Diode identification

Thread Starter

BertyB

Joined Dec 18, 2020
9
Hi all. First time poster. I am currently rebuilding a Sega motor control board from G-Loc and I need to replace some diodes but I am not sure what types of diodes these might me. Below are some pictures and readings from my test gear. Any help greatly appreciated.

Diode 11
20201204_174014.jpg

20201204_174036.jpg

Diode 8

20201204_173457.jpg

20201204_173715.jpg
 

dl324

Joined Mar 30, 2015
12,871
Why are you replacing diodes that test good?

To identify possible substitutes, we need to know secondary voltages and currents involved.
 

Thread Starter

BertyB

Joined Dec 18, 2020
9
Hi. Thanks for the reply. In regard to why, the short answer is that there are multiple instances of these diodes used and these were the only ones that I could remove in one piece due to corrosion damage caused by rat urine.

Im not sure how to determine the secondary voltage as I have minimal detail on these boards and the other board is also too damaged to test. Any suggestions?
 

Thread Starter

BertyB

Joined Dec 18, 2020
9
Sorry, my English must be sub-par as I have not explained my dilemma well. I do not know the secondary voltage and current so I need to know alternative strategies to determine this.

Can you please give me some guidance on how I may be able to determine the secondary voltage. For example, can I extrapolate by looking at the value of capacitors in the circuit after the diode?
 

dl324

Joined Mar 30, 2015
12,871
Sorry, my English must be sub-par as I have not explained my dilemma well. I do not know the secondary voltage and current so I need to know alternative strategies to determine this.

Can you please give me some guidance on how I may be able to determine the secondary voltage. For example, can I extrapolate by looking at the value of capacitors in the circuit after the diode?
The definitive way would be to measure it. You could use capacitor voltage, but that should be a conservative voltage.

For current rating, you could look at what's connected to the secondary.
 
How did I get there? It basically feeds a 78M05 which has a max current output. This http://www.hammondmfg.com/pdf/5c007.pdf guide is also helpful. The topology is a half wave rectifier with a capacitor filter.

We also know that the regulator needs at least 5+3 or 8V input to function. 50V is a usual PIV (Peak Inverse Voltage) specification. the 1n400x and 1n54xx are standard diodes for use at power line frequencies.

In 12V automotive applications, 50V isn't a good PIV number because of the alternator spikes. 200 is much better to use.
Exceeding the PIV value can be non-destructive if the current is limited.

There are other types of diodes such as Zener and avalanche which are usually put in the same category. There PIV is precisely controlled. Shockley diodes are a metal semiconductor junction and have a low voltage drop. There are variactor diodes where the capacitance can be changed. Switching power supplies need fast recovery diodes. Most diodes these days are made of silicon. Germanium was an early diode material and even an early transistor material. Selenium rectifiers are a bird of a very different color.
 

Thread Starter

BertyB

Joined Dec 18, 2020
9
A question - given that many of these diodes are used in AC - DC conversion, would it make more sense to use some form of fast recovery diode?
 
A 1n5400, a 3A 50V diode should work fine in the applications.
No, that diode is wayyyy too slow as a SMPS rectifier like D8, D10 or D11. The diodes must be fast recovery.
One problem is Japan offers 1.5A and 2A rectifier diodes but North American semi's only offer 1A and 3A.
It would be UF5402 for a fast 3A part but these have fat leads 0.9mm and might not fit the PC board. BYV26A or SF4002 is closest to D11 (sintered glass package) 1A 200PIV fast recovery.

You can just scrub/wash the parts too, they don't look corroded.
 

Thread Starter

BertyB

Joined Dec 18, 2020
9
I've been comparing some ultra-fast diodes to the readings I got from the diodes I removed from the board. It seems like a FR207 gives the closest measurements to the ones I removed from the board at D11. The FR207 reads as Uf = 618mV C=10pF.
 

sagor

Joined Mar 10, 2019
439
No, that diode is wayyyy too slow as a SMPS rectifier like D8, D10 or D11. The diodes must be fast recovery.
One problem is Japan offers 1.5A and 2A rectifier diodes but North American semi's only offer 1A and 3A.
It would be UF5402 for a fast 3A part but these have fat leads 0.9mm and might not fit the PC board. BYV26A or SF4002 is closest to D11 (sintered glass package) 1A 200PIV fast recovery.

You can just scrub/wash the parts too, they don't look corroded.
This is a simple linear regulator circuit(s), not SMPS. Any 1N540x diode should work just fine, allowing up to 3A current to feed linear regulators that are limited to 1 or 1.5A themselves. In fact, some regulators in schematic at the "L" series, 100mA at most so a standard 1N400x series will do.
 

Thread Starter

BertyB

Joined Dec 18, 2020
9
Sega G-Loc has an SMPS, which means fast-recovery rectifier diodes are required.
Thanks for the response. I have a a selection of fast recovery diodes in my stocks anyway so it is no issue to put these on the board. I am thinking that for the smaller diodes e.g. D07 that a FR207 might be the closest match. I'll replace the 1n5400 at D8 with a UF5402.

Below is a picture of the circuit in question. Vacant spots on the board are for the smaller diodes.

20210201_143738.jpg
 
FR207 is still slow for D4.

D3 not sure what it's for
D4 is the primary snubber, needs to be HV and fast recovery, suggest UF4007 or BYV26E.
D8 +18V reg
D10 +15Va reg
D11 +15Vb reg

FR207 is 2A 1,000PIV 500nsec DO-15 0.9mm leads
BYV26A is 1A 200PIV 30nsec SOD-57 0.82mm leads
UF4007 is 1A 1,000PIV 75nsec DO-41 0.86mm leads
UF5402 is 3A 200PIV 75nsec DO-201 1.32mm leads

Do we know for sure none of the rectifier diodes are Schottky? They would run cooler for D8,D10, D11.
 
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