- This topic has 55 replies, 6 voices, and was last updated 4 years, 8 months ago by
.
-
Posts
-
Paul – the errant +VB voltage supply is definitely going to create problems. Try this . . .
Remove all the chips and with the PCB unpowered, check for continuity between the junction of R32 & R33 to ALL the VB points – pin 5 of IC1 and the outside of R1. If you cannot confirm continuity between those points, there may be a micro-fracture in one of the traces. The fix is determine what manual jumper is required to facilitate a fix.
Also, have you verified that the authenticity of the BBD chip and that the jumpers match up? From where was the BBD chip acquired?
Cybercow,
That is my next order of business; remove the board entirely and test without any of the ICs. There must be a fracture in one of the traces but there could also be a bad component; R31 was reducing the voltage down 3 volts for instance.
As for the BBD, I am using a MN3007 I purchased from Amazon; yes, it was brought to my attention it could be defective/ recycled. I am not 100% certain but a defective IC3 shouldn’t be the cause for the errant +VB voltages.
Cybercow- apologies if my previous post was terse. I am going to come back to this board in a couple days to see if it can be fixed. I also have another on order with a V3207 chip from Barry’s shop.
You will fix it
Did you reflow R32, 33 and C13, 14 and 15 and carry out the continuity checks Cybercow suggested
It’s frustrating but you learn a lot debugging I find
Let us know you’re findings
You could remove the MN3007 only and see if that affects voltages it does share a common ground if it is a fake it may well be causing chaos
You can also do your resistance checks around the power section again as you know without power check from a reference point and see if you get expected resistance along that path e.g. R31 from 9v to the side connecting to C13 should be around 47ohms if it’s an easy path to check ie no paralell resistance to consider worth doing the checks
This will highlight shorts, bridges, open circuits etc with R31 for example if you get a much higher resistance you know it’s the correct value so maybe a dry joint causing high resistance to current flow or a dodgy resistor or a bridge etc
Unfortunately fixing it won’t come to pass. I planned to do some of the tests this evening and separated the pcb out of the enclosure with the two others. As I turned to get up, I accidently dropped it. At that point I backed up to take a look and in doing so, stepped on it. I was able to remove the B10K pot for later use, the C1M was snapped off its lugs. The board had several broken traces.
I have a couple more on order slated to be delivered soon. Billy and Cybercow, thank you for your guidance; it is much appreciated. I apologize my clumsiness let it go to waste.
Paul – I can’t count how many times I fried components, shocked myself, burnt traces, and yes – accidentally stepped on a customer’s PCB when I was starting out learning electronics. And while that was decades ago, it really does come together when we soldier on and figure out how to proceed. It’s a process. Electronics is a fickle mistress.
“Electronics is a fickle mistress.” You can say that again. Good news, my order of new PCBs came in and I was able to populate another Mini-Me. This time with a V3207 from the shop. The bad news is I have the same issue with a strong dry signal and no modulation. I started measuring the voltages across the board.
R31 drops the voltage to about 7.32V from 8.7. The voltage carries over all the way to R33 where it drops to nothing. Could anybody tell me which pads of R32 and R33 i can place a jumper to carry VB voltages over from the power supply to R1?
Note: I do get a continuity reading of 0.498 between the top pads of R32 and R33.
Paul – are both “G” and “G2” connected to ground? (G2 is a separate ground in the upper-left-hand corner of the PCB.) The G2 to ground connection is vital. (It is NOT connected on the PCB to better isolate the clock signal from the audio signal.)
And please pardon my confusion, but “continuity” is NOT a voltage measurement – rather, it is connected (continuous zero ohms measurement) or not. There should be “continuity” between the bottom pads of R32 & R33. Do you mean you are reading 0.498v across the top pads of R32 & R33? You should be reading ~4.5v across R33. Likewise, there should be a 4.5v voltage measurement across R32. R32 & R33 comprise a voltage divider and should be providing the +VB supply to the right side of R1 and pin #5 of IC1. (NOTE: Do NOT use G2 as a ground reference in any voltage measurements. Best practice is to use one of the two “GND” pads at the bottom of the PCB just to the right of the two “9V” pads.)
And with the V3207 chip, did you set the BBD jumpers vertically or horizontally? For the V3207 – those jumper MUST be set horizontally.
And if you’re getting a voltage reading of only 0.498 between the top pads of R32 & R33, then something is again “off”. With the circuit powered, the voltage between the top pads of R32 & R33 should be the same as the left side of R31 – a hair under the supply voltage.
The bottom pads of R32 & R33 are connected together and supply the “VB” voltage (1/2 of the supply) to the right side of R1 and pin #5 of IC1. The top pad of R33 should be GND and the top pad of R32 should be the full supply voltage as measured after R31.
“Oh what a tangled web I weave, when first I solder a pcb”
Hang in there Paul!
Cybercow- Let me address your response in bullets. Pardon my confusion as well.
- G2 is connected to ground, yes.
- I am using the second ground pad on the PCB for my black probe when measuring voltages.
- The jumpers are wired horizontally per the requirement of the V3207. 1n914 diodes for D1 and D2, a 1N4148 for D4.
- I retraced the voltage in the power supply by following the schematic. It stops at R32. i do not get readings at R33 or C15.
- I used my DMM in to measure continuity (Diode symbol mode) between the bottom pads of R32 and R32, It measures 0.0L.
- I may have been pressing against a incorrect pad to in my prior post to produce the 0.475 reading.
- The voltage at the top pad of R32 is 7.38V which is the same as the voltage on the left side of R31.
- The voltage at the top pad of R33 is 0 which it should be as ground.
- The voltage divider and VB voltages are where I get confused. I get 0 volt readings at R1 and pin 5 of IC1.
Paul can you remove IC3 from the board you are currently working on and give me the last 3 numbers from the batch code please?
Should be 588, 601 or 621.
Thanks.
Barry,
- The last three digits of the board serial number are 588.
- Point of clarification on continuity between the bottom of R32 and R33: i get a reading of 0.00 which shows continuity.
- With all IC Chips out and unit turned on, there is no continuity from either the bottom pads of R32 or R33 to R1.
- With all IC chips out and unit turned on, there is no continuity from either the bottom pads of R32 or R33 to pin 5 of IC1.
- With all IC chips out, I only get 7.47V to pin 8 of IC1. 0.0V to all other pins.
- With all IC chips out, I get 5.54V to pin 4 and 6.15v to pin 5 of IC 2. 0.0V to all other pins.
- With all IC chips out, I get 6.15V to pins 4-6 and 8 of IC3. 0.0V to all other pins.
- With all IC chips out I get 7.47V to pin 8. 0.0 V to all other pins.
- With only IC 1 in, I get
- 3.97V to pin 1
- 0.04V to pin 5
- 0.09V to pin 6
- 3.96V to pin 7
- 7.34V to pin 8.
Cybercow, see pics below.
- G2 is connected to ground, yes.
- You must be logged in to reply to this topic.