Electronics, programming, automotive etc.

I'm posting this here hoping to save someone else some time. I found most of this from the link below, by a strike of luck - the article is in German and does not show up in google search results.

The 944 throttle body tends to develop a vacuum leak at the butterfly valve axis seals. Replacing the old seals with o-rings is possible, but not the right solution. The original seals are radial lip seals and replacing such seal with an o-ring may work for a while, but this is not the correct solution.

The correct way is to replace the entire bearings, which include the seals.

The original bearing (INA F-95775) is no longer available - or perhaps it was never sold commercially. The current equivalent is the HK 0810 RS. The HK 0810 RS has a single side seal, like the original part. The HK 0810 2RS has dual seals and can be seen as an upgrade over the original parts.

These bearings are readily available from a number of different manufacturers.

The large o-rings should be replaced while the throttle body is off the car. I tried looking up cheaper replacements, however the original Porsche parts are actually reasonably priced - no reason to go aftermarket for these.
Part numbers:
Round seal 82 X 2,5 - 999 707 036 40
Round seal 65 X 3 - 999 701 331 40

There is also an o-ring at the TPS, that you may want to replace while you're in there. I will update this post when I have found the correct replacement.

Disassembly is mostly straight-forward. The hard part is removing the bearings. An M6 expanding brass anchor can be used to remove the old bearings (see link below).
These look suitable (M6 version): https://www.aliexpress.com/item/1005003512118808.html?spm=a2g0o.cart.0.0.35ff38datIqRmb&mp=1

When reassembling, the throttle plate screws must be secured. This can be done either by using split end screws or by using a high temperature thread locker.

The 944 NA and Turbo throttle bodies differ slightly (I believe one of the bearings is already a dual seal one) but as far as I know, they use the same bearings.

Removing the throttle body will let air into the coolant system, so the coolant system should be bled after the first test run, in case air bubbles have collected in the cylinder head. I also recommend a pressure test, to verify that there is no external or internal coolant leaks after mounting the rebuilt throttle body.

Source: https://www.stinni.de/index.php/porsche/drosselklappe

I've had some issues with my Porsche 944 sunroof. Clarks Garage has good instructions for the mechanical issues, but at the electrical side it falls short. I'm posting my findings so far:

Please go through the guide in Clarks Garage FIRST. I'm not covering any of the areas that he already covered.

The relay:
The relay pin numbers do not correspond to the pin numbers in the socket.
relay socket pin -> relay pin
1 -> 2 (sunroof SW pin1)
2 -> R (IGN lock via F36)
3 -> 30 (Positive via F8)
4 -> A (cruise control pin1)
5 -> 1 (passenger door pin1)
6 -> 15 (from instrument panel IIRC...)
7 -> 31 (GND)
8 -> 3 (Sunroof SW pin2)
9 -> 4 (sunroof SW pin5)

Checking for voltages in the relay socket:
Pin7 is GROUND
Pin3 is always +12V
Turn the key one click and get +12V to pin2
Turn the key one more click and get +12V to pin6
I believe pin5 gets 12V when the car is locked (haven't checked)
I believe pin4 gets 12V when the car is moving (haven't checked)

If these voltages do not show up you have a problem with wiring, a blown fuse or a problem with your ignition switch.

bench-testing the relay:
In this case I'll refer to the numbers printed on the relay itself.

ground to pin31 , 12V to pin30. Check all remaining pins for voltage, you should have none.
Add +12V to pin R, you're supposed to get voltage at pin8 - I got +10V, and I don't know if you should be getting 10 or 12.
Add +12V to pin 6 (15 at the relay) +10V disappears from pin3 and +12V appears at pin2

I believe adding 12V to pin 1 or A should give +12V at pin9, but I'm not sure of wether it should affect (remove) any voltage to pin 8 or 2. I believe what this does is tell the motor to lock the sun roof in place if the car is moving or is locked. I'll update this when/if I figure out mine.

About the different models:
The Peavey 5150 should need no introduction.

The 5150II is a 5150 with an improved clean channel, and a modified distortion channel. It also has a different power supply and a few changes in the power section. You can't make a 5150 sound like a 5150II or vice versa without severe modification, but you can get them a bit closer by some simple mods.

Later, the 5150 was relaunched as the 6505, and the 5150II as the 6505+. They made no changes to the circuit at this point. If a 5150 sounds different from a 6505 it's due to different tubes, or the age of the components, not a change in design.

The 5150 2x12 combo is different from both the 5150 and the 5150II. Tone-wise it's said to be somewhere between the two, but I don't know this circuit.

The 6505+ 112 combo has a preamp nearly identical to the 5150II, but a new fx loop and power amp.

Make your 5150II sound more like the original 5105

This mod will make changes to the preamp section to make the ultra channel of your 5150II match the specs of the original 5150. This without affecting the clean/crunch channels. Your amp will be be growlier, more organic, more gainy and get a chunkier attack, but it will also become less tight. It will not sound 100% like the 5150, as there are some differences in the fx loop / power amp stage as well, but it will take it in the right direction.

This mod is also applicable to the 6505+ 112 combo, but the component names differ. 5150II head: Replace C17 (470pF) with a 470K and 0.0022uF capacitor in parallel Replace C2 (0.001uF) with a 0.022uF capacitor 6505+ 112 combo: Replace C5 (470pF) with a 470K and 0.0022uF capacitor in parallel Replace C26 (0.001uF) with a 0.022uF capacitor Replace R12 (37.4k) with 39k (R12 probably won't make much difference, the value is already quite close)

Bias Mods:

The 5150 is biased very cold. Cold bias gives higher output power and adds crossover distortion.Crossover distortion sounds scratchy/buzzy. There's too much, it will sound as if something is broken. Also, crossover distortion is most noticeable at low volumes. Hence, if you play loud your bias current can be set low to extend tube life. Some like the crossover distortion in the 5150, but a lot of people think it sounds better with a cleaner power section. Higher bias current will also reduce the max output power, thereby making it possible to attain power tube saturation/distortion/compression at a slightly lower volume level, which may be something you want.This mod will make the bias voltage adjustable:

5150: R68: Replace this with a 5k to 7k resistor and a 10k pot in series. Start out by setting the combined resistance to 15k (stock value) 5150 II: This amp already has the potmeter built in, but the resistor value is too large. Even with the bias set to max current,  the  bias is quite low. Replace R68 with a 5k to 7k resistor

EQ Mods:

The EQ on the 5150 isn't great. The main problem is that the mid control doesn't work in the right frequency range. In my opinion, its' focus point should be at a lower frequency. The tone stack on a guitar amplifier is usually a very simplistic design. Leaving every knob in the middle position rarely yields a "neutral" frequency response, and changing the value of one component will usually alter the response of more than one frequency band. Here are 2 ways to improve the 5150 Eq; It's probably best to do only one of these 2 mods:

OPTION1: Shift the mid frequency downward This is a very simple mod which will move the focus point of the MID band to a lower frequency. 5150/5150II: Replace the 50k mid pot with a 25k or 22.5k pot.Or, if you're lazy, solder a 47k In parallel with R95. This does pretty much the same thing. 6505+ 112: Exactly the same, except R95 is called R48 OPTION2: Make the mid frequency sweepable This mod will make your EQ sweepable, however, moving the mid freq position will also affect the response of the bass and possibly the treble bands. 5150: Replace R28 with a 10k resistor and a 250k pot in series. 6505+ 112: R28 is called R47

Like most consumer electronics, computers tend to break down due to low quality capacitors that fail before their time.  In this example, my brother's computer switched itself off after a period of instability, and would not turn on again.

Visual inspection revealed a bulging capacitor close to the south bridge. (Look at the pictures below, the top plate with the vents is bulging slightly) I de-soldered the part:


As you can tell from the pictures, the part is:
Manufactured by TK, max voltage 6.3V, capacitance 820uF, max operating temperature is 105 degrees Celsius, and it's from the ATWY series. 646A is a date code.

In most electronics repair situations you'd simply replace the broken capacitor with a new one of equal capacitance and the same or higher voltage rating. This part measured an ESR of less than 1.1 ohms, which for most circuits would indicate a healthy component. In modern computers however, specs are much tighter, and parts that would work perfectly in most circuits can make a computer fail.

A google search for "TK ATWY" led me to the data sheet, which revealed that this 6.3V, 820uF capacitor has an Impedance (other word for ESR) of 0.036ohms, and a max ripple current of 1140mA.

We're looking for a part with the following specs:
Capacitance: 820uF (this value must be identical to original part)
Voltage: 6.3V (this value can be equal or higher)
Temperature: 105C (look at the placement of the part; how hot will it get in that position? In this case, very close to the South Bridge; 105C or more is recommended)
Impedance/ESR: 0.036 ohms (this value must be equal or lower, but not too much lower)
Max Ripple current:  1140mA (this value can be equal or higher)
Physical dimmensions: Diameter: 8mm (just make sure the part you order will fit on the board)

Then simply make sure you get the polarity right, and the board should work again. If not, this means the failing capacitor probably blew other components as it went out of spec. In most cases, replacing the faulty capacitor(s) solves the problem.

After a repair like this it's probably a good idea to clear CMOS+RTC, just in case something got corrupted when the computer became unstable.

I decided to buy a selection of 12AX7 tubes to find out how they differ. Remember to switch to 480p for better sound quality:
I tested the following tubes:
JJ ECC83 S
Shuguang 12AX7-B
old used chinese 12AX7A
Sovtek B
Sovtek LPS
Mullard Reissue
Svetlana Reissue
Tung-Sol Reissue

I tested the tubes by placing it in the V1 position, which is where 75% of the tone is made. the other 3 tubes (the last 25%) are Shugang 12AX7-B.

Settings on the rock master is ultra channel, gain pulled, max gain, EQ 3, -3, 3. The cabinet is close miced using an E906.

To get the same performance on all tracks I prerecorded a clip of dry guitar, and fed that to the rock master using a reamp box.

In my opinion, the differences between the tubes are negliable. It was however possible to reveal some difference by comparing two out of phase samples.