3D pedal design 


Hammond X5 Organ Repair and Installing the FlatKeys FK50240 Top Octave Synthesiser Chip PT2

Well here is part 2 of the Hammond X5 organ repair. After fixing all the issues that were addressed in the first post ill first post the list of problems identified so far that haven’t yet been fixed.

  • Half the key wouldn’t work
  • Percussion on the pedals made awful noises if and when present
  • There didn’t seem to be and difference in note on the keys that worked
  • Sometimes it would make a god awful bang.

Well the last problem on the list was the one I fixed first. As soon as I tried to check the voltages on the power supply it became blatantly obvious what was causing it. One of the wires, when touched, would reproduce the issue and seemed to move in the hold it was connected to inside the PCB.

Hammond psu

The wire in question is the orange wire, which provides the +15 volts to the preamplifier board and is marked +B1. After removing and touching up the solder joints the banging had gone, but when going back to check the voltages -B12, that is supposed to be -27, was fluctuating like mad on my meter. I’ve seen this before and if I would have got my oscilloscope out to check I would guess there would be some severe ripple on -27 volts. When you see your meter fluctuating, it is this ripple that is confusing the multimeter and can sometimes be measured with the ac setting. I didn’t do this because it was a pretty certain bet that capacitor C10 100uf at 35v next to transistor Q3 in the top middle of the picture above was bad.

Here is the schematic of the Hammond X5 Power supply.

x5 psu schem

As can be seen in the picture, this capacitor has the job of smoothing out the ripple on the -27 volt line. After this capacitor was replaced the meter read a steady -26.8 volts which is damn near -27. After a quick check of all the other voltages I was happy that I could move on and was hoping this had fixed a lot of the other problems and hadn’t created any.
Well sadly that hopeful optimism was short lived as it only seemed to fix the banging noise. The circuits that the -27 volts fed must not really care about ripple or may even have local smoothing and even regulation that means that the ripple was a not an issue. Either way it is better that it’s fixed. Now I started looking for the reason why only half the keys worked.
I first started pushing and pulling the connectors to see if the problem was just a bad connection but as soon as I pushed a connector on the amplifier and reverb drive board, sparks seemed to come from underneath. After pulling the board out this is what I found.

chip stuck to back of pcb

Now ignore the bodge wire job, these are common in old equipment. I was more interested in the chip hanging on to the PCB for dear life. It was a 74LS93 4 bit binary counter. I was starting to think this could be the issue with the notes not changing and the keys not working as an organ such as the Hammond works by generating a tone and dividing it up to make each individual note, as far as I understand (I do stand to be corrected). This was leading me to think that the binary counter could be used in part of this division so I started to look for where it may have come from. Sadly this idea fell flat when not a single chip socket was found to be unpopulated, but this does tell me that somebody may have been here to fix this exact same issue before me and more than likely, caused further damage.
The only 74LS93 I could find was on the MDD generator board. This board is also where the -27 volts from the power supply go.

MDD gen board hammond

The two chips at the top of the board are MM5832 and MM5833. They are responsible for dividing the clock down into its respective notes. Looking at this part of the schematic it started to reveal that maybe the issue was with the missing keys.

MDD part schem

As we can see the two chips to the right of the schematic (IC2 and IC3) are nicely labelled to show which note each output produces. As the note IC3 corresponded to the keys that wouldn’t play, I was pretty confident I was onto something. Before I cracked out the oscilloscope I decided that I would check IC1, the only 74LS93 I could find on the board that was the same as the chip found earlier in the repair. This is the response I got from my Wellon programmer that also doubles as a logic tester.

hammond x5 7493 test

To no surprise, the one I found under the board gave a similar result. I was hoping that the two top level octave divider chip had survived and this was the only casualty. The thing that I kept thinking about was the problem with the -27 volt supply. I think that the problem with the supply had taken the chip out and then was replaced hence why I found one floating around under the PCB.
I got my oscilloscope out and looked for an output from the MM5832 and MM5833 with signals looking good on the input. One was outputting a signal, but the other was stone cold dead. I looked at the schematic and decided that switching these two chips would alternate the keys that function (all be it out of tune). This test confirmed that the IC3 was dead.
This was a bit of a setback as these chips have been out of production now for quite some time. Luckily a bit of internet searching lead me to a website call FlatKeys owned by a guy called Chris Burrell who makes and sells logic replacements for these chips. He also deals with an assortment of other hard to replace chips for organs and sells them at a very reasonable price. The added bonus was with the FlatKeys FK50240 top octave synthesiser chip I could also add a transpose switch and an octave switch to give the X5 some new sounds that the original was incapable of (think of the start of Stargazer by Rainbow….well that was the only one I could do).
I asked Chris if he could send me an example of it fitted to an X5 and almost immediately got an email back showing just that.

flatkeys install exampleAs we can see here the replacement has two ribbon cables that go to the MDD board and plug straight into the sockets where the old chips lived.

This gave me confidence that this was the right move and rang the owner of the X5 to see how he would like to proceed. This was greeted with excitement and he quickly ordered the parts and within a few days brought them round to the workshop for me to install.

The kit came with a small circuit board with the ribbon cables already attached in a black project box all screwed together for safe transport. Along with this there was a multi-position rotary switch that was already wired up to an octave switch. This was attached to a plug for an easy install and a transpose switch again connected to a plug. As this kit is made for various organs and keyboards no mounting holes have been drill so firstly I set about drilling and cutting the project box.

flatkeys lid

Here you can see I’ve cut a slot for the ribbon cable and a cutaway for the switch plugs. It could have been a bit nicer but I didn’t have a file handy. I also at this point drilled some pilot holes to hold the box to the back of the organ.

flat keys box installed without lid

This is with the box and board installed and switches plugged in ready to test before fitting the lid. Before I moved on and got to testing there was a little modification that needs to be made to the MDD board before the FK50240 will work in and X5

flatkeys install MDD mod

This is the install modification that Chris sent me that has to be made before moving on. As you can see R12 has to be replaced with a wire link and R13 removed. I could have just put a jumper over R12 and snipped R13 out to make life easy but I decided that I would do it proper and make it look good.

MDD with resistors marked

The photos I took after the modification were all blurry so in the picture above I’ve added two coloured arrows. The green arrow points to the resistor R12. This one needs replacing with a wire link or jumper. The yellow arrow points to R13 and that needs removing from circuit.
After the MDD board has been modified all that is left to do is remove the MM5832 and MM5833 from their sockets and insert the respective plug from the FK50240 (these for me were handily labelled).


Flatkey install without controls

Here is a picture of my install as you can see I pretty much copied the example given to me by FlatKeys. After this I hooked up the controls and gave it a quick test. At this point all the keys jumped back to life and I moved onto finding places for the new controls. Me not being well up on playing organ I decided it was best to contact the organs owner and asked for some direction.
Ill wrap it up here and finish this off hopefully with a part 3.


Hammond X5 Organ Repair and Installing the FlatKeys FK50240 Top Octave Synthesiser Chip PT1

This Hammond X5 came to me with various issues that are common with these old organs and sometimes unless you have a lot of spare time on your hands are not economical to repair. This particular example would probably come under that bracket but me being me I decided that I’d give it a go.

hamond top open big

The organ would only make horrible noises when it was dropped off for the repair that was a new issues that wasn’t on the to do list before I  had even started. I sounded all distorted and sometimes would suddenly sound alright for a split second. This beings as it had only just been transported smacked of a bad connection but no amount of wiggling connectors especially the ones from the amp and volume pedal did nothing. So I started tapping on thing to see if I could aggravate the issue and as soon as I tapped on top of the amp that is house in the pedal board assembly in sound would jump back every time I tapped. So out came the pedal board.

hammond pedal board amp side

As you can see the pedals are on the left. The volume pedal is in the middle and the silver box to the right is the amplifier (The amplifier is a solid state in the X5.). After opening the amplifier cover I could immediately see that I wasn’t the first person here. Not surprising given the age of the instrument.

hammond x5 amp open

Here you can see the large transformer to the left, the bridge rectifier in the upper middle, large reservoir caps to the upper right and main power amp module with the PCB attached to a heat sink. As the problem was most likely a cold solder joint I started with a quick inspection. There were lots of joints that looked suspect which kind of got me a bit worried about the condition of the rest of the organ.

hammond amp pcb

My plan of attack here was a more of a shotgun approach as every joint looked suspect. I soldered all of the joints and was kind of confident that it would solve the issue and luckily it did. Due to the solder looking bad it will probably stop the organ from developing a problem further down the line. I tested the amp with a 1kHz sine wave and all looked good.

amp sine test

Ignore the tiny bits of distortion and voltage as I’m sure this was done unloaded and was really just to see if the amp was working.

Now with the amp plugged back into the organ the other host of problems became apparent. Here’s the list I wrote down at the time (please note I don’t play organ and some of my terminology make be incorrect).

  • The volume pedal was very twitchy. I put that down to a bad pot, but it wasn’t as you’ll see later.
  • Half the key wouldn’t work
  • Percussion on the pedals made awful noises if and when present
  • There didn’t seem to be and difference in note on the keys that worked
  • Sometimes it would make a god  awful bang.

Now with all that said these were just the ones I wrote down at the time and didn’t really cover anything such as cosmetics or noisy controls but gave me a plan of attack to get the organ somewhat useable first.

My next job was the pedal as it was still exposed and ready to work on, hence why it made the top of the list.

Hammond volume pedal top

Here we can see the pedal without its rubber cover as I was trying to save time getting to the potentiometer to clean it but was slowly beginning to  realise it didn’t have one.

hammond vol pedal back

What the X5 uses is a bulb and an LDR (light dependent resistor) to gauge the position of the pedal by using a slit that has a blocking plate that moves in front of the LDR to adjust the amount of light it sees from the bulb. I pulled out the bulb to make sure it was seated in its holder and this happened.

hammond pedal bulb

Now the bulb didn’t seem too secure, but if the loose wire was the issue then I’m not sure. After re-attaching the wire and a quick once over of all the joints with fresh solder it seemed fine and was working once again. I gave the entire board a quick clean up and made a nice new shroud for the pedal out of card. I think it may also have a part to play as the light was getting in and the bulb was not working. Here is a picture of the old shroud.

pedal board shroud

I didn’t get a pic of the new one, but I’m sure we can all use our imagination and accept that I did an awesome job and it didn’t look like a one year old did it honest.
Anyway I’ll leave this here and come back with a part two as this one is going to be long and me having to remember every detail is also an issue here.
See you later for part two where it all gets a bit mad and I add a bit of a twist provided by FlatKeys.



Peavey 600E repair

I got asked If I could save this amp by a friend that as a rehearsal/recording studio. Everyone of the front XLR’s were shot and Peavey want more than the amp is worth for the parts


This said its a reasonable amp for a rehearsal room so I decided that Id sort it. First thing to do was get the case off and look at how the inputs were connected to the PCB.



As can be seen these are custom pcb mount XLR’s used by Peavey and was going to take a bit of ingenuity to fix. The main issue I had was how much room do I have to play with. Its tight but I decided that chassis mount XLR sockets (the one seen on stage boxes were the way forward.


These were a bit of a square peg in a round hole but at £9 a piece for the proper Peavey replacements (that I might add are shite) I was gonna make them work. After some filling drilling and pop riveting we had this.


I know not bang on but what do you expect its functional and will be 100 time more robust than them special Peavey sockets and in a rehearsal room they get punished day in day out.

After Making the new sockets fit I had the slight issue of having to make the connections on the back of the sockets reach were the old XLR’s once went. This was taken care of by using some shielded wire I had left from a multi-core I had just made up for another friend.


The connections are wired from the back of the sockets to the other side of the pcb and connected to were the Legs of he old XLR sockets once stood. This is a 100% better solution as now the pcb isn’t taking all the strain every time a mic lead is plugged in and out.

After reassembly the amp looks a bit different but it was never a marvel to look at in the first place not like it is a Soldano is it.


Well its a easy fix but took a good bit of time and I’m sure it will go on to provide a good few more year service.

Coming up is a Hammond organ and a VOX AC50 Ive just been really busy but Ive not forgot about the blog

Peace out.

Crown K2 power amplifier repair


This Amplifier would sometimes work , sometimes would not and other times it would just shut off for no reason. These faults can be very hard to track down but these amps when the go wrong and its not the power transistors then it normally down to the caps on the main board. Capacitors tend to drift out of spec as they age and also increase in ESR. A lot of caps when they go bad have visual signs. These signs can be bulging tops or bodies from pressure that as built up inside from getting hot or electrolyte leaking from them onto the PCB they are attached to. Not all caps will show these signs but will still be bad and this is a classic case I had right here.

First things first if you intend to play about in side a crown K series amp you need to trip the crow bar to discharge the main capacitors or risk a very unpleasant shock. ( you have been warned)

To do this you need to short out TP1 on the main PCB to the nearest resistor leg. Looking at the picture its pretty hard to see the actual test point as it can be obstructed by the resistors.


While doing this be very careful not to touch the heat sinc as this will be at a different potential to the test point and the resistor legs until it as been discharged.

Now That I had the amp discharged and safe to touch I set about removing the PCB. This is a picture of the rear panel that has the input and main board attached to it.


The back panel unscrews and will slide out of the amplifier with the PCB’s attached after all the wires from the harness have been disconnected (Be careful with the screws the small ones go on the side of the main board).

Once the input board as been removed I could get to the main board and see all of the caps that I was interested in checking.

Most of the people I’ve ever spoke to regards Crown K series amps as always told me that if its acting up to check all the 100uf caps and replace any that are suspicious. Well there are a lot of caps on this board and I wasn’t in the mood for doing them all so normally I would grab a ESR meter but that’s broke. So another way to check ESR was with my scope and a function generator. its not as fool proof as with a meter but it gives a good indication of a bad capacitor from a good one. What you do is pass a 100khz square wave into the capacitor while observing the same signal on a oscilloscope. For this to work in circuit you need to make sure that your signal in lower than 500mv so as not to turn on any semiconductor junction’s. What happens when you see a good capacitor is that the resistance at 100kHz is almost a flat line with slight waves in it as a capacitor is almost a short circuit at 100kHz AC. A bad capacitor with higher ESR will have resistance at this frequency and will just reduce the amplitude of the waveform on the scope.

Picture of good capacitor

( you can see how the waveform as collapsed as the capacitor acts as a short)


Picture of bad capacitor

(The wave form is still present due to the bad capacitor having a resistance and not shorting the signal)


With this method I found four truly bad capacitors and two suspect capacitor on the main board. These were all 100uf that seems to back up the advise Id been given.

The two capacitors that I believe cause this issue are c23 and c24. These are the two capacitors on the right of this picture.


Along with the capacitors there are a few other things that I was advised to check just in case. These were some resistors on the main board that age badly and drift out of spec. Although these resistors were fine on this amplifier I’m going to list them for my reference and anyone else that may have issues with a K series.

Resistors r136 and r236 should both be 33r next to the big white transformer.


Resistor r5 that is a 1/8 watt at 47k

k2 r5

Well The amps been used for 3 gigs since the repair and no complaints yet. Ill probably come back and do some editing on this page but for now ill just stick it out there.

Cheers Kris

Studiomaster Diamond pro 8-3 Repair

This desk came to me completely dead no power lights or anything. These desks are pretty simple beasts and there really isn’t much in them to go wrong. With the symptoms I assumed that this was probably a case of a bad connection as they do seem to suffer from the multi-pin leads becoming corroded. On opening the desk I noticed straight away that the power supply output capacitors had bulges in the top.


This isn’t uncommon in electrical gear of this age as these components have a finite life. I checked the rails going to the channel strips for shorts but all measured well.

I removed the power supply PCB and found this.


Im not sure if this is factory bodge work or not but all the connections seem to follow the traces so maybe it was done for mechanical reasons.

After removing the capacitors and replacing with new ones with a slightly higher voltage rating had to do a bit of filing (always a good idea if you can make them fit)


The power supply was still dead. Not surprising really but now I went after the voltage regulators seen above the capacitors these are two lm317 variable voltage regulators and a lm7915 negative voltage regulator. These are used to produce the +15 -15 and 48 volt phantom power.


One of the lm317 reg’s was still happily working away but due to it being of similar age I removed and replaced all three for good measure. At this point all voltages were restored and I got the top of the console plugged in for a test.


The mixer was back from the dead. Left it playing songs for a few hours and kept a eye on its temperature around it heat sinc but all is now well.