Did you set the VRs for min bias and min offset for the testing?
What are the blue and gray wire voltages going to the protect board?

 

What does the underside look like? See picture
What unit is this unit for? 9090DB
Did you set the VRs for min bias and min offset for the testing?
What are the blue and gray wire voltages going to the protect board? Blue unstable, Gray ~ 60V

 

R34 looks burnt - suggesting excess current drawn by the circuitry containing TR02,04,06,08.

 

R34 checks good.

 

I'll delve into this later tonight. It takes time as I need to compare every semi-conductor to my good board pictures.
Out of curiosity... what's the device replacing the STV-3H temp/co diodes made of and what is it's anode/cathode?

 

The device is just the 3 diode solution is series. Didoes are covered in heat shrink then glued to a metal terminal then encased in epoxy.

 

Whoa! Is it safe to turn a 9090db on without F2624 in it? I just posted a new thread about what a mess F2624 is in a 9090db I just got that won't come out of protection. If I can trouble shoot any other potential protection issues with F2624 out that would be awesome. This is the first I've heard of doing that despite a long morning of AK 9090db back-catalog reading.

 

yes, in fact it's a pointer to other issues if there are any... Just be double sure that when you reinstall the 2624 that it isn't one pin off. That causes other problems.

 

@joe camilli your board appears intact in regards to component orientation. I've verified semi-conductors and resistors.
I hope the red lead on your STV-3H replacement device is the cathode (-) and the white is anode (+).
If you got 60VDC on the gray lead under the PS board it's full rails voltage and that means something is terribly wrong.

Check the power transistors on the back of the unit - verify one or more are not shot!
Stay on DBT (I hope you're powering up the unit using one).

BTW: That R34 sure looks like it suffered heat damage and John already pointed out to a possible reason.
It doesn't matter if it checks good, the circumstances aren't. You need to be very careful with the bias trimmers settings when you power on the unit.

Are the LED's doing anything on power up?

 

I suggest checking TR15, TR16, TR17 and TR18 to make sure the lead placement is correct. Hard to see, and not knowing the type of transistors you inslalled, but most modern transistors in a TO92 case are pinned as BCE, or ECB. You 4 transistors appear to installed with the C going to the base connection on the board, which would mean that the B or E connection is incorrect as well.

 

There appears to be a lot of solder on the top side of that board.

Is TR12 bridged on the bottom of the board?

When I had an issue with voltage on the gray/blue wires, it was a bad TR05 or 06. Then after replacement I had a hell of a time getting the unit right because of the effed up SM and that crap about the bias and offset adjustments and the channels they go with. Just knowing that section of the manual is messed up but good, it is what caused the TR to pop in the unit I did, helps.

You need to have the bias all with way down when powered on until it is adjusted. Find the correct diagrams here on AK for that. The offset should be set to a good setting also. If you have the old VRs and know which is which you can get the reading from them and set the new ones to something similar and see if you can get that 60V (you on a dim bulb, I got 47) to come down to operating level.

 

Good eye! Took me a while to figure this one out. I think Blue means TR-11 and as far as I can see, there's something fishy with the solder blob between collector and base.

 

Thanks for all the input I will update soon. Work is keeping me busy

 

No solder blob just a piece of fuzz

 

All power transistors test as good.

 

What about those open holes on the board for different lead spacing components? Shouldn't those be filled with solder? It looks like in some spots there isn't going to be a lot of copper connecting the traces.

 

R34 has been replaced. Another clue with the F-2624 installed none of the front panel lights come. Remove the board and they all come. Obviously in the process of recapping i messed something up - need some more tips on troubling shooting. Wife is wondering what happen to a simple project..........

 

The cool thing about F 2624 is the mirror image, I spent some time comparing resistance and diode measurements between both sides at various points, which helped me isolate some issues. Trace the diagram to find resistors that isolate a section of the circuit, lift the bridge leg then measure and compare. It prob goes without saying, but testing components in circuit vs out may not reveal issues.

The lights not coming could be related to a short. If the draw is too great maybe theres not enough voltage to supply the lights...

Did you rebuild the power supply board as well?

With board removed do you have tune and signal strength needle movement on AM of FM?

See what kind of voltage you're getting with the board removed vs installed and you'll know what kind of draw the DBT is picking up

 

The fault wasn't the resistor, it tested good before. It was what's causing the R34 to overheat and exhibit heat damages. The clue is with the 60VDC you're measuring on the gray lead at the bottom of the power supply (F-2656) board. That means full rails voltage on the channel with the gray lead, so it's possible either the driver power transistors are fully open on that side, or there's a short. Ignore it, and you'll keep burning R34.

This could be a mechanical stress issue with the power supply PCB. One or more of the traces may be hairline fractured and stop conducting when the driver amp is installed due to flexing of the power supply PCB. It's not unheard of, so you may want to clean the bottom of F2656 and start following the traces with a magnifying glass and a DMM to check continuity of the traces with the driver amp installed, so you can nail fractured traces. I'd start at the bottom where the driver amp connects and follow the traces. Also make sure the colored leads from the power transformer are connected to their pins on F-2656 according to the silk screen color coding. Another caveat is with the grounding of the F2656. It all converges to one of the corners (where the white and brown PU leads connect) and is held down by a screw to the chassis. You'd want to make sure that screw is tight and then to follow the ground traces with a continuity test.

Try to post some hi-res clear pics of the bottom and top of the power supply PCB. This is extremely difficult to guess through without visual verifications or in low-res images where a furball looks like a solder blob.