Wrong component in 8048 kit!

I have just purchased a Vellemann kit (PIC Programmer K8048) from Maplins in the UK. When I checked off the components, they were all correct except for Resistor R14. This should be a 3.3k resistor, but in the strip of resistors there was a 1k resistor where R14 should have been. All the documentation I had said that this should be a 3.3k resistor.

I have completed the kit apart from this item. Should I use the 1k resistor in place of the 3.3k resistor, or get another 3.3k resistor to replace it with?

I have also put this question on the other PIC forum - apologies if it is in the wrong place!

You can go ahead and fit the 1K resistor. Mine has the 1K and works fine without ever having had a problem.

The issue has been brought up before and has a response from Velleman, here:


It appears that the bandoliered component strip has been updated, but not the schematic in the documentation. The specified value in the build steps is correct though.



Now you’ve really confused me!

I understand you to say that the schematic may have an error - you describe a situation where the schematic and parts list are different. My situation is that the schematic and parts list AGREE, but the items provided are different!

The reference you give describes a situation where R14 and R16 are both either 1k or 3k. My parts list and schematic each give R14 as 3k3, and R16 as 1k. However, on the resistor strip, the resistor at position 14 was a 1k.

I am not sure I should go ahead and put a value in which is stated as incorrect in all my documentation, unless Velleman technical support OK it. But there seems to be no way to contact them?

Sorry for you being confused, but I am more than sure that one of the VEL’s will clarify that the 1K resistor is the correct value for the current board revision.



Sorry for misleading you - I’m even more confused than I thought I was!

On rechecking my parts list and scematic are different, but not for R14.

R14 is specified as 3k3 in the parts, 3k3 in the schematic, and I have 1k.
R16 is specified as 1k in the parts, 390 in the schematic, and I have 1k.

I did not notice the latter discrepancy, and put R16 in as 1k. Looking at the circuit, I see that R14 modifies the VPP, so a 1k would make it higher. Perhaps this was changed because of the reported difficulties from people using 12v PSUs? I actually have the opposite problem - I will be using an unregulated 18v supply, and I’m worried that it might be too high for the UA78L12…

Diagram values are indicational and subject to changes.
Partlist values should be followed.
1K for R14 is a mod which has not reached the partlist yet.
1K for R16 is OK

Thanks, VEL417.

I have now installed R16 as 1k. And, of course, it’s not working!

I am using an 18v PSU, (though only 200ma - might that be an issue?). I have checked the soldering as well as I can, and made up a serial line with only pins 3,4,5 and 7,8,9 conected, as advised.

When I apply power the power light goes on. When I switch to PROG mode, the warning LED flashes. When I set COM1, the software recognises a K8048.

When I try to write Demo.hex, the r/w led flashes momentarily, and then I get a warning - “No pic on board, Programmer must be set to PGM mode, PIC type must be matched to software, …”

The ‘controller’ is set to PIC16F627, the Config is set to 3F61, and there is a PIC16F627 in slot 18P. The two crystal jumpers are in.

What am I doing wrong?..

Short update -

I have changed to a 15v - 600ma supply to ensure that there is enough power. This PSU gives an unloaded voltage of 19.5v

I assume the PIC needs a 13v line to be written to. This line seems to be marked VPP on the schematic. I note that when I power up my board this line is +13.2v, but when I select PROG mode the line drops to 12.8, and when I start to write the line drops to 11 or below.

a) Does this explain the failure to write?
b) What might the problem with the board be, given I am using a PSU well in excess of specification? During a write attempt, the voltage at the PSU does not drop appreciably from 19.6v.


My panic has somewhat diminished. The dropping of VPP seemed to be associated with plugging the serial cable in, so I swapped the software to my old laptop and tried it there, thus using different serial port circuitry. It loaded the demo program first time and ran it perfectly.

So I suspect a lot of the problems reported with this board are due to modern PCs having serial port incompatibilities…?

Make sure your serial port is a ‘real’ serial port, and not some on-board usb-to-serial type…

Vel417, we seem to have passed in the night…!

Obviously there was some issue with my desktop serial port. But it was, as far as I knew, standard.

I am lucky to have access to many PCs here, so I could easily test another PC. But the first one I used, which failed, was not a new machine - it was about 4 years old. So if standard machines 4 years ago were not providing compatible serial ports for this kit, I would say the kit needs to be updated. Serial ports seem to be dying out…

It seems to be that the only [color=red]correct value of R14 is 1K[/color] and not 3K3. Only with R14=1K and R30=10K, ZD1=8V2 and the presence of D2 and D3 the correct Vpp of 13V is achieved. So, 3K3 is the wrong value (A Vpp of only 12.26 V is achieved, which is below the minimum required value. As far as I can see, most PIC’s require a VPP between 12.5 and 13.5V, so nominally 13V).


I’ve followed the thread so far and understand that, as per VEL417’s post the definitive values for R14 and R16 are :-

1K for R14 is a mod which has not reached the partlist yet.
1K for R16 is OK

On my component bandolier R15 is a 1K resistor (the parts list suggests 3K3)

Has this been changed too?



I have this same thing, R15 is detailed as being a 3.3K resistor but I only have a 1K resistor.

Please can someone confirm if it is okay to us the 1K resistor in R15.

Thanks in advance :slight_smile:


The value of R15 is not critical at all. Both 1K and 3K3 will do excellent, the resistor should be lower than 40K. :smiley:

Hello all!

It seems to be that the only correct value of R14 is 1K and not 3K3.
Only with R14=1K and R30=10K, ZD1=8V2 and the presence
of D2 and D3 the correct Vpp of 13V is achieved.

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